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O'Donnell Lab Research Projects

Prospective students can contact me (so356 "at" drexel.edu) for more information.

The brief descriptions below present a sample of the active research projects in my lab.

 

THERMAL PHYSIOLOGY and ECOLOGY: MICROHABITAT, ELEVATION and PERFORMANCE LIMITS

Neotropical ants (Formicidae) experience a wide range of thermal environments: they forage and nest in diverse microhabitats from above- to below-ground, day and night, and some species span wide elevational ranges. We are exploring how these omnipresent tiny animals respond to their thermal environments by measuring individual, colony, population and species differences in thermal physiology and social thermal homeostasis.

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BRAIN PLASTICITY, DEVELOPMENT AND BEHAVIOR

Neuroecology: Evolution of brain architecture in social insects

We are using statistical methods that account for the effects of evolutionary relatedness (phylogeny) on correlated evolution among traits to test whether brain architecture has evolved along with social structure in paper wasps. Paper wasp phylogeny is well characterized at the genus level, and paper wasp exhibit a wide array of social complexities. Species vary in colony size, mode of colony founding, nest architecture, and in the degree of queen-worker caste differentiation. We are exploring how behavioral and developmental factors, such as nest architecture and caste determination, have affected the evolution of the amount of investment in functionally distinct brain regions. Brain size and female caste (queen vs. worker) are associated with brain structure differences.

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Individual and caste differences in brain architecture

The main goal of this project is to assess whether neural plasticity in the brain, particularly in the mushroom bodies, plays a functional role in social wasp workers' task performance. In addition to measuring gross brain region volumes, We use stereological microscopy techniques to measure the volume of functionally distinct regions of paper wasp brains, and test whether the size of different brain regions corresponds to individual differences in age, social rank, and task performance. We use Golgi staining methods to quantify changes in dendritic processes of brain neurons that may underlie changes in neuropil volume.

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 DIVISION OF LABOR IN INSECT SOCIETIES

How dominance interactions and nutritional physiology regulate social insect division of labor

Dominance is based on aggressive social interactions that influence individuals' access to resources. It has long been recognized that dominance among female social wasps plays a role in governing the separation between reproductive roles (queens) and sterile, helping roles (workers). I am working on several genera of independent-founding (Polistes and Mischocyttarus) and swarm-founding (Polybia) social wasps to assess how dominance interactions within the worker force influence task performance and non-reproductive division of labor (polyethism). I am particularly interested in the role of adult nutrition in governing social roles.

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ARMY ANT COMMUNITY ECOLOGY

Behavior and ecology of army ants: how climate, elevation, and habitat alteration affect the biology of these top predators

Collaborators: Mike Kaspari (Univ. of Oklahoma), Anjali Kumar (AAAS fellow), John Lattke (Univ. Central de Venezuela), Scott Powell (George Washington University)

Army ants (Ecitoninae) are mobile insect societies that conduct mass hunting raids across and under forest leaf litter. They are top predators, and as such likely have an major impact on forest animal community structure. Army ants are akin to such spectacular elements of the Neotropical fauna as jaguars and harpy eagles. We have compared army ant community structure across latitudinal and elevational gradients to assess factors that affect their density, diversity, and ecological impact on prey and commensals. Results from this work suggest that army ant raids occur at astoundingly high rates in lowland primary wet forests, on the order of one raid/square meter/day! Our main approach has been to sample army ant density and diversity at different sites using standardized sampling protocols. By comparing latitudinally separate sites, we showed that army ant species composition changes significantly over regional scales, with implications for their commensals and parasites, including antbirds. Surveys across elevational gradients showed that above ground raiders and subterranean species differ in their responses to forest clearing and elevation.

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NETWORK MODELS AND GROUP DECISION MAKING 

Analyzing how communication affects task allocation

Collaborators: Dr. Susan Bulova, Dr. Michael O'Connor

A review of the role of social communication in allocating workers among tasks showed that social insects employ diverse modes of communication to coordinate labor with their colonies. The details of these communicative mechanisms, of the structure of social groups, and of worker responses to social information may all shape the ways that colonies allocate workers among different jobs. We developed an individual-based simulation model to explore how characteristics of social groups (number of group members), details of communicative interactions (the strength of effects on receivers), and cognitive mechanisms (forgetting about past interactions) can influence the recruitment of group members to a new task.

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POPULATION AND SOCIAL GENETICS 

Population genetics of Neotropical army ants (Ecitoninae)

Collaborators and students: Dr. Anjali Kumar (AAAS fellow), Dr. Kerry Naish (Univ. of Washington Aquatic & Fishery Sciences), Tom Soare (Univ. of Washington Animal Behavior PhD student)

Our behavioral and ecological data show that army ants can be affected by changes in elevation, and by human disturbances such as forest clearing and forest fragmentation. Temperature and other abiotic gradients appear to play a strong role in army ant distributions and movement patterns. However, army ant species differ in their responses to habitat variation. We are particularly interested in differences between above-ground raiding species (Eciton burchellii) and underground raiding species (Labidus coecus). We are scoring both nuclear (microsatellites) and mitochondrial DNA markers of genetic variability to quantify population genetic structure in army ants, with the aim of identifying ecological variables that affect population genetic structure. The microsatellite data, which include both maternal and paternal contributions to colony genetics, will complement the patterns seen in the maternally inherited mtDNA markers. Maternal inheritance patterns may be especially relevant in these ants: they have wingless queens, and colonies reproduce by splitting the work force, part of which literally walks away with a new queen. Males are winged and potentially move genes over longer distances. Our microsatellite data confirm that army ant queens have very high mating frequencies.

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AVIAN COMMUNITY AND BEHAVIORAL ECOLOGY

Habitat variation effects on birds attending army ant raids in tropical montane forests and Bivouac checking by birds that attend army ant raids

Collaborators: Nicole Arcilla, Nicola Clayton (Cambridge University), Anjali Kumar (AAAS fellow)

A diverse fauna of birds attend army ant raids in montane tropical forests. The birds obtain food at the swarm raids by capturing small animals that flee from the advancing army ants. The montane attendants are particularly interesting because few or no true antbirds are present in montane forests. We are exploring the possibility that high-fidelity or obligate ant following behavior has evolved in some montane bird species. Montane army ant following birds are affected by elevation and forest fragmentation.

Among the birds that attend montane army ant raids are several species of long-distance migrants that breed in North America. These include species of thrushes, warblers and vireos. We are using relative abundance estimates from previous mist net studies to assess whether some migrants are specialized as army ant followers.

Some birds that specialize as army ant followers engage in elaborate behavior called bivouac checking. These birds visit the temporary resting clusters of a series of army ant colonies in the early morning, apparently assessing the ant's raid activity for that day. We are interested in the expression of this behavior by some montane birds that are not in the true antbird family (Thamnophilidae). We are also interested in the cognitive implications and challenges of bivouac checking for the birds.

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Developing a non-nutritive sweetener as a human-safe insecticide

Collaborator: Dr. Daniel Marenda

Following up on a school science fair project by Dan's son, we found the sweet polyalcohol erythritol is effective as an insecticide when ingested by insects. Starting with lab fruit flies, the work has expanded to testing on other insects (several species of ants, mosquitoes, aphids, and field tests on berry crop pests). We hold a US patent for use of erythritol in insect control. We are excited about the potential for contributing new safer methods of insect control in a range of systems and contexts.

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