ABSTRACTS SUBMITTED TO THE
NORTH AMERICAN SECTION MEETING
OF THE IUSSI – OCTOBER 2004
Dear IUSSIers
We have an excellent turnout for our October meeting at Camp Tontozona, Arizona, with about 70 abstracts submitted thusfar. We will continue to accept abstracts for poster presentations until about mid-September; these abstracts will be periodically added to this page.
Abstracts are arranged alphabetically by first author, with the listed addresses being those at the time of abstract submission.
Abouheif, Ehab
Department of Biology, McGill University, 1205 Avenue Dr. Penfield, Montreal, Quebec, Canada HBA 1B1
Wing polyphenism in ants evolved once, 125 million years ago, and has been a key to their amazing evolutionary success. I characterized the expression of several genes within the network underlying the wing primordia of reproductive (winged) and sterile (wingless) ant castes. I show that the expression of several genes within the network is conserved in the winged castes of four ant species, whereas points of interruption within the network in the wingless castes are evolutionarily labile. The simultaneous evolutionary lability and conservation of the network underlying wing development in ants may have played an important role in the morphological diversification of this group and may be a general feature of polyphenic development and evolution in plants and animals.
Adams, Rachelle M.M.
& Christopher Roesel
Section of Integrative Biology, 1 University Station C0930,
University of Texas, Austin, TX 78712
Social parasitism, a widespread phenomenon, ranges from birds to insects. Social parasites exhibit numerous behaviors, including the stealing of a host's food and kidnapping and enslaving host offspring. Using phylogenetic, behavioral, and chemical-ecological information (alkaloids), I investigate the origins and evolution of parasitic behaviors in Megalomyrmex ants.
The genus Megalomyrmex is an ideal system to reconstruct the evolutionary transitions to social parasitism, because of variation in the degree of parasite-host dependence. Of the 31 recognized Megalomyrmex species, eight (silvestrii species group) are associated with fungus-growing ants. Their behaviours range from obligate to facultative parasitism to strict fungal and brood predation (Adams 2000; Brandão 1990; 2003).
Although the genus Megalomyrmex is taxonomically revised (Brandão 1990; 2003), phylogenetic relationships among these well-defined species are unknown.
Here, I use DNA sequence data to construct a phylogeny of the genus Megalomyrmex. I then examine the evolution of behavioral and alkaloid traits to further understand the origin of social parasitism in the genus Megalomyrmex. I specifically identify ancestral characters shared by the social parasites and the free-living species. Future expansion of the phylogeny, coupled with behavioral experiments and natural history observations, will allow me to elucidate conditions facilitating the evolution of social parasitism.
Adams, R. M. M., U. G. Mueller, T. R. Schultz, and B. Norden. 2000. Agro-predation: Usurpation of attine fungus gardens by Megalomyrmex ants. Naturwissenschaften 87:549-554.
Brandão, C. R. F. 1990. Systematic revision of the neotropical ant genus Megalomyrmex Forel (Hymenoptera: Formicidae: Myrmicinae), with the description of thirteen new species. Arquivos de Zoologia 31:411-481.
Brandão, C. R. F. 2003. Further revisionary studies on the ant genus Megalomyrmex
Forel (Hymenoptera: Formicidae: Myrmicinae: Solenopsidini). Papâei
The
regulatory anatomy of social castes
Amdam, Gro V.,1 James H. Hunt2 & Robert E. Page3
1Department of Entomology, 1 Shields Ave., University of California, Davis CA 95616
2Department of Biology, University of Missouri, St. Louis MO 63121-4499
3School of Life Sciences, Arizona State University, Tempe AZ 85287-4501
A conceptual framework has identified a set of regulatory structures that may be responsible for the evolution and maintenance of behavioral and physiological castes in social Hymenoptera. The explanatory power of the framework is demonstrated by individual-based simulations and new experimental evidence.
Anderson, Kirk,1 Robert A. Johnson,1 Juergen Gadau2 & Jennifer H. Fewell1
1School of Life Sciences, Arizona State University, Tempe, AZ 85287
2Universität Wuerzburg- Biozentrum, Institut für Verhaltensphysiologie und Soziobiologie, Am Hubland, Wuerzburg, Germany 97074
A fundamental tenet of sociobiological theory is that differences in reproductive ability within eusocial colonies should be environmentally, not genetically based. However, populations of seed harvesting ants in the Southwestern US (Pogonomyrmex rugosus and P. barbatus) have a genetic caste determination system, in which workers are heterozygous at multiple loci, while their reproductively capable sisters (alates) are homozygous. Our data show that this phenomenon is widespread across the ranges of overlap for the two species, supporting the hypothesis that it is linked in some way to hybridization events between the species. However, its persistence in areas outside hybrid zones suggests this is not a complete explanation for its evolution. Linkage mapping indicates that a large portion of the genome is involved in caste determination, rather than a single “caste gene”. Finally, caste determination is driven in part by colony behavior. Queens of colonies showing caste determination lay homozygous eggs that do not develop into workers, suggesting that homozygous females may be culled during brood care.
Beshers, Samuel N.
Department of Entomology, University of Illinois, 505 South Goodwin Ave, Urbana, IL 61801
Caste theory predicts that social insect workers specialize
on restricted sets of tasks and so are able to increase their efficiency. In the leaf-cutting ant Atta colombica, undertakers are
numerous and are not specialists. In
trials with laboratory colonies, undertakers are captured and marked as they
remove corpses from the nest. About 30%
of the workers in a colony perform undertaking.
Undertakers perform numerous other tasks, including foraging, nest cleaning and
repair, processing leaves to go in the fungus garden, and care of the fungus.
They rarely if ever tend brood.
Undertakers are typically middle-aged to old workers, though younger
workers may sometimes remove corpses.
Workers of any size may remove corpses but most undertakers have head
widths in the range from 1.0 to 2.0 mm. The number of potential undertakers is
far greater than is needed to handle the typical load of corpses.
These results provide evidence of
design for efficient responses and allocation of workers at the level of the
colony, and imply that individual specialization and efficiency are less
important for the task of undertaking.
I will present a set of general principles for allocation of workers to
tasks in support of this argument.
Role of extra-floral nectar
composition on community structure of visiting ants to Passiflora
vines
Biani, Natalia & Lawrence Gilbert
Section of Integrative Biology, 1 University Station,
University of Texas, Austin, TX, 78712
Passiflora species posses extra-floral nectar glands that maintains a defense force of predacious ants, vespid wasps and trichogrammatid egg parasitoids. There is a great heterogeneity in the amino-acid composition and concentration of extra-floral nectar across Passiflora species. The diversity of ants visiting the extra-floral nectar of Passiflora species was studied using artificial nectar solutions. A total of 24 ant genera visited the nectaries. Occasional visitors include small bees, orchid bees and other Vespidae. The most common ant genera were Crematogaster, Pseudomyrmex, Oligomyrmex, Pheidole, Solenopsis, Wasmania, Azteca, and Camponotus. There is an apparent lack of correlation between the composition and concentration of aminoacids of the extra-floral nectars and the species of insects attracted. This result can be interpreted under the concept of diffusiveness in coevolutionary responses, i.e., Passiflora species and their defensive insects do not show a specific and vital relationship, as in other more obligated mutualistic interactions (such as Pseudomyrmex and Acacia). Considering the abundance of arboreal genera, such as Crematogaster, Azteca, Zaryptocerus, it can be inferred that the species visiting nectaries belong to the arboreal communities.
Symbiont conflict in Acromyrmex
leaf-cutting ants
Boomsma, Jacobus J.
Institute of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen East, Denmark
Symbionts are great to have for the mutualistic services that they provide, but are often not the unambiguously benevolent partners that they seem to be. Vertical transmission generally helps to align the reproductive interests of hosts and symbionts, but also creates options for symbionts to pursue their own interests at the expense of the host. Wolbachia bacteria are a well known example of endosymbionts that manipulate host reproduction to their own advantage, but examples of ectosymbiont manipulation are less obvious: they have less power to affect host reproduction and their potential conflicts with the host concern elusive traits such as dispersal and symbiont mixing.
The fungus growing ants are hosts of vertically transmitted ectosymbiont fungi and are thus ideal model systems to test current evolutionary theory about mutualistic cooperation and host-symbiont conflict. I will present experimental work with two Panamanian Acromyrmex species to show that single strain clonality of fungus gardens is actively maintained by the resident fungus strain, even though it might well be in the long-term interest of the ant hosts to rear multiple strains.
The effects of calcium on food
preference of the termite Reticulitermes
flavipis
Botch, Paul
Department of Biology, Southeast Missouri State University, Cape Girardeau, MO 63701
Calcium is an important micronutrient for growth and development in most insects. We looked to see if the termite Reticulitermes flavipis preferentially chose food containing calcium to food without calcium. We presented colonies with a choice between an artificial food source laced with calcium and food without calcium. Colonies were tested in both the spring and summer. The results demonstrate that termites prefer the calcium laced food in the spring but showed no preference in the summer.
Endocrine changes in maturing termite queens
Brent, Colin & Ed Vargo
Department of Entomology, Campus Box 7613, North Carolina State University, Raleigh, NC 27695-7613
The winged alates of termites are prevented from reproducing while nesting in their natal colony. It is not until they leave to establish their own colony that they are able to develop functional ovaries and begin to produce eggs. Evidence indicates that their reproductive development is sensitive to cues provided by nestmates, a sensitivity that has evolved to regulate colony reproductive dynamics and caste composition. The physiological response is controlled by an underlying endocrine mechanism, which we have examined using the dampwood termite, Zootermopsis angusticollis. We made a detailed study of the circulating levels of hemolymph JH and ecdysteroids, and the ovarian development of maturing primary reproductives as they experienced different social stimuli. Similar data was collected for fully mature queens and immature “workers”. During a 45-day observation period, we found significant changes in JH and ecdysteroid levels and these appeared to be coordinated with the observed ovarian changes. We also found that social stimuli known to effect reproductive development and oogenesis in these termites had commensurate effects on the endocrinology. The data are sufficient to develop a basic model of the endocrine mediation of the social regulation of reproduction in termites.
Thermoregulatory trade-offs resulting
from vegetation removal by the western harvester ant (Pogonomyrmex occidentalis)
Bucy, Ave M.
Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309-0334
I explored the hypothesis that a seed-harvesting ant increases its time for activities outside the mound by exploiting a thermoregulatory trade-off in nesting behavior. Western harvester ants, (Pogonomyrmex occidentalis), are conspicuous residents of shortgrass prairie in western North America. Worker P. occidentalis actively clear all vegetation from the immediate vicinity of their large gravel mounds. The reasons for maintenance of this bare perimeter are unresolved, but vegetation removal clearly eliminates shading of the mound by plants. To test the hypothesis that a seasonal trade-off in ant activity results from this vegetation removal, I measured the effects of shade on activity patterns. Experimental shading of ant mounds shifted daily activity patterns by lowering ground temperature. By removing vegetative shade, ants gained activity time early in the day, at the expense of midday foraging time. A model derived from field data predicts surface ground temperature (and therefore ant activity) based on air temperature and solar radiation, under sunny and shaded conditions. For each of six years modeled, shade removal yielded a net gain of activity time. These results show a thermoregulatory effect of vegetation removal by harvester ants, helping to maximize activity time.
Reproductive
conflict in Bombus
impatiens colonies
Burns, Ian & Marla Spivak
Department of Entomology, University of Minnesota, 219
Hodson Hall, 1980 Folwell Ave., St. Paul, MN
55108
Significant differences in non-cooperative behaviors of confined and free flying Bombus impatiens colonies were observed, particularly in the timing of worker aggression towards queens, but also in the nature of the behaviors themselves. Priming of egg cells with pollen, a behavior widely reported for Pyrobombus species, was seen to be closely associated with aggressive worker/queen conflict, and such pollen priming was not possible for non-foraging colonies. No correlations were found between the timing of competitive behavior and the production of reproductives: no split sex ratios were found; virtually no worker oviposition was observed; vigorous opposition to queen laying was common.
Reduced kin recognition in the success of a widespread African ant, Lepisiota
incisa
Caldera, Eric J.
Section of Integrative Biology, 1 University Station C0930, University of Texas, Austin TX 78712-0253
Intraspecific competition for resources is often the factor limiting worker population size in ants. Energy expended on competition would otherwise go toward colony growth and reproduction. A loss of intraspecific aggression upon introduction has been key to the success of many invasive ants including the Argentine ant. The African Black Sugar Ant (Lepisiota incisa) may be capable of displacing the Argentine ant. While L. incisa is native to Africa, it is considered a pest in many parts of South Africa and population numbers of this species have rapidly increased in Kruger National Park, South Africa, in the 1990’s. This study tests whether L. incisa has also experienced a similar reduction in intraspecific aggression. Intraspecific aggression assays were conducted within and among four sites in Kruger National Park. My results show that that L. incisa does have reduced intraspecific aggression. This reduction in intraspcific aggression may help L. incisa escape energetic costs associated with intraspecific competition, thus making it a potential threat to ground-dwelling biodiversity in Kruger National Park and South Africa.
Cooperative breeding in thefire
ant: a test of reproductive skew
Cassill, Deby,1 Indira Kuriachan2 & S Bradleigh Vinson2
1Department of Environmental Science and Policy, University of South Florida, Davis Hall 221, 140 7th Ave. S., St. Petersburg, FL 33701
2Department of Entomology, The Texas A & M University, College Station, TX 77843
Cooperative
breeding among unrelated ant queens presents a conundrum. Why should
subordinate queens join a group only to have their reproductive capacity
reduced by a dominant queen? In this paper, the egg-production and survival of
cooperative queens (polygyny) of the fire ant, Solenopsis invicta were
quantified under experiment conditions. The major results were as follows: (1)
When cooperative queens were isolated from each other with equal resources,
subordinate cooperative queens laid fewer eggs and died at higher rates than
dominant cooperative queens. (2) When incubated in the same nest, the closer
subordinate queens were to the dominant queen, the more eggs subordinate queens
laid and the longer they survived. In contract, the dominant queen’s survival
and egg production was unaffected, negatively or positively, by differences in
the proximity of subordinate queens. (3) When given the opportunity to remain
isolated or to join another queen, 100% of subordinate queens migrated to the
dominant queen’s chamber--never vice versa. In total, these results suggest
that cooperative breeding is not a coercive strategy imposed by a dominant
breeder for her benefit only, but rather a self-interested strategy by
low-quality breeders to increase their survival and hence their lifetime
productivity—better to survive and reproduce a little than not at all. If a
dominant queen incurs no immediate cost or benefit to cooperative breeding, why
does she tolerate subordinates? This question must be addressed within a larger
ecological context that includes the super-fecund monogyne fire ant queens.
Given that the mean per capita rate of egg production for monogyne queens is
five-fold to ten-fold greater than that of polygyne queens, dominant polygyne
queens can produce larger colonies than monogyne queens only through
cooperative breeding. It matters not at all if the subordinate queens
contributing to colony size are their kin or not. In the final analysis,
cooperative breeding appears to be a rational, self-preservation strategy by
which marginal breeders (subordinates and
dominants) successfully compete against superior solitary breeders.
Arolia in termites (Isoptera): systematic comparison and functional
significance
Crosland, Michael W.J, N.Y. Su & R.H. Scheffrahn
Ft. Lauderdale Research and Education Center,
University of Florida, 3205 College Avenue, Ft. Lauderdale, FL 33314.
A comparative study of the presence or absence of arolia (=adhesive pads) on the tarsi of termite workers, soldiers and alates from the six major termite families was conducted. The results were contrasted with ants. Climbing ability was also compared among termites of different castes and ants. The results are discussed regarding possibilities of termite control and also in the light of the importance of paedomorphosis in the biology of termites.
Relatedness and population structure of tandem pairs during mating
flights of the termites Reticulitermes flavipes and R. virginicus
DeHeer, Christopher J. & Edward L. Vargo
Department of Entomology, North Carolina State University, Campus Box 7613, Raleigh, NC 27695
Analysis of colony and population genetic structure of Reticulitermes termites suggests that most colonies are initiated by alates which are unrelated to one another and have dispersed relatively far during mating flights. However, this conclusion relies on the assumption that mature colonies do not differ from incipient colonies in their genetic characteristics. This assumption could be violated if there is selection against either inbreeding or philopatry during the colony founding stage. In order to more directly assess the characteristics of potential new colonies, and thus the dispersal characteristics of alate termites, we collected pairs of both Reticulitermes flavipes (n=65 pairs) and R. virginicus (n=157 pairs) engaged in tandem running on days of mating flights. The collections of both species were distributed among several distinct locations spread across approximately one km. We genotyped both members of the pair at 12 microsatellite loci and utilized these data to infer the relatedness of individuals to their presumed colony-founding partner. We also applied a traditional population genetics framework to infer the dispersal capability of alate reproductives, and determined whether this differs between male and female alates.
Elekonich, Michelle M. & Stephen P. Roberts
Department of Biological Sciences, University of Nevada, 4505 Maryland Parkway, Box 4004, Las Vegas, NV 89154-4004
Adult honey bees undergo a process of adult behavioral development, spending their first 2-3 weeks working inside the constant environment of the hive which the
bees maintain at 33-35°C and 70-80% relative humidity. At about 3 weeks of age workers leave the hive as foragers who gather pollen and nectar and are exposed to a more variable environment. Heat shock proteins (Hsps) or stress proteins are expressed in response to heat, and various environmental stressors. Hsps function
as molecular chaperones to bind damaged proteins and refold them or tag them for degradation. We investigated both the heat shock response and constitutive heat
shock protein (Hsp70) expression in the brains and thoraces of individuals of different ages, behavioral groups and following exposure to various potential stressors.
Following 4 hours of heat stress at 43°C individual 9d old bees show increased Hsp70 expression (mRNA and protein) in brains but not thoraces with no induction
at hive temperature. In addition, constitutive Hsp70 expression varies with tissue type and behavioral state.
Colony founding strategies of Pogonomyrmex
salinus
Enzmann, Brittany
Department of
Ecology and Evolutionary Biology, University of California, Los Angeles, CA
90095
Colony founding is a
critical stage in the life histories of ants. It is the only period when mated
queens disperse to initiate nests that are geographically distinct from their
natal colony. Two defining aspects of
colony founding are 1) queen foraging (semiclaustral) versus no queen foraging
(claustral) during the cultivation of the first brood, and 2) solitary founding
(haplometrosis) versus group founding (pleometrosis). Some species of North American harvester ants (Pogonomyrmex, Myrmicinae) exhibit the
derived claustral strategy, while others have returned to an ancestral semiclaustral
condition. Similarly, some species
found in groups while others found alone.
Pogonomyrmex salinus is
widespread throughout the Northwestern United States, but little is known about
its colony founding strategy. I plan to
investigate whether queens of this species are claustral or semiclaustral
(obligate or facultative) and whether they are cooperative or solitary in
colony initiation. Information on
colony founding strategies of this species would not only increase our
understanding of its life history, but also provide general information for
investigation on the costs and benefits of one strategy over another.
A modeling approach to swarming
in honey bees (Apis mellifera)
Fefferman, Nina H. & Philip T. Starks
Biology Department, 120 Dana Hall, Tufts University, Medford, MA, 02155
Identifying the
mechanisms of colony reproduction is essential to understanding the
sociobiology of honey bees.
Although several mechanisms leading to the initiation of queen rearing – an
essential prerequisite to swarming – have been proposed, none have received
unequivocal empirical support. Here we model the main mechanistic hypotheses
(colony size, brood comb congestion, and worker age distribution) and show that
all proposed swarming triggers occur as a function of a colony reaching
replacement stability; the point at which the queen has been laying eggs at her
maximal rate. We also present a reproductive optimization model of colony
swarming based on evolutionary principles. All models produce results
remarkably similar both to each other and to empirically-determined swarming
patterns. An examination of the fit between the individual models and swarm-preventing
techniques used by beekeepers indicates that the reproductive optimization
model has a relatively broad explanatory range. These results suggest that an
examination into the behavioral correlates of a queen’s maximum egg laying rate
may provide a unified proximate mechanistic trigger leading predictably to
colony fission. Generating a predictive model for this very well studied animal
is the first step in producing a model of colony fission applicable to other
swarm founding eusocial animals.
Desiccation and starvation resistance of Nasutitermes
acajutlae when parasitized by an acanthocephalan (thorny-headed worm)
Fuller, Claire,1 Philip Rock2 & Taetia Phillips2
1Department of Biology, Murray State University, 334 Blackburn Hall, Murray, KY 42071
2Division of Science and Mathematics, University of the Virgin Islands, St Thomas, Virgin Islands 00802
The neotropical termite, Nasutitermes acajutlae, is parasitized by an acanthocephalan. This parasite is associated with behavioral changes that increase susceptibility of the termite to predation. We observed that parasitized workers survived longer outside of the nest than their unparasitized nestmates. We compared 1) survival of parasitized workers, unparasitized workers and soldiers from the same colonies under desiccation conditions (35 C); weight loss and survival in 2) workers from parasitized and unparasitized colonies under desiccation conditions and 3) under starvation conditions (31 C; 95% RH). Initial weight of individual termites was a covariate in all models. We found that parasitized workers survived significantly longer than unparasitized workers from their own or from unparasitized nests, but not longer than soldiers. Parasitized workers lost weight at the same rate as unparasitized workers, and died at a lower final weight. Under starvation conditions, workers from parasitized colonies (whether or not they were parasitized) lost weight and died sooner than termites from unparasitized colonies. Thus, parasitized termites had an advantage under conditions of desiccation but parasitized colonies have a disadvantage under starvation conditions. Longterm observations indicate that parasitized colonies are at a reproductive disadvantage compared with unparasitized colonies, suggesting that desiccation resistance is likely to benefit the parasite and not its host.
Cultivar parasite-inhibition and parasite host-attraction mediate the
outcome of host-parasite interactions in the fungus-growing ant symbiosis
Gerardo, Nicole & Ayeshah Castang (Cancelled)
Section of Integrative Biology, 1 University Station C0930,
University of Texas, Austin, TX 78712
Fungus-growing ants, their cultivated fungi, and the cultivar-attacking fungal parasite Escovopsis coevolve as a complex community. Here, through fungal interaction experiments, we show that Escovopsis strains are attracted to chemical signals produced by the host fungi that they normally attack and to closely related fungi but are inhibited by fungi distantly related to their typical hosts. The ecological importance of this parasite adaptation is highlighted through experiments showing that ant gardens infected with their typical versus atypical parasites have lower survival and growth both in the presence and the absence of the ants.
Multifaceted parental investment
and its effects on population-level sex allocation ratios in ants
Gilboa, Smadar & Peter Nonacs
Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095
One of the most fundamental decisions parents have is how
much to invest in each of their sons or daughters. The more a parent invests in each offspring, the fewer in total
it can produce.
The current dominant life-history paradigm for this trade off predicts
there is a specific "optimal" size of sons and daughters that follows
from an assumption that reproductive success is constrained only by the
parents’ ability to gather food. The
Optimal hypothesis further predicts that if parents’ abilities to provide for
offspring changes, they should change the number they produce and not the size
of their young. A recent alternative
view is the Multifaceted Parental Investment (MFPI) hypothesis. MFPI proposes that parents are often
constrained in reproductive decisions by more than resources. For example, parents experiencing unusually
good foraging can collect more food than their offspring can eat. MFPI predicts that such parents are brood
rather than food constrained and should make at least some of their offspring
larger than the optimal size. Although
the Optimal and MFPI hypotheses predict radically different parental strategies
for rearing offspring, they are not particularly easy to experimentally
differentiate. A key difference is that
the Optimal hypothesis predicts small size variation among offspring (e.g., a
normal or leptokurtic size distribution) and MFPI predicts large size variation
(e.g., greater than normal variation).
We present data here in three ant species that strongly support the MFPI
predictions as regards observed variation in offspring sizes.
Is there a
relationship between honey bee hygienic behavior and foraging ontogeny and
preference?
Goode, Katarzyna, Zachary Huber & Marla Spivak
Department of Entomology, University of Minnesota, 219
Hodson Hall, 1980 Folwell Ave., St. Paul,
MN 55108
The aim of this research was to determine the relationship between the expression of honey bee hygienic behavior and foraging ontogeny and preference. Because foraging and hygienic behavior are modulated by the sensitizing effects of octopamine, the behaviors may share neural processes and potential sites of modulatory convergence. Foraging ontogeny and preference can be predicted by a bees’ sucrose response threshold (the concentration of sucrose solution touched to the bee’s antenna that elicits proboscis extension). Hygienic and non-hygienic honey bees do not differ significantly in their responsiveness to sucrose; at each increasing sucrose concentration, there was no difference in the percentage of bees that extended the proboscis. Based on these results, we predict that there should be no differences between hygienic and non-hygienic bees in the age of first foraging, or in their tendency to collect nectar or pollen. Preliminary findings confirmed these predictions, and further trials are being conducted currently. The findings are important because they suggest that the foraging and hygienic behavioral routines are not interrelated tasks, and they are modulated by octopamine, the behaviors probably do not depend on similar neural substrates.
Normalized mutual entropy in biology: quantifying division of labor
Gorelick, Root1, Susan M. Bertram1, Peter R. Killeen2 & Jennifer H. Fewell1
1School of Life Sciences, Arizona State University, Tempe, AZ 85287
2Department of Psychology, Arizona State University, Tempe, AZ 85287
Division of labor is one of the primary adaptations of sociality and the focus of much theoretical work on self-organization. This work has been hampered by lack of a quantitative measure of division of labor that can be applied across systems. We divide Shannon’s mutual entropy by marginal entropy to quantify division of labor, rendering it robust over changes in number of individuals or tasks. Reinterpreting individuals and tasks makes this methodology applicable to a wide range of other contexts, such as breeding systems and predator-prey interactions.
Metabolism and foraging behavior in European and African honey bees
Grayson, Dina L., Alexander Keyel, Jennifer H. Fewell & Jon F. Harrison
School of Life Sciences, Arizona State University, Tempe, AZ
85287
Understanding how newly introduced organisms out-compete present fauna is fundamentally important for reasons ranging from the ecological to the financial. This is particularly true in the case of Africanized honeybees, which have spawned a wave of public apprehension preceding their spread. Some of the mechanisms proposed to contribute to their spread are a higher metabolic rate and greater foraging rate. This study determined whether African and European honeybees raised in the same hive environment differed in metabolism or foraging rate and whether the two characteristics are correlated. Our data showed that African workers possessed higher metabolic rates than European workers, but there were no differences in foraging rate between the two. In addition, there was no relationship between metabolism and foraging rate. However, both Africanized and European pollen foragers had consistently greater foraging rates than nectar foragers. These results indicate that the difference in metabolism between Africanized and European honeybees is consistent across studies, but that behavioral differences are context dependent.
Can the ecological constraints
model inform us about nesting tactics in a primitively eusocial wasp, Mischocyttarus mexicanus?
Gunnels, Charles W., IV
223 Bartram Hall, Department of Zoology, University of Florida, Gainesville, FL 32601
The
Ecological Constraints Model (ECM) has successfully identified a variety of
factors that can explain the evolution and expression of cooperative
breeding. As a part of the ECM, density
has been implicated in the expression cooperative breeding. In this study, I asked whether density could
explain the proportion of haplometrotic and pleometrotic foundresses in the
eusocial paper wasp, Mischocyttarus mexicanus. M. mexicanus is particularly appropriate to address this
issue because nests are initiated throughout the year and multiple nests are
initiated in the same tree (Sabal palmetto), making discrete estimates
of density in a natural environment possible.
During an 18-month census, I found that the proportion of haplometrotic
females was negatively correlated with density. This pattern was then examined experimentally by adding or
removing fronds from S. palmetto and then forcing nest
reinitiation. The percentage of
haplometrotic females decreased when fronds were removed (high-density
treatment) but remained unchanged in both low-density or control
treatments. The percentage of all
females emigrating from a tree and the average number of females per
pleometrotic nests were the same for each treatment. Together these data suggest that haplometrotic females joined
social nest in poor environments, which is consistent with of the ECM.
Heat shielding in honeybees: the
effect of this localized behavior on internal hive temperatures
Gurley, Kiersten L.,1 Adam J. Siegel1,
Brittany Kravets2, Nina H. Fefferman1, Aviva E. Liebert1
& Philip T. Starks1
1Department of Biology, Tufts University, Medford MA 02155
2Boston University, Boston, MA
Heat shielding is a method of thermoregulation used by the honey bee, Apis mellifera. Studies have shown that heat-shielding workers, who congregate on heated hive surfaces, are predominantly 12-to-14 days old and perform the behavior to protect late-stage brood. Using eight observation hives and heat lamps, we examined the ability of heat shielders to dampen the transfer of heat from outside to inside the hive. The presence of bees significantly reduced the transfer of heat, the number of shielders was positively correlated with this reduction, and the colony became progressively more efficient at dampening temperature increases. Additionally, by heating three different sized areas of hive wall (small, medium and large), we tested whether heat shielding was specific to localized heat stressors (i.e., to small areas) or was a general behavior to excessive heat in the brood-comb. When the entire brood-comb was heated bees exhibited evacuation-like behaviors, whereas with focused heat stress, shielding behavior was observed. Combined, our results suggest that heat shielding (1) is a behavior focused over localized heat-stressors, (2) is effective at dampening heat transfer, and (3) becomes more efficient over time. The complexity of the behavior suggests that heat shielding is an evolved, adaptive behavior.
Defensiveness of fire ant, Solenopsis invicta, workers increases
during colony rafting
Haight, Kevin L. & Walter R. Tschinkel
Department of Biological Science, Florida State University, Tallahassee, FL 32306-4370
Colonies of the fire ant, Solenopsis invicta, can survive flood conditions by forming a raft of workers that floats on the water’s surface until the flood recedes or higher ground is found. While rafting, colonies are totally exposed, and, deprived the safety of their subterranean nests, are left with only their stings for protection. As a result, rafting colonies may compensate for their increased vulnerability through an increase in defensiveness. We experimentally tested the hypothesis that such an increase would take the form of an increase in the amount of venom workers deliver per sting, since the pain and tissue damage caused by the venom (i.e. its repellency) is dose-dependent. In the lab, we assayed the venom doses delivered by S. invicta workers before and after flooding them from their nests with water. Workers delivered significantly higher venom doses while rafting than they did defending their nests pre-flood. Whereas observational data have suggested S. invicta workers increase their venom dose during periods of increased risk to colony assets (e.g. during the springtime production of sexuals), this data is the first to show such an increase experimentally.
Generating genetic markers and defining population structure of a
Caribbean termite (Nasutitermes acajutlae) using AFLP
Harris, Leslie,1 Elizabeth Walsh1 & Claire Fuller2
1Department of Biological Sciences, University of Texas, 500 W. University Ave., El Paso, TX 79902
2Department of Biology, Murray State University, 334 Blackburn Hall, Murray, KY 42071
Despite the importance of termites in tropical ecology, little is known about the genetic structure of their colonies. This study provides an in-depth analysis of the genetic make-up of nests of the neotropical termite Nasutitermes acajutlae on St. John, USVI. In this study we used Amplified Fragment Length Polymorphism (AFLP) to generate markers to assess N. acajutlae’s genetic population structure and to infer dispersal patterns. Termites were collected from 12 nests representing 5 distinct geographical points on St. John and two nests on a different island, St. Thomas. Using AFLP fingerprinting we were able to 1) generate many molecular markers for N. acajutlae, 2) determine that most genetic variation is found within colonies (~91%) rather than between populations (~9%), 3) establish that individual nests cluster as discrete groups, and 4) determine that nest differentiation was not based on geography. The mean percentage of individuals heterozygous per locus (H) ranged from 0.0679 – 0.0325. Percentage of polymorphic loci (P) ranged from 34% -52.5%. The FST value calculated across all loci was 0.0366+ 0.0023. AMOVA results indicate that there is significant difference in genetic structuring among termites within colonies and between populations but no significance difference among geographically isolated populations.
Heller, Nicole E. & Deborah M. Gordon
Department of Biological Sciences, Gilbert Hall, Stanford University, Stanford, CA 94305-5020
The Argentine ant, Linepithema humile, is a highly invasive, unicolonial species. Previous research has shown that Argentine ants form massive (1,000’s of km2)
associations of non-hostile nests, called supercolonies. However, little is known about space use and organization within these supercolonies. We mapped Argentine ant nests and trails in study plots for three years. We found evidence that supercolonies are differentiated into local colony networks, with groups of neighboring nests connected by above ground trails. The group of interconnected nests represents a cooperative sub-colony within the larger supercolony, that we call the “co-op”. The configuration and size of the co-op changes seasonally, with shifts in the location, number, size, connectivity, and spatial pattern of nests. In the winter, the co-op is contracted as nests are aggregated into certain areas. The same areas are used for winter aggregations year after year. By spring, winter aggregations are mostly abandoned and the co-op expands in spatial extent. The locations of nest sites in the summer and fall are more variable between years. Seasonal polydomy, shifts in the nest number and location between seasons, has been recorded in other ant species and may be an important component of unicolonial
behavior.
Reproductive isolation between hybridogenetic and non-hybridogenetic
forms of the harvester ant Pogonomyrmex rugosus
Helms Cahan, Sara1 & Glennis E. Julian2
1Department of Biology, University of Vermont, Burlington, VT 05405
2Department of Integrative Biology, University of Texas, Austin, TX 78721
Populations of the harvester ant Pogonomyrmex rugosus in the eastern portion of their range show an unusual genetically-based mode of caste determination not seen in western populations. In this “socially hybridogenetic” form, two distinct genetic lineages co-occur in the same population and interbreed to produce workers while pure-lineage offspring become reproductive queens. Previous genetic analyses of geographically distant hybridogenetic and non-hybridogenetic populations revealed strong allele frequency differences between each of the lineages and the non-hybridogenetic form, suggesting that gene flow between hybridogenetic and non-hybridogenetic populations may be reduced. We investigated small-scale patterns of gene flow between forms by sampling at approximately 10 km intervals along an 80 km transect between a known hybridogenetic population and a known non-hybridogenetic population in southeastern Arizona. Microsatellite markers indicated an abrupt geographic transition from the non-hybridogenetic to the hybridogenetic form, with no evidence of gene flow among any of the three genetic groups even at a site with co-occurring non-hybridogenetic and hybridogenetic colonies. Although lack of gene flow between hybridogenetic lineages is a direct consequence of genetic caste determination, it is likely that pre-mating mechanisms, such as variation in mating flight time, are responsible for reproductive isolation between the lineages and the non-hybridogenetic form.
Asexuality
in the fungus-growing ant, Mycocepurus
smithii
Himler, Anna,1 Ulrich Mueller,1 Eric Caldera,1 Hermogenes Fernandez-Marin2 & Boris Baer3
1Section of Integrative Biology, 1 University Station C0930, University of Texas, Austin, TX 78712
2Department of Biology, POB 23360, University of Puerto Rico, San Juan, Puerto Rico 00931
3Zoological Institute, Department of Population
Ecology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen,
Denmark
The
fungus-growing ant symbiosis is a model system to study evolution of
cooperation and conflict among mutualists and parasites, as well as speciation
and specialization. Investigation into
the role of cultivar switches driving ant speciation yielded an unexpected
result: Mycocepurus smithii appears
to reproduce strictly asexually (via thelytoky). Asexuality is unknown in all other 210 species of fungus-growing
ants. Only a few other ant species have been reported as facultative asexuals,
but none as an obligate asexual as M.
smithii appears to be. A
combination of natural history, genetic, behavioral and morphological data show
that M. smithii may represent a rare
case of a stable asexual lineage. A
large experiment in which 90 unmated female reproductives were switched to
different fungal cultivars documented strict asexuality over three generations. I explore the implications of frequent
cultivar switching and its association with parthenogenesis in this highly
unusual species. An asexual fungus-growing ant species whose widespread success
throughout the Neotropics is not only puzzling because of its apparent obligate
asexuality, but is doubly enigmatic because of its reliance on farming asexual
cultivar clones.
Relationship of fat content,
propagule numbers, and nest density to queen size in the queen size-dimorphic
ant Leptothorax longispinosus
Howard, Kenneth
Department of Zoology, University of Wisconsin, Madison, WI 53711
Social insects initiate new colonies either independently or dependently. In the independent-founding species, nest densities tend to be low, queens are large relative to the workers, have large energy stores, and are produced in high numbers; dependent-founding species occur in high densities, have queens that are similar in size to the
workers, have low energy stores, and are produced in low numbers. Species that exhibit both founding modes often have dimorphic-sized queens, in which small queens found dependently and large queens found independently. I measured nest densities, fat contents, and the number of female alates produced per nest in several queen-size dimorphic populations of the ant, Leptothorax longispinosus. Higher proportions
of both polygynous nests and small thorax queens were found at sites with high nest density than at low density sites. Large female alates were produced in significantly higher numbers per nest than small females at low density sites, but not at high density sites. Most nests produced females with percent fats typical of dependent-founding
species, regardless of female alate size. These results suggest that some characters usually correlated with each mode of colony founding can vary independently of one another, particularly when nest densities are high.
A new
paradigm of caste in social wasps
Hunt, James, H.1 & Gro V. Amdam2
1Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121
2Department of Entomology, 1 Shields Ave., University of California, Davis CA 95616
A new paradigm of caste in social wasps frames a new
understanding of the genesis and maintenance of
sociality in Vespidae. The paradigm also enables synthesis of various phenomena
in social wasps that heretofore have not been seen to have a common basis.
Application of the paradigm is not inherently limited to only wasps.
Hurd, Christine R.,1 Robert L. Jeanne1 & Erik V. Nordheim2
1Department of Zoology, University of Wisconsin, Madison, WI 53706
2Department
of Statistics, University of Wisconsin, 1210 W. Dayton St., Madison, WI 53711
Vespula colonies (Vespula spp.) are curious anomalies among flying social insects. Like other independent-founding species (Polistes wasps and Bombus bees), they reportedly show weak age polyethism and have only rudimentary task specialization. However, they attain colony sizes in the thousands, similar to swarm-founding species (Polybia wasps and Apis bees). Large colony size allows these species to partition labor into efficient, specialized worker groups for tasks such as water or pulp foraging, nest building, and food storing. This task partitioning is thought to reduce worker mortality risks and enhance information and material flows. If labor specialization and task partitioning can increase worker productivity in large colonies, why do Vespula species apparently lack them? Previous studies on Vespula labor were based on very small samples of workers. Our study documented the daily task performance of nearly 200 known-aged V. germanica workers. We found that size, weight, and ovarian condition were poor predictors of the age at which a worker first does a task and her rate of task
performance. We describe and quantify the variation in the task sequence workers move through as they develop. We confirm that V. germanica exhibits weak age polyethism and that only a small proportion of workers are task specialists. With the help of network theory, we suggest why V. germanica’s division of labor may not be as inefficient as otherwise suspected.
Biologically active compounds that elicit honey bee hygienic behavior
Ihle, Kate,1 Baldwyn Torto,2 Jim Tumlinson3 & Marla Spivak1
1Department of Entomology, University of Minnesota, 219 Hodson Hall, 1980 Folwell Ave., St. Paul, MN 55108
2Agricultural Research Service, Center for Medical, Agricultural, and Veterinary Entomology, USDA, 1600-1700 SW 23rd Dr, Gainesville, FL 32608
3Department of Entomology, Pennsylvania State University, University Park, PA 16802-3508
We have hypothesized that honey bee hygienic behavior (the uncapping and removal of diseased and parasitized brood) is mediated by olfactory cues. However, we have not conducted direct tests to determine if biologically active compounds emitted from diseased brood actually elicit the behavior. We collected volatile chemicals on polymeric adsorbent from healthy brood and from brood infected with the fungal disease, chalkbrood. GC-MS analysis of the volatiles showed significant qualitative differences between the volatiles of healthy and diseased larvae. Two chalkbrood disease-specific components were identified in the volatiles of diseased larvae and their identities confirmed by GC-MS co-injection analysis with authentic compounds. In bioassays, the chalkbrood disease-specific components were introduced into newly capped cells containing healthy brood to determine if the chemical stimuli elicited uncapping and removal by the bees. In addition, we performed associative learning trials using the proboscis-extension reflex, to determine if individual hygienic bees could detect and respond to the disease-specific components at lower concentrations than non-hygienic bees.
Michener’s paradox revisited
Jeanne, Robert L.,1
Andrew M. Bouwma,1 & Erik V. Nordheim2
1Department of Entomology, University of
Wisconsin, 1630 Linden Drive, Madison, WI 53711
2Department of Statistics, University of Wisconsin, 1210 W. Dayton St., Madison, WI 53711
In 1964 Charles Michener published a paper entitled “Reproductive efficiency in relation to colony size in hymenopterous societies,” in which he showed that, for most species analyzed, the larger the colony, the lower the productivity per female. He concluded that the pattern implied the existence of social mechanisms that cause higher efficiency per female the smaller the group. This pattern, known as “Michener’s paradox,” suggests that selection should favor smaller, more efficient colony size, even to the point of eliminating sociality, if not countered by advantages of large colonies. Michener’s paradox has been widely accepted as a general pattern among social Hymenoptera, yet has been subjected to few direct tests.
In his analysis of per-capita productivity in several species of tropical swarm-founding social wasps, Michener did not control for the influence of ontogeny on colony size and productivity. We show for two species of swarm-founding wasps that when stage of colony development is held constant, colony size has no influence on per-capita productivity. We suggest that the pattern Michener reported was due to ontogenetic effects and to species differences. Thus, there is no evidence for intrinsic social mechanisms that reduce efficiency per female in larger colonies of these wasps.
Jeanson, Raphael,1 Penelope H. Kukuk2 & Jennifer H. Fewell1
1School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501
2Division of Biological
Sciences, University of Montana, Missoula, MT 59812-4824
A central question in the study of insect societies concerns the emergence of division of labor. Among the different models of division of labor, the threshold model postulates that task specialization can emerge from initial inter-individual differences in propensity to perform a task. The requirements of this variance-based model are likely to be present of the origin of sociality and may account for the emergence of division of labor in early social evolution. However, behavioral interactions among the group members are also likely to shape early social organization and contribute to the genesis of task specialization. In this study, we focused on the early stages of nest construction in solitary and communal Halictine bees. The excavation performance of single bees and the social interactions among pairs of solitary or communal bees were assessed. We also recorded the individual behaviors during nest construction for pairs of solitary or communal bees. Pairs of solitary bees exhibited a higher level of task specialization than pairs of communal bees. Using a set of behavioral rules derived from these experiments, we developed a numerical model to determine the respective contribution of inter-individual behavioral asymmetry and social interactions in the emergence of task specialization.
Coevolution between social parasites and hosts: evidence for the red
queen?
Johnson, Christine A. & Joan M. Herbers
Department of Evolution, Ecology & Organismal Biology, The Ohio State University, Aronoff Laboratory, 318 W. 12th Ave., Columbus, OH 43210
Protomognathus (= Harpagoxenus) americanus and Temnothorax duloticus are two slave-maker ant species that use Temnothorax curivspinosus as their primary host in central Ohio. We examined experimentally the concomitant impact of each slave-maker species alone and combined on the social biology of T. curvispinosus by comparing the demographies of colonies maintained in field enclosures. Enclosures contained colonies of one slave-maker species and five T. curvispinosus, one P. americanus, one T. duloticus and ten T. curvispinosus or five T. curvispinosus housed in hollowed wood dowels lined with glass tubing to facilitate observation. Every two weeks for several months, adult and immature individuals of all castes and sexes were censused. In my talk, I will present preliminary results of the experiment and their implications for parasite-host coevolution.
Judd, Timothy M. & Mathew P. Fasnacht
Department of Biology, Southeast Missouri State University, Cape Girardeau, MO 63701
In social insect colonies, macronutrients such as proteins and carbohydrates tend to be preferentially distributed to individuals that need them. For example, individuals that grow receive a higher portion of protein gathered by the colony. However, many micronutrients such as calcium, potassium and sodium have also been shown to be important for growth and development in insects. Little work has been done to examine the distribution of these nutrients within a colony. We tested to see if micronutrients are distributed unequally within colonies of the termite Reticulitermes flavipes. Colonies were fed artificial diets containing controlled level of minerals. Individuals were examined to see if these micronutrients were stored preferentially by those individuals that grow (workers) to those individuals that do not grow (soldiers).
Why be a hybrid? Behavioral
differences in hybrid and non-hybrid Pogonomyrmex rugosus
Julian, Glennis E.1 & Sara Helms Cahan2
1Department of Integrative Biology, University of Texas, Austin, TX 78721
2Department of Biology, University of Vermont, Burlington, VT 05405
The discovery of genetic caste determination in populations of hybrid P. rugosus has raised questions about how it evolved and is maintained. Theoretically, genetic caste determination should be costly since many queen-destined eggs are wasted when a colony is not in the reproductive stage. However, this phenomenon appears widespread and stable. It is possible that hybrid workers have selective adaptations that give them an advantage. We compared behavioral characteristics of hybrid colonies with co-existing non-hybrid P. rugosus colonies to establish any behavioral differences between types. We measured mass aggression toward a simulated vertebrate predator, using carbon dioxide as a stimulant. Additionally, we measured intra-specific and inter-specific recognition and aggression with individual workers. Lastly, we set up direct competitive foraging and aggression experiments between hybrid and non-hybrid colonies. Hybrid colonies reacted faster and more aggressively when stimulated by carbon dioxide than the non-hybrids. However, hybrid and non-hybrid workers show equal amounts of low aggression towards non-nestmates, and escalated aggression towards each other. In a foraging competition, non-hybrid colonies dominated foraging seed piles in 80% of interactions. In summary, there are distinct behavioral differences between hybrids and non-hybrids, but whether there is a selective advantage in having hybrid workers is not clear.
Abundance,
diversity, and biomass of ants in Florida’s upland ecosystems
King, Joshua R.
Department of Biological Science, Florida
State University, Tallahassee, FL 32306-4370
The empirical relationships among species richness, relative abundance, and body size in different habitats may help to elucidate the factors responsible for existing patterns of community structure. Ant assemblages were thoroughly sampled in five upland ecosystems in north-central Florida. A total of 37, 961 ants of 94 species were weighed to determine biomass. Patterns of species richness, relative abundance, relative biomass of foraging workers, species co-occurrence patterns, size ratios of species, and species turnover between ecosystems were quantified.
Species richness and species occurrences were greatest at intermediate body sizes. Constant spacing of body sizes among species at local and regional scales suggests that interspecific competition among ecologically similar species may be responsible for these unimodal relationships. Species richness (Si) within biomass classes was related to the number of species occurrences (Oi) as Si = Oi0.4 at the regional scale. Within size classes abundance distributions of size classes were similar power functions at the regional scale. Both relationships were similar although less robust at local scales, which may be a result of abiotic specialization by species. A general rule of resource division (e.g. non-overlapping niches), together with similar minimum populations sizes adequately determines these relationships between species richness and abundance.
Klein, Barrett
Department of Ecology, Evolution and Behavior; Section of Integrative Biology, University of Texas, Austin, TX 78712
The purpose of hitchhiking, in which minima leaf-cutter ant workers ride plant loads carried by their larger colony mates, has been presumed to involve protection against parasitoids, either animal or fungal. It has been reported that in order to reduce the parasitism of major workers by phorid flies, hitchhiker ants are recruited as bodyguards. Additionally, it has been suggested that hitchhikers clean fungus from the surface of plant loads before they are incorporated into the colony’s susceptible fungal gardens. Examining the spatial and temporal dynamics of hitchhiking in Atta cephalotes and A. colombica in Costa Rica and Panama supported neither defense against parasitic flies or fungi as an exclusive explanation for hitchhiking. Temporal and spatial hitchhiker frequencies did not correlate with reported phorid fly presence. Also, replication of an observational study did not support the presumed preparation of plant material by hitchhiking ants.
Hitchhiking densities
positively correlated with plant fragment surface area on which hitchhikers
traveled, and not with size class of the laden worker. I detected no discernible rhythm of
hitchhiker frequency, although I did find interspecific differences in
hitchhiking, and mapped individual hitchhiking across space and time.
Biogeography
and ecological impacts of ant decapitating flies (Diptera:Phoridae) in the
Madrean Archipelago
LeBrun, Edward G.1 & Brian V. Brown2
1Division
of Biological Sciences, Ecology Behavior and Evolution Section, University
of
California San Diego, 9500 Gilman Drive, San
Diego, CA 92093-0116
2Natural
History Museum of Los Angeles County, 900 Exposition Boulevard, Los
Angeles, CA 90007
A wide diversity of flies in the family Phoridae parasitize adult worker ants. In some systems, these flies act as keystone species, influencing the structure of local ant assemblages far out of proportion to their abundance. They exert this influence by altering the behavior of dominant ant species thereby altering the competitive dynamics of the ant assemblage as a whole. The Madrean Archipelago is one of the most northern locations where phorids become a prominent feature of local ant assemblages. Thirty-one species of ant-parasitizing phorids are known from the Sky Island mountain ranges. Twenty are undescribed. The host species and some natural history information are known for 13, and detailed ecological studies have been conducted on 2. We present experimental evidence from work in the Chiricahua Mountains demonstrating that these phorids reduce the behavioral dominance of their host ant, dramatically altering its ability to capture food resources. This eliminates the linearity of the assemblage dominance hierarchy and alters the form of the assemblage tradeoff between the ability to dominate and to discover food resources, promoting co-existence in the ant assemblage. In addition, we summarize what is known about the identity, distribution, and natural history of ant-phorid associations in this area.
Triploid females and diploid
males in the model wasp genus Polistes
Liebert, Aviva E.,1 Rebecca N. Johnson,2
A. Sumana,1 Ghislaine T. Switz1 & Philip T. Starks1
1Department of Biology, Tufts University, Medford MA 02155
2Evolutionary Biology Unit, Australian Museum, 6 College Street, Sydney, NSW, 2000, Australia
Although the sex-determining mechanism in the Hymenoptera
generally results in haploid males and diploid
females, diploid males can be produced when individuals are homozygous at the
sex-determining locus. These abnormal males are either sterile or produce
presumably sterile triploid offspring; thus their production is extremely
costly to the colony. We report the occurrence of triploid females in three
species of Polistes, which suggests
that male diploidy is more common in this genus than previously thought. We
also present evidence for lack of recognition of both diploid males and
triploid females in P. dominulus,
resulting in a delayed cost of diploid male production for two generations.
These findings have implications for several important areas of Polistes research, including invasion
biology, sex ratio investment, and reproductive skew theory.
Direct
assessment of queen fertility and lack of worker suppression in the paper wasp Polistes dominulus
Liebig, Jürgen,1 Thibaud Monnin,2 & Stefano Turillazzi3
1Department of Behavioral Physiology and
Sociobiology, Biozentrum, Am Hubland, 97074 Würzburg, Germany
2Laboratoire d'Écologie CNRS UMR 7625, Université Pierre et Marie Curie, 7 quai Saint Bernard, 75005 Paris, France
3Dipartimento di Biologia Animale e
Genetica, Universita degli studi di Firenze, Via Romana 17/19, 50125 Firenze,
Italy
Assessing a
conspecific’s potential is often crucial to increase one’s fitness, e.g. in
female choice, contests among rivals or reproductive conflicts in animal
societies. In the latter helpers benefit from accurately assessing the
fertility of the breeder because it largely determines their inclusive fitness.
The fertility of the breeder could be assessed through chemical correlates of
reproductive activity. We show that it can also be assessed by monitoring the
breeders’ reproductive output. In the paper wasp Polistes dominulus, we
mimicked a decrease of the breeder’s fertility by regularly removing brood from
cells of the comb. This manipulation triggered ovarian development and
egg-laying by many workers. The extent of worker egg-laying was correlated with
the amount of empty cells, which suggests that the latter represent a reliable
cue workers use to assess the fertility of the queen. If her fertility is low
indicated by many empty cells they switch to own reproduction. Brood abundance
can be monitored when workers perform regular brood care. Although the queens
were not manipulated they did not prevent workers from reproducing.
Nevertheless, when workers reproduce the queen secures a near reproductive monopoly
by destroying worker-laid eggs, whereas workers destroyed comparatively few
queen-laid eggs.
Direct and indirect genetic
effects on gyne, worker, and male mass in the ant Temnothorax curvispinosus
Linksvayer, Timothy A.
Indiana University, Department of Biology, 1001 East 3rd
Street, Bloomington, IN 47405
The phenotype of an individual is determined by its genes (direct genetic effects) and its environment. When the environment is influenced by social partners, genes expressed in these social partners also influence an individual’s phenotype (indirect genetic effects). In this case, the environment has a genetic basis and can evolve. In social insects, the social environment is determined by interactions with parents, sibling adults, and sibling brood. For example, maternal care, care by sibling adults, and competition with sibling larvae, all affect the social environment of a developing larva. Thus, a variety of indirect genetic effects, as well as direct genetic effects, and interactions among all of these effects, influence traits expressed by social insects and are likely to impact the evolutionary dynamics of these traits. I report the preliminary results of a study designed to determine the relative importance of these varied genetic effects on gyne, worker, and male mass, in the acorn ant Temnothorax (=Leptothorax, subgenus Myrafant) curvispinosus. Mass is an important phenotype in ants and is expected to be influenced by both direct and indirect genetic effects.
Population level sex ratio expression in Aphaenogaster
rudis (Formicidae):
observed variation and its implications
Lubertazzi, David & Eldridge Adams
Department of Ecology & Evolutionary Biology, University of Connecticut, Storrs, CT 06269
Ants have played an important role in the field of sex ratio research for many decades, serving as a focal taxon for studying sex ratio questions. My research is designed to critically examine some of what is known, and what is not well understood, about sex ratio expression in ants through careful study of the common Connecticut woodland ant, Aphaenogaster rudis. I will present population sex ratio data collected from two field populations of this species for two consecutive years. The data show significant variation between years. This result highlights the fact that proximate factors can strongly influence sex ratio expression and reinforces our need to better understand the role that non-genetic factors play in sex ratio expression.
Colony nutritional status and its influence on the learning ability of
worker honey bees (Apis mellifera L.)
Mattila, Heather R.,1 Gard W. Otis1 & Brian H. Smith2
1Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
2Department of Entomology, Ohio State University, Columbus, OH 43210-1220
The connection between nutrition and learning is not well understood for invertebrates in general and insects in particular, although it has been demonstrated often in vertebrates. For honey bees (Apis mellifera L.), learning is an integral part of a worker’s ability to operate successfully in a changing environment. We examined the influence of pollen availability during larval development on aspects of adult worker honey bee learning within a proboscis extension reflex paradigm.
The ecological stoichiometry of a tropical ant community
McGlynn, Terrence
Department of Biology, University of San Diego, 5998 Alcala Park, San Diego, CA 92110
The
relative proportions of macronutrients and micronutrients in the soil are major
predictors of animal density and trophic structure. In an earlier study in a Costa Rican tropical wet forest, I found
that C:P and C:N were significant predictors of density for most taxa, but not
for ground-dwelling ants. As a result of their colonial habits and
trophic diversity, stoichiometric effects upon ants may be reflected in the
demographics and community structure rather than density. To test this hypothesis, I returned to the
same forest to intensively sample colonies of leaf litter ants from eighteen
sites across an edaphic gradient.
The global population genetic structure of the little fire ant Wasmannia
auropunctata
Mikheyev, Alexander S.
Section of Integrative Biology, 1 University Station C0930, University of Texas, Austin, TX 78712
Native to much of Central and South America, the little fire ant Wasmannia auropunctata has been rapidly spreading throughout the world. In the invasive range W. auropunctata has been frequently linked with drastic reductions of ant diversity, as well as with attacks on vertebrates. I sequenced mtDNA to identify the likely source populations within its large native range. Phylogenetic analysis revealed at least three separate source populations of W. auropunctata, as well as the possible existence of two cryptic sympatric subspecies. Much of Caribbean region is inhabited by a clade of ants sharing very similar mtDNA haplotypes, suggesting the possibility of multiple introductions or high levels of gene flow in that area. This clade has also invaded much of the Pacific. Another clade based in South America has invaded French-speaking Gabon and New Caledonia. These findings suggest phylogenetic information is necessary for making meaningful comparisons between populations in the native and invasive ranges, as well as for comparing differences among W. auropunctata populations in the native range. In this spirit, I conducted a phylogenetically independent test of McGlynn’s (1999) hypothesis that invasive populations of W. auropunctata have smaller worker than native populations, which it appears they do.
Mueller, Ulrich, G.
(Cancelled)
Section of Integrative Biology, 1 University Station C0930, University of Texas, Austin, TX 78712
This paper
encourages investigations into the microbial ecology of social insects and argues
that the microbiological and molecular-genetic techniques for studying
social-insect/microbe interactions are technically not that difficult. The
paper will explore (1) how social insects have evolved mechanisms to take
advantage of associations with microbes in their nests to derive physical,
nutritive, biochemical, sanitary, and antibiotic benefits; (2) whether social
insects with long-lived nest (e.g., many ants and termites) experience
particularly intense coevolutionary interactions with microbe communities
developing in their nests; and (3) what mechanisms stabilize mutualistc
associations between social insects and microbes.
Two
principles emerge from an analysis of the evolutionary dynamics between
microbes and social insects:
(1)
Many interactions with microbes
evolve according to the “Mafia Principle”: because it is impossible to avoid
antagonistic interactions with microbes (i.e., it is cost-prohibitive to
eliminate or police all elements of the Mafia), social insects may as well
cooperate with a subset of microbes and use them to take care of the really
detrimental ones (i.e., allow some elements of the Mafia to operate and use
them to hold in check the most dangerous elements of the Mafia). Cooperation with select microbes thus
emerges from generalized conflict with microbes.
(2)
Cooperative interactions between
social insects and the faster-evolving microbes probably originate as byproduct interactions, but some of
these interactions become eventually stabilized by directed reciprocation, which operates via two separate mechanisms:
partner choice and partner fidelity feedback (Sachs et al.
2004). (i) Partner choice (symbiont choice) is a choice mechanism involving
discrimination against undesirable (“uncooperative”) partners. (ii) Partner fidelity is an automatic
feedback mechanism in which uncooperative partners ultimately curtail their own
fitness by harming partner fitness.
Partner choice and partner fidelity often operate jointly, though they
can act independently. Future empirical
work should evaluate social-insect/microbe mutualisms as to whether they are
maintained via partner fidelity, partner choice, or both mechanisms. Most social insects probably express
elements of choice favoring associations with certain microbes in their nests.
References:
Sachs, J.L., U.G.
Mueller, T.P. Wilcox, J.J. Bull. 2004. The Evolution of Cooperation. Quarterly
Review of Biology 79: 135-160.
Reproductive
skew, assured fitness returns and the evolution of cooperation in Hymenoptera
Nonacs, Peter
Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095
Reproductive skew models are used to predict the
interactions of cooperative breeders, while the evolution of cooperation,
itself, has been predicted through models of assured fitness returns (otherwise know as headstart models). I show here that the latter models can be
considered as a special case of the more general reproductive skew models. Data from several polistine wasp species
that exhibit facultative cooperation in colony initiation support the
prediction that subordinate wasps can have higher inclusive fitness than
solitary foundresses. This is true,
however, only for full sisters and under conditions where foundresses are in
conflict with their workers over sex ratios.
Thus, reproductive skew models may help answer why facultative
eusociality appears to evolve more often in haplodiploid Hymenoptera relative
to other taxonomic groups. These
models, however, do not appear to be sufficient to explain other common
patterns observed in eusocial Hymenoptera such as cooperation between distantly
related or unrelated individuals.
Brain parasites in eusocial paper wasps (Hymenoptera: Vespidae, Polybia
aequatorialis)
O’Donnell, Sean,1 Benjamin Land,2 & Teresa Jones3
1Neurobiology and Behavior Program and Department of Psychology, University of Washington, Seattle, WA 98195
2Neurobiology and Behavior Program, University of Washington, Seattle, WA 98195
3Department of Psychology, University of Texas, Austin, TX
Solitary sociality: social behavior in an allegedly “solitary” bee
Prager, Sean & Miriam H. Richards
Department of Biological Sciences, Brock University, 500 Glenridge Ave, St. Catharines, Ontario, L2S 3A1 Canada
The large carpenter bees, of genus Xylocopa, have traditionally been classified as solitary, exhibiting no social behavior, or potentially communal. Recent work has shown that this is not the case in some species within this genus. Our work on Xylocopa virginica, the species native to eastern North America, suggests even more complex social interactions. Multiple researchers have noted instances of multiple X. virginica females utilizing a common nest entrance. Our studies use nest excavation, dissection and video observation, to examine the behavior of these bees in Southern Ontario. These studies suggest that not only are these females socially co-existing within a single nest, but that they are engaging in an unusual form of social interaction where some females refrain from both reproduction and foraging.
Pratt, Stephen
Department of Ecology and Evolution, Princeton University, Princeton NJ 08544
Animals face an inherent trade-off between the speed and accuracy of decision-making, and may favor one or the other in different contexts. I examined the mechanisms underlying this tradeoff during collective nest site choice by emigrating colonies of the ant Leptothorax curvispinosus. Colonies can choose the better of two nest sites, but the speed and accuracy of their performance depend on the urgency of the move. I compared the behavior of colonies in a situation of high urgency—the old nest was experimentally destroyed—with a situation of low urgency—the old nest was of poor quality, but still habitable. Under high urgency, ants completed their emigrations over two times faster, but were significantly more likely to move entirely or partly into the inferior of two alternative new sites. Experiments in progress are examining the emergence of this colony-level tradeoff from context-dependent adjustments in the behavior of individual ants. I am focusing on previously discovered decision rules that allow workers with knowledge of only one site to contribute to the collective choice. This promises to show how individuals with purely local information and no central control can not only generate functional global behavior, but also optimize it according to context.
Diversity and nest density
of non-leafcutting, fungus growing ants (Formicidae, Myrmicinae, Attini) in an
Amazonian Terra Firme rainforest and a
nearby agroforestry area
Rabeling, Christian,1 Manfred Verhaagh2 & Marcos V.B. Garcia3
1Section of Integrative Biology, Patterson Laboratories, University of Texas, Austin, TX
78712
2State Museum of Natural History, Erbprinzenstr. 13, D-76133 Karlsruhe, Germany
3Embrapa Amazônia Ocidental, Manaus, Brazil
The
fungus-growing ants, Attini, comprise the well-known leaf-cutting species that
defoliate living plants and the "primitve" groups that nourish their
fungus gardens with debris collected from the leaf litter. The ecological role of the
"primitive" species is not understood, but it is possible that they
have strong influence on decomposition and nutrient cycles in tropical forest ecosystems.
As a first step to investigating this ecological role, we documented the attine
species richness and nest density in an agricultural area and compared it to a
rainforest habitat. In the agricultural
habitat we found significantly lower attine species richness but high nest
densities of three species (75% of them were Mycocepurus smithii, 14% Trachymyrmex
relictus and 11% M. goeldii).
Soil-nesting attines in general move nutrients into lower soil layers by moving
organic debris into their nest chambers. Therefore, these three species may
play an important ecological role in soil physics and chemistry of Amazonian
agroforestry systems.
Founding
stage of Acanthomyops (Formicidae)
Raczkowski, Joe (Cancelled)
Department of Evolution, Ecology & Organismal Biology, The Ohio State University, Columbus, OH 43210
The founding stage of Acanthomyops (Formicidae) is often assumed to involve temporary social parasitism of Lasius species, even though evidence for this remains limited. Here I present work to date on the founding stage of Acanthomyops.
Dominant
species and the abiotic environment shape ant species density and community
structure in Darlingtonia
fens and adjacent forests
Ratchford, Jaime, S.,1 Nathan J. Sanders,2
Sarah Wittman,3 Aaron Ellison,4 Erik Jules1 &
Nick
Gotelli3
1Department of Biological Sciences, Humboldt State University, Arcata, CA 95521
2Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996
3Department of Biology, 211 Marsh Life Science Building, University of Vermont, Burlington, VT 05405
4Harvard University, Harvard Forest, PO Box 68, Petersham, MA 01366
A major aim of ecology is to understand the factors that influence the distribution and abundance of species across heterogeneous landscapes. In this study, we examined how a suite of factors influence the diversity and structure of ant communities in Darlingtonia fens and adjacent forests in the Siskiyou Mountains following the Biscuit Fire of 2002. We systematically sampled ants in fens and adjacent forests at 16 sites, 8 of which burned during the fire. In total, we collected 25 species. Ant community structure differed substantially between fens and forests. Total ant species density depended on habitat type and the interaction between habitat type x burn history. Species density was consistently higher in forests than in fens. Fire history had no effect on species density in forests, but species density in burned fens was >50% higher than in unburned fens. Ant species richness, across habitat types, was correlated with several factors: total plant species richness, average temperature and percentage of open canopy at a site, and the abundance of Tapinoma sessile, a competitively dominant species. Taken together, these results show how both biotic and abiotic factors interact to determine the distribution and abundance of ants in heterogeneous landscapes.
Behavioral
reactions to trans-2-butyl-5-heptylpyrrolidine in Solenopsidini ants
Roesel, Christopher,1 Rachelle Adams1 & Tappey Jones2
1Section of Integrative Biology, 1 University Station C0930, University of Texas, Austin, TX 78712
2 Department of Chemistry, Virginia Military Institute, Lexington, VA 24450
Chemical communication in ants has been studied intensely for several decades, and new compounds are still being discovered. Many of these compounds play an important role in communication, such as trail laying, alerting behaviors, recruitment, species recognition, and as a repellent. It has been shown that mixtures of compounds as well as concentration can induce dramatically different behaviors, and by synthesizing and assaying these different compounds we can begin to recognize how behavior and chemical signals are associated. With the intention of breaking down this complexity, we began by examining one prominent alkaloid produced by Megalomyrmex modestus to elucidate its function. The Solenopsidini tribe consists of 13 known genera, of which three (Solenopsis, Megalomyrmex, and Monomorium) are known to produce 2,5-dialkylpyrrolidines. Specifically, the alkaloid trans-2-butyl-5-heptylpyrrolidine is known to be used by Solenopsis species to repel competitors at food baits and to enable brood thievery with little conflict. This alkaloid is also a prominent compound found in Megalomyrmex modestus, however it is unknown how this species utilizes this compound. Using a synthetic 2-butyl-5-heptylpyrrolidine in an isomer ratio of 2:1 cis to trans, we studied the behavioral responses induced by this alkaloid by presenting it in various concentrations to several Solenopsidini species.
Rossi, Benjamin, H. & Peter Nonacs
Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095
Sexual coercion is a potent force responsible for sexual dimorphism in many species. Males of the alfalfa leafcutter bee (Megachile rotundata) use a mating strategy that resembles sexual coercion. In a previous study, male body size and difference in body size was significantly correlated with the rate of interactions, when the male and female are in physical contact. I seek to determine the effect of body size on mating success. In one experiment, males and females were paired up and videotaped for one hour each. Videos were analyzed to determine if the larger males attempted to mate more often and for longer durations. There was no relationship found between absolute and relative male size and rate/duration of mating attempts, though there was a significant correlation between size and rate/duration of other male-female interactions. These data help determine the importance of body size for the success of male coercion, and suggest directions for future laboratory and field work.
Sanchez, Leticia1 & James Diffendorfer2
1University of Colorado, Boulder, Dept. of
Ecology and Evolutionary Biology, Campus
Box 334, Boulder, Colorado 80309
2Illinois
Natural History Survey, 607 East Peabody Drive, Champaign, Illinois 61820
The Index of Biological Integrity (IBI) was first developed as a quick measure for the quality of freshwater lake and stream systems. Recently, it has been adapted for terrestrial use. The IBI involves scoring abiotic and biotic factors that are deemed indicators and summing them to determine the magnitude of disturbance to the ecosystem. In this study, disturbance was measured as the percent or relative exotic cover of invasive grasses. Exotic species cover includes foliar cover of all non-native species, most of which are herbaceous (i.e. grasses and forbs). The most common exotic grasses include 3 annual species of Bromus (brome) and 2 species of Avena (wild oat), while the most common exotic forbs include 3 species of Erodium (filaree). The presence of these grasses can result in the homogenization of Coastal Sage Scrub (CSS). Ants are an ecologically diverse group, encompassing many functional roles of an ecosystem. As such, they may be good indicators of disturbance to these habitats. This study used a subset of data collected while attempting to determine an IBI of the CSS ecosystems in Southern California. Southern California has been called a hotspot of biodiversity due to the high amount of endemism and species diversity. However, with the growing presence of anthropogenic disturbances such as commercial and residential development, and the introduction of exotic species, the diversity of this area is in danger of being significantly reduced. Data was collected over a two year period by the use of pitfall traps. We determined the relationship between ant diversity and species richness with percent relative exotic cover. Richness at the genera level was also compared to percent relative exotic cover. The use of genera over species compares ant diversity at the functional level.
Molecular phylogenetics and phylogeography of ponerine ants
Schmidt, Chris A.
Department of Entomology, Forbes Building #36, Room 410, University of Arizona, Tucson, AZ 85721-0036
Ponerine ants (Ponerinae, sensu Bolton 2003) are a diverse and conspicuous component of tropical faunas, and typically exhibit primitive social and behavioral attributes. Despite their value as potential models for studying social evolution, the relationships among the major ponerine lineages and their phylogeographic history are almost completely unknown. Past reliance on morphological characters to discern ponerine relationships has proven fruitless, perhaps due to a rapid early radiation of major lineages or frequent morphological convergence. I present a preliminary molecular phylogeny for the Ponerinae, utilizing nuclear protein-coding genes to elucidate tribal and generic relationships. Among other results, the large genus Pachycondyla is found to be clearly polyphyletic, illustrating the utility of molecular data for resolving obscure relationships and the need for taxonomic revision of the subfamily. Preliminary results of a phylogenetic dating analysis are also presented, and the implications for ponerine phylogeography are discussed. These results will ultimately help reconstruct the sequence of evolutionary, migratory and geological events that resulted in the present diversity and distribution of the subfamily, and will lay the groundwork for future taxonomic revisions and studies of ponerine prey specialization, morphological convergence and social evolution.
Horned lizards
and Pogonomyrmex harvester ants: the enigmatic relationship between the
world’s most toxic ants and fat lizards (and how the relationship might
transcend historical sympatry)
Schmidt, Justin O.
Southwestern Biological Institute, 1961 W. Brichta Dr., Tucson, AZ 85745
Pogonomyrmex ants are large, conspicuous, and possess the most toxic known arthropod venoms to mice. Their algogenic and toxic venoms appear to explain why worker ants have no meaningful vertebrate predators – except for lizards in the genus Phrynosoma. These broad, slow moving lizards are ant specialists, with a particular preference for Pogonomyrmex ants. The question arose: how could these lizards consume prodigious numbers of their spicy prey when other vertebrates could not? It turned out that they evolved blood serum proteins that specifically neutralize the lethal toxins in Pogonomyrmex venom. Pogonomyrmex (and their sister taxon Ephebomyrmex) are distributed from Canada to Southern Argentina and Chile with a large gap in Central America. Phrynosoma are distributed from Canada to Mexico, with no evidence that they were ever distributed in South America. I tested the hypothesis that harvester ant species that likely evolved in the absence of selection pressure from Phrynosoma would possess less toxic venoms than their North American relatives, and that their venom lethality would not be neutralized by the serum proteins of Phrynosoma. Both hypotheses were falsified by data from experiments with Phrynosoma cornutum from Arizona and Ephebomyrmex cunicularius from Argentina. The data from these experiments and their implications are presented.
The vibration signal and juvenile
hormone titers in worker honey bees, Apis
mellifera
Schneider, Stan S.,1 Lee A. Lewis1 & Zachary Y. Huang2
1Department of Biology, University of North Carolina, Charlotte, NC 28223
2Department of Entomology, Michigan State Univ., East Lansing, MI 48824
We examined the association between the vibration signal and juvenile hormone (JH) titers of honey bees by comparing vibrated recipients and non-vibrated control workers that had been matched for age, colony of origin, and time of collection. Recipients collected at the moment they received vibration signals (0-min bees) did not have higher JH titers compared to controls. Therefore, a worker’s initial JH level did not influence its likelihood of receiving signals. In contrast, JH titers in workers collected 15-30 min after receiving vibration signals were slightly, but significantly higher than those of controls monitored for the same amount of time. These trends were consistent among colonies, despite the fact that we collected different age ranges of workers and observed pronounced variation in JH titers within and between the different groups of bees. Thus, over a broad age range of workers the vibration signal may contribute to elevated JH levels, and this effect does not occur because recipients have higher titers at the moment they receive signals. Because JH affects response thresholds in honey bees, increased titers elicited by the vibration signal may allow the signal to influence the performance of a variety of tasks in different worker age groups.
Seal, Jon, N.
Department of Biological Science, Biology Unit I Building, Florida State University, Tallahassee, FL 32306-4370
Leaf-cutting ants make clear choices of leaves. Previous work implicitly assumed that preferences reflect the
optimal needs of the ants and symbiotic fungus; however, few experiments
demonstrate a link. This project uses
the higher attine Trachymyrmex septentrionalis as a model system to
address this problem. In this study, 24
colonies were collected from the Apalachicola National Forest in the spring of
2003. Preferences were based on
substrates that foragers in field colonies collect and were thus ‘natural’
substrates. Substrate preferences were
then determined in pairwise trials and then the colonies were randomly assigned
to one of two treatment groups that corresponded to unpreferred and unpreferred
substrates. In each preference category
there were two different substrates and each colony received only one type of
substrate. Feedings commenced until
colonies produced sexuals. Preferences
were remarkably fixed; foragers in all colonies consistently preferred catkins
from oak trees and caterpillar frass and did not prefer flowers and
leaves. While preferred substrates
generally lead to large fungus gardens and high levels of ant biomass, there is
significant variation among the substrates within each preference. Therefore
preference and ant production are not correlated. Work in progress includes quantifying the amount of fungus in
these gardens.
Siegel, Adam J.,1 Julia Hui,1 Rebecca N. Johnson,2 Philip T. Starks1
1Department of Biology, Tufts University, Medford MA 02155
2Evolutionary Biology Unit, Australian Museum, 6 College Street, Sydney, NSW, 2000, Australia
Heat-shielding (defined as stationary bees congregating on a heated hive wall) is used by
honey bee workers to protect developing brood from localized heat stress. We
examined the behavior in response to heat and
cold stress. We also recorded stationary and
moving workers found on the hive wall and brood-comb. Observations suggest
that stationary bees on the brood-comb shield the brood from localized heat and
cold stress: after temperature-stress, stationary bee quantity under the
stressor significantly increased. A uniform response from stationary bees on
the hive wall was not observed: stationary bee number increased after heat
stress but decreased after cold stress. Movement of bees on both the hive wall
and brood comb decreased in response to cold stress. Movement of bees on brood
comb decreased after heat stress, but increased on the hive wall after heat
stress. Although potentially an artifact, this latter result raises the
possibility that bees are creating currents to dissipate heat and/or are
absorbing heat and moving it to non-sensitive areas. Our data indicate that
‘heat-shielding’, as previously defined, is a category within a broader
response of honey bees to localized temperature stress: Apis mellifera appear to
respond adaptively to all localized temperature stressors.
Assured fitness returns and social flexibility in the sweat bee Megalopta
genalis
Smith, Adam, R.,1 William T. Wcislo2 & Sean O’Donnell3
1Department of Psychology, University of Washington, Seattle, WA 98195
2Smithsonian Tropical Research Institute, Box 2072, Balboa, Ancon, Republic of Panama
3Neurobiology and Behavior Program and Department of Psychology, University of Washington, Seattle, WA 98195
Assured fitness returns models for the evolution of sociality emphasize the value of maintaining parental care until brood emergence. We previously used the facultatively social Neotropical halictid bee Megalopta genalis to show that defense against ant predation is part of parental care. Thus, even in a mass-provisioning species, group living may be selected for as a means to insure that at least one individual survives to defend to the dependent brood. If so, two further predictions should be met: social nests should suffer less predation than solitary nests, and nestmates left behind after experimental removals of other bees should continue defending the brood.
We show that brood in social nests do indeed enjoy higher survival than brood in solitary nests. Also, social nests have at least equal, and possibly higher, per-capita productivity than solitary nests. And primary foragers are smaller than reproductives. Queen removal experiments showed that foragers did remain at the nest to continue defending brood. These data are all consistent with helpers accruing indirect fitness via assured fitness returns. However, after queen removal, foragers also developed their ovaries and began laying eggs, showing that helping behavior can also be a means to direct fitness via nest inheritance.
Sex and the colony: a tale of how
the Florida harvester ant, Pogonomyrmex
badius, invests in sex
Smith, Chris R. & Walt R. Tschinkel
Department of Biological Science, Florida State University, Tallahassee, FL 32306-4370
The fitness of any long-lived organism is determined, in large part, by how it allocates resources into growth and reproduction in any given cycle. Mature colonies of the Florida harvester ant, Pogonomyrmex badius, only invest into reproduction in the late spring, but invest continuously into growth throughout the year. Both the capacity to reproduce as well as the amount invested into reproduction are determined by the size of the worker population. Colonies invest proportionately (i.e., isometrically) into reproduction, although are variable in how they partition their investment into male and female sexuals. The onset of sexual production in spring appears highly synchronized allowing all mature colonies to have sexuals ready to participate in the first nuptial flight. However, nuptial flights occur over the course of a month, and sexual pupae are still present in the colony when flights begin.
Color polymorphism in a leafcutter ant
Solomon, Scott, E. & Ulrich G. Mueller
Section of Integrative Biology, 1 University Station C0930, University of Texas, Austin, TX 78712
Color is not considered to be a very reliable taxonomic character, yet numerous subspecies, geographical races and varieties have been described using color. One such example is that of the leafcutter ant, Atta cephalotes, which has a great deal of intraspecific diversity; indeed, several subspecies have been described based primarily on color. We investigated whether A. cephalotes isthmicola, which was described primarily based on color, is in fact distinct from other conspecific varieties. The results suggest that at a local level, there is some genetic differentiation between color morphs. However, at larger geographical scales, this pattern is confounded. Furthermore, the color polymorphism appears to be a plastic trait in some populations, reinforcing the notion that color is not a good taxonomic character in these ants.
Localized fever in a super-organism:
infection-induced temperature up-regulation in colonies of Apis mellifera (Hymenoptera: Apidae)
Starks,
Philip T.1 & Rebecca N. Johnson2
1Department
of Biology, Tufts University, Medford, MA, 02155
2Evolutionary
Biology Unit, Australian Museum, 6 College Street, Sydney, NSW, 2000, Australia
Honey
bees (Apis
mellifera L.) have been shown to up-regulate brood-comb temperature in
response to colony-wide infection with the fungal pathogen Ascosphaera apis, the agent that causes chalkbrood disease.
Previous reports estimate the temperature increase at ~0.5ºC. We collected data
from four treatment and two control colonies maintained within a temperature
controlled chamber. Here we show that the post-infection temperature increase
is variable within the brood-comb (Range: 0.22-1.04ºC), with the largest increase
expressed in the periphery where the larvae are most susceptible to A. apis. Colony size also influenced
fever production, with smaller colonies increasing temperature more than larger
colonies. Because A. apis is
heat-sensitive, because the temperature increase was largest over the most
susceptible brood, and because colonies that could least afford to lose workers
(i.e., small colonies) mounted the largest temperature response, we argue that
fever is an adaptive response to chalkbrood disease.
Ant predation and biological
control of the root weevil, Diaprepes
abbreviatus, in Florida citrus: field
manipulations
Stuart, Robin J., Ian W. Jackson & Clayton W. McCoy
Department of Entomology and Nematology, University of Florida, IFAS, CREC, Lake Alfred, FL 33850
The root weevil, Diaprepes abbreviatus (L.), is a major pest of Florida citrus. When neonate larvae hatch in the citrus canopy and drop to the soil surface before burrowing down to the roots for feeding, they are extremely vulnerable to ant predation. We manipulated ant populations in citrus groves using granular ant baits to determine the relationship between ant population levels (measured with baits) and predation pressure on neonates (measured by exposing lab-reared neonates to field predation). Our results indicate a strong correlation between ant population levels and predation pressure, and reinforce the view that ants are important biological control agents of Diaprepes neonates.
Sumana, Annagiri,1 Tauheed Zaman,1 C.M. Orians,1 D. Richardson2 & Philip T. Starks1 (Cancelled)
1Department of Biology, Dana Laboratories, Tufts University, Medford MA 02155
2Department of Chemistry, Willams College, Williamstown MA 02167
Paper wasps are known to possess
cuticular hydrocarbons (CHC) that signify nestmate status, reproductive caste
and matriline. Research indicating this has collected CHC samples from the
head, thorax, abdomen, or wing. As no single body part has been used, this
research makes the implicit assumption that CHC are homogenous across the body.
We tested this assumption using 36 Polistes
dominulus wasps from 9 colonies by studying the CHC using gas chromatographic
techniques. We also observed antennation patterns, as antennae are the likely
means through which CHC are perceived. Our data indicate that CHC profiles are
not homogenous across the body. Individual body segments, however, are
sufficient to identify nestmate status and reproductive caste. Our data also
show that individuals contain unique CHC profiles, which could be used to
maintain a linear dominance hierarchy. Interestingly, antennation patterns were
dependent on dominance status: subordinates antennate abdomens while dominants
antennate heads and thoraces. The implications of our findings are discussed.
Chemical cues and philopatry in the primitively eusocial paper wasp, Polistes
dominulus (Hymenoptera: Vespidae)
Switz, Ghislaine, Annagiri Sumana, Anne Berry & Philip T. Starks
Department of Biology, Dana Laboratories, Tufts University, Medford, MA 02155
Polistes dominulus is a well-studied paper wasp whose overwintered females are known to be philopatric. Prior to nest construction, spring foundresses often return to their natal nest site and perch on their natal nest. Recent evidence indicates that these females continue to recognize and discriminate in favor of the natal nest after landmark and gross morphological cues are removed. Because Polistes wasps recognize their nests, and because cuticular hydrocarbons facilitate nestmate discrimination, we hypothesize that natal nests retain colony-specific hydrocarbon cues from the previous year. To test this hypothesis, we obtained two hydrocarbon samples from 17 nests: one sample in the fall of 2003 and one sample in the spring of 2004. We analyzed these samples using gas chromatography. Despite novel hydrocarbon presence in both fall 2003 and spring 2004, we show that colonies retain more hydrocarbons than expected by chance (one sample sign test, p=0.0042). Our results raise the possibility that relatively stable and shared hydrocarbons are used by overwintered foundresses to recognize the natal nest.
Honey bee waggle dancers produce volatile chemicals
Thom, Corinna,1 Harald E. Esch,2 David C. Gilley3 & Judith Hooper1
1ARL Division of Neurobiology, University of Arizona, Gould Simpson Bldg, POB 21077, Tucson, AZ 85721
2Department of Biology, University of Notre Dame, Notre Dame, IN 46556
3Carl Hayden Bee Research Center, 2000 E. Allen Road, Tucson, AZ 85719
The
waggle dance of honey bee (Apis mellifera L.) foragers communicates to nest mates the location of a
profitable food source. Tactile and
acoustic signals appear to play a role in waggle-dance communication, but we
still have much to learn about the mechanisms by which waggle dancers attract
and convey information to potential recruits (Dyer, 2002). We investigated whether waggle dancers
produce a volatile chemical signal using Solid Phase Micro Extraction (SPME)
sampling and a gas chromatograph coupled to a mass spectrometer (GC/MS). We found four compounds that were present in
much higher amounts on waggle-dancing foragers than non-dancing foragers
returning from the same unscented food source.
The production of non-floral volatile compounds by waggle-dancing honey
bees suggests that olfaction may play an important role in attracting and/or
conveying dance information to potential recruits.
A socially-enforced visual signal of quality in the paper wasp Polistes
dominulus
Tibbetts, Elizabeth1 & James Dale2
1Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA
and Center for Insect Sciences & Division of Neurobiology, University of Arizona,
Tucson, AZ 85721, USA
2Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
Many organisms use signals of
quality to communicate information about aspects of their relative phenotypic
and genetic constitution. Signals of
quality require high and differential costs to remain honest (i.e. prevent
low-quality cheaters from exploiting any fitness benefits associated with
communicating high quality). Some
quality signals appear cheap to produce, so researchers have long been
interested in what type of cost maintains signal honesty. One hypothesis is
that signals may impose social costs incurred through repeated agonistic
interactions with other individuals. We demonstrate social costs in a
previously undescribed quality signal: the highly variable black facial
patterns of Polistes dominulus
wasps. Facial patterns strongly predict
body size, a correlate of dominance.
Independent of their relationship with size, facial patterns also
predict social dominance. Moreover, in
staged contests between pairs of unfamiliar wasps, subordinate wasps with
experimentally altered facial features (‘cheaters’) received considerably more
aggression from the dominant than did sham controls, indicating that 1) the
facial patterns are signals and 2) dishonest signalling imposes social
costs. Complex visual signals have been
found in other wasps; Polistes fuscatus
have visual signals of individual identity.
Therefore, visual signalling among social insects may be richer and more
varied that previously anticipated.
Division of labor and nutrition: a comparative genomics perspective
Toth, Amy L.1 & Gene E. Robinson2
1Program in Ecology and Evolutionary Biology, University of Illinois, Urbana-Champaign, IL 61801
2Department of Entomology, Neuroscience Program & Program in Ecology and Evolutionary Biology, University of Illinois, Urbana-Champaign, IL 61801
Foraging is associated with a decline in stored lipids in a number of social insect species. Our previous work has shown this for the honey bee (Apis mellifera), and our more recent findings indicate that experimentally induced nutritional deprivation (starvation or pharmacological treatment) cause both an early onset of foraging and upregulation of foraging-related genes in the brain. Based on all these results we hypothesize that the connection between nutritional depletion and food searching behavior is conserved in eusocial lineages. We are currently testing this hypothesis by determining whether non-foraging and foraging individuals share common patterns of brain gene expression in honey bees and the paper wasp Polistes metricus. In Apis, an advanced eusocial species, the comparison is between worker nurses and foragers, while in Polistes, a primitively eusocial species, it is between dominant and subordinate individuals. The comparison is based on genes already identified from candidate gene and microarrays analyses of nurse and forager honey bees. In this talk we will present results on the effects of experimentally induced nutritional changes on behavior and brain gene expression in Apis and preliminary results from Polistes.
Similarities and differences between social insect and social shrimp societies
Toth, Eva
Virginia Institute of Marine Science, 1208 Greate Road, Gloucester Point, VA 23062
While most eusocial
animals live in terrestrial ecosystems, social sponge-dwelling shrimp of the
genus Synalpheus represent the only
eusocial taxon that lives in aquatic environments. Since eusocial shrimp have
been discovered recently and because studying them in aquatic conditions
represent a challenge, not much is known on the ecology and behavior of this
group. Comparing shrimp to terrestrial eusocial animals can enable us to gain
more insight on important factors all social animals share. In this talk I will
highlight recent results that deal defense behavior and possible morphological
castes in social shrimp communities.
The organization of foraging in the fire ant, Solenopsis
invicta
Tschinkel, Walter, R.
Department of Biological Science, Florida State University, Tallahassee, FL 32306-4370
The fire ant, Solenopsis invicta, defends an absolute territory against its neighbors, and derives all its food from within this territory. For 90% of the distance between food finds and the nest, foragers move within foraging tunnels that reach all parts of the territory. Scouts and recruitable workers are not based within the nest, but are stationed throughout the territory in these foraging tunnels. As a result, recruits usually appear at baits within a few minutes, far too quickly to have traveled from the nest. When foragers were marked at baits and recaptured the next day, 90% were located in the territory, and only 10% in the nest, suggesting that foragers spend 90% of their time away from the nest, returning only to deliver food to workers in the nest. Foragers marked and released at one point in the territory were recaptured throughout the territory the next day, indicating that route fidelity is lacking. The proportion of the total worker population that forages decreases as colonies grow. In small colonies, about 65% of workers forage (i.e. can be recruited to baits in the territory), whereas in large colonies only about 30% forage. Simultaneously, the mean size of foragers increases, with probable effects on the diet of the colony. Overall, the foraging system of this fire ant is decentralized throughout its territory, allowing rapid recruitment to food, and probably contributing to territory maintenance and defense.
Flight of the honey bee: an aerodynamic analysis of hovering in
variable-density atmospheres
Vance, Jason T., Michelle M. Elekonich & Stephen P. Roberts
Department of Biological Sciences, University of Nevada Las Vegas, Las Vegas, NV 89154-4004
In honey bees, tasks such as foraging, undertaking and
colony thermoregulation require the ability to vary and perhaps approach the
limits of flight muscle metabolism and performance. Here we study the limits of flight muscle power production of
honey bee foragers. Flight kinematics
(3-D; 6000 fps) were determined while bees
hovered in air (21% O2/ 79% N2) and heliox (21% O2/79%
He), the latter having a density 1/3 that of air. The heliox condition effectively increased the workload of
hovering flight as demonstrated by increased wing-stroke amplitude and
wing-beat frequency, and possibly initiated a “clap and fling” strategy during
the back-to-forestroke transition, a point in the wingstroke when the wings
actually contacted each other. Furthermore, wake-recapture and rotational effects may also
be contributing to the additional lift necessary to maintain hovering flight
under increased workloads. This
study represents one of the most detailed kinematic and aerodynamic analyses
ever for a hovering insect and provides insight to the metabolic and power
reserve capacities that honey bees rely on for critical behavioral tasks.
The breeding system and population genetic structure of the subterranean
termite Reticulitermes grassei in southern France
Vargo, Ed,1 Christopher J. DeHeer,1 Magdalena Kutnik2 & Anne-Geneviève Bagnères2
1Department of Entomology, Campus Box 7613, North Carolina State University, Raleigh, NC 27695-7613
2Institut de Recherche sur la Biologie de l’Insecte, Université François Rabelais, Tours,France
Previous work on the subterranean termite Reticulitermes grassei in Europe has suggested there is geographic variation in colony and population structure of this species, with populations in southwestern France consisting of “open” colonies in which a lack of nestmate recognition leads to poorly-defined colony boundaries, whereas populations in the southern Iberian Peninsula consist of “closed” colonies which are distinct and vigorously defended. We re-examined this issue by assessing colony and population genetic structure in three French populations of R. grassei using eight polymorphic microsatellite loci. Contrary to previous reports, we found that colony boundaries were well-defined. Most colonies contained the offspring of multiple, highly related replacement reproductives (extended families), whereas some contained the offspring of a single pair of reproductives (simple families), and the proportion of such colonies varied across populations (Range = 0 – 44%). Populations also showed variability in the degree of inbreeding in simple families and the numbers of reproductives within extended families based on F-statistics. Values for simple families indicated only slight levels of inbreeding in one population and high levels in another. Values for extended families were consistent with having upwards of one hundred pairs of replacement reproductives in some populations, while in other populations such colonies appeared to contain fewer than 10 pairs.
Factors influencing queen adoption in the Argentine ant Linepithema
humile
Vasquez, Gissela & Jules Silverman
Department of Entomology, 3321 Gardner Hall, Box 7613, North Carolina State University Raleigh, NC 27695
Adoption of new queens is widespread in polygynous ant species. Adoption decisions may be made based on relatedness of colony members to new queens, queen competition for colony resources, and the effects of queen adoption on colony survivorship and productivity. To better understand the dynamics of queen adoption in introduced populations of the polygynous Argentine ant, we compared acceptance of nestmate and non-nestmate queens in queenless and queenright colonies. More non-nestmate queens were adopted by conspecific queenless vs. queenright colonies. Queen cuticular hydrocarbon profiles were compared between colonies, and also between adopted (nestmate and non-nestmate) and host queens. Offspring production by non-nestmate and nestmate queens after colony adoption was recorded using DNA markers. Results are discussed in terms of cuticular hydrocarbon similarities between adopted queens and adopted queen contribution to colony productivity.
How do bees in a honey bee swarm know when
their group decision among nest sites is completed?
Visscher, P. Kirk1 & Thomas D. Seeley2
1Department of Entomology, University of California, Riverside, CA 92521
2Department of Neurobiology & Behavior, Cornell University, Ithaca, NY 14853
A swarm of honey bees (Apis mellifera) chooses among multiple discovered sites, and usually achieves unanimity in dancing for a single site, then takes off and flies to it. How do the bees recognize that the decision is complete and that it is time to initiate the preparation for their swarm’s move to their new home?
We evaluated two hypotheses: consensus sensing, the scouts noting when all the bees performing waggle dances are advertising just one site; and quorum sensing, the scouts noting when one site is being visited by a sufficiently large number of scouts. We found that a consensus among the dancers was neither necessary nor sufficient for the start of worker piping (the prepare-for-takeoff signal), but that a buildup of 10-15 or more bees at one of the nest boxes was consistently associated with the start of worker piping. In a further test of quorum-sensing, we found that delaying the formation of a quorum of scout bees at a swarm’s chosen nest cavity, while leaving the rest of the decision-making process undisturbed, delayed the start of worker piping and takeoff of the swarm. These results refute consensus-sensing and provide strong support for the quorum-sensing hypothesis.
Response of Reticulitermes termites and their symbiotic protozoans to volatile plant
oils
Waller, Deborah, A.
Biology Department, Old Dominion University, Norfolk, VA 23529
Little is known about the factors that regulate feeding in termites. This study examined the effects of volatile plant oils on subterranean termites and their symbiotic enteric protozoans. Termites might be expected to react negatively to plant chemicals that are harmful to the gut symbionts. In choice tests, several essential oils were identified that appeared to be attractive to Reticulitermes (Isoptera; Rhinotermitidae) workers and soldiers; in no-choice tests, these chemicals were antifeedant and/or lethal to the termites. Protozoan numbers in termites exposed to these oils did not differ from those in unexposed, control termites, however.
Zelikova, Tamara
Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309-0334
I investigated the effects of habitat type (forest versus open field) on seed dispersal by ants in tropical dry forests of Costa Rica. I also assessed the quality of different ant species as seed dispersal vectors within different habitats. I compared the latency of response, dispersal distance, seed carrying time, dispersal destination, and the effects of habitat on dispersal services between several species of ants within the genus Pheidole and Ectatomma. Latency of response was shorter in the open field than in the forest. Both average dispersal distance and average seed carrying time were greater in the forest than in the open field. Seeds were more likely to remain untouched by ants in the open field than on the forest floor. Interspecific comparisons yielded that ants in the genus Pheidole were better seed dispersers because they recruited heavily to seeds, dispersed further, and were more efficient seed movers. Ectatomma riudum did not recruit workers to seed baits and carried seeds much shorter distances, frequently dropping seeds in route to their nests. Based on these observations, I conclude that life histories of disperser ants play an important role in determining the fate of seeds that fall to the forest floor.