The Evolution of Cooperation and Cooperative Breeding in Ant Queens
Queens facing off!
Why unrelated individuals should cooperate remains a significant puzzle in evolutionary biology. An important problem in determining its evolutionary causes is that cooperation in extant taxa evolved in the distant past under unknown ecological conditions. However, intraspecific geographic variation in queen breeding systems in the ant Veromessor pergandei provides a powerful system for empirical tests of why cooperation and cooperative breeding evolve. In this common and widely distributed ant of the Mojave and Sonoran Deserts of North America there are three distinctly different breeding systems distributed in different geographic regions: one where queens establish a new colony alone, a second where queens establish a new colony in groups, but later fight until one survives, and a third where queens form groups, do not fight, and persist long-term to breed cooperatively. Our recent studies have determined how different social systems are distributed across the species’ range and comparative studies have tested how natural selection has acted to result in different phenotypes. Moreover, because V. pergandei has a single contiguous geographic range, different social systems are in direct contact across the desert landscape.
Contemporary and ongoing evolution across contact zones allows for direct tests of
which environments favor one social form over another.
Pogonomyrmex and their nest. Image source: Bugguide.net
A defining feature of social insects such as ants, bees, and wasps is differentiation of individuals into specific castes, yet little is known about the types and number of genes responsible for initiating divergent developmental pathways. Although in virtually all eusocial species it is the environment, rather than genetic predisposition, that determines who develops into a queen, several populations of harvester ants use a genetically-based mechanism for determining reproductive caste. Non-hybrid offspring are genetically unable to develop into workers, presumably due to homozygosity at one or more caste loci. This offers a unique opportunity to use standard genetic mapping techniques to identify genes responsible for initiating alternate caste phenotypes. We are using genomic methods to identify Single Nucleotide Polymorphism (SNP) markers across the genome, with which we are mapping genes responsible for reproductive potential. We are also using these markers to reconstruct the evolutionary history of hybridization in this group of ants, and test competing hypotheses for how caste mechanisms evolve. In addition to mechanistic questions, we have an ongoing interest in understanding the ecological and evolutionary context in which genetic caste determining systems evolve and are maintained.
Acclimation and Adaptation to Climatic Warming in Northeast Temperate Forest Ant Communities
This collaborative project with Dr. Nicholas Gotelli and Bryan Ballif at UVM, along with Aaron Ellison at Harvard Forest, Rob Dunn at North Carolina State University and Nathan Sanders at the University of Tennessee Knoxville, is funded by a Dimensions of Biodiversity grant from the National Science Foundation. We are looking at how ant communities respond to temperature increases such as those projected to occur in the northeast US over the coming 50-100 years. How species deal with climatic change is expected to critically depend on their inherent tolerance to temperature extremes, local genetically-based variation in temperature tolerance traits, and the potential for movement of better adapted alleles from more southern populations northward as habitats shift northward. We are using both targeted-gene approaches and next-generation transcriptome sequencing (RNA-seq) to characterize short and long-term responses to increased temperatures in a common north temperate forest ant ant, Aphaenogaster rudis, and test whether latitudinal range breadth acts as a genetic reservoir for thermal resiliency in the face of climate shifts.