INSECT BEHAVIOR & EVOLUTION
Given their cosmopolitan distribution, seed beetles also provide a good system for studying population differentiation. We have been especially interested in the evolution of larval competitive behavior, which can be strikingly different between interfertile populations. Female oviposition behavior also varies widely, including the tendency of egg-laying females to avoid occupied seeds (and thus minimize the degree of competition experienced by their offspring). Seed beetles also provide a good system for investigating the magnitude of inbreeding depression in insect populations. Few studies have examined the effects of inbreeding on insect behavior outside the context of mating success. We investigated the effect of moderate inbreeding on female oviposition choices, along with other fitness-related traits (body mass, fecundity, and egg hatch) in the same population. Finally, we have examined the mating compatibility of divergent beetle populations in order to detect incipient stages of pre- or post-copulatory isolating mechanisms.
A current project examines beetle adaptation to an extremely poor host - lentil. Initial assays indicated that larval survival in lentil was about 1%, and a substantial number of females did not recognize lentil as an oviposition host. Nevertheless, three independent bouts of mass selection produced lines with >60% larval survival within only 5-8 generations, and >90% survival in 25-30 generations. We performed crosses between lentil lines (>90% survival) and a line maintained on the ancestral host. Analyses of F1, F2, and backcross hybrids indicated both additive and non-additive genetic components to the ability to survive in lentil. In addition, both artificial and quasi-natural selection produced significant increases in the tendency to oviposit on lentil. We are using a variety of approaches to understand the specific changes in larval physiology and adult behavior that mediated this radical host shift. We are currently using genome-wide scans to identify potential trade-offs associated with colonizing lentil, as well as investigating whether adapting to such a marginal host causes cross-adaptation to other marginal hosts that are related to lentil.
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