The overarching theme of my research is the evolution and ecology of social adaptation. I use ants to explore diverse topics such as host-parasite relationships, mutualisms, foraging ecology, community ecology, reproduction, and caste evolution.

The ecology and evolution of castes in harvester ants

The evolution of caste is a hallmark of advanced sociality and is a criterion for the most derived state of sociality, eusociality. Many insect societies have gone beyond mere reproductive division of labor and further subdivided tasks among the non-reproductive worker caste. Of the approx. 60 species of Pogonomyrmex harvester ants the presence of 3 distinct morphological castes (gyne, minor and major) within colonies has evolved twice independently. In North America, the Florida harvester ant, P. badius, and in South America, P. coarctatus, have both evolved polymorphic workers. I use a variety of tools, from genetics to field experiments, to explore the ecology and evolution of female polymorphism.

The organization and regulation of reproduction in harvester ants

Reproduction in social insects involves ultimate and proximate factors acting on both the individual and colony. The social Hymenoptera have become model systems for testing the importance of both of these levels of selection, individual and colony, as well as antagonism between them. I use the Florida harvester ant to study reproductive investment and allocation. In particular, I address how allocation into both growth and reproduction (including sex ratios) vary according to the role of both external and stored resources.

The evolution of polyandry and mating syndromes in harvester ants

Most harvester ant nests are headed by a single queen (monogyny) who has mated with multiple males (polyandry). Why polyandry evolves is a matter of much debate, but through it the colony increases its genetic diversity which may yield benefits through the division of labor, disease resistance, diploid male production, etc. With detailed observations of the mating syndromes of many harvester ant species, myself and colleague Kirk Anderson (University of Arizona), are working at describing the variation in polyandry that is observed in the genus (from 1-2 mates up to 27).

Optimal foraging

Ants have been used in many studies on the optimality of foraging, but none of these account for the many non-food objects brought back to the nest. I believe that an understanding of how and why these objects are returned to the nest is central in our understanding of “optimal” foraging, especially since many species of ant collect so many objects (e.g., the harvester ant, P. barbatus, can have millions of pebbles on top of its nest, all the result of single foraging trips). To understand foraging I examine the tradeoff between food vs. object retrieval, and the interdependence of tasks within the colony. The interdependence of tasks is part and parcel of multi-level selection on foraging in ant colonies, which is often ignored when considering the optimization of any single task.