Multi-species interactions and the evolution of biological systems

In this thesis I develop several models examining how genetic evolution can affect evolutionary processes at a broader scale. First, I ask how evolution would proceed at a locus that governs the mutation rate between alleles mediating interactions between hosts and parasites. By relaxing several simplifying assumptions I am able to explore the affects of sex and recombination. I find that, when the modifier locus is completely linked, the mutation rate evolves toward the optimum rate. With looser linkage, however, lower mutation rates evolved. This work can potentially explain the high rates of antigenic switching observed in many asexual taxa. Second, I investigate how ploidy levels and the genetic model underlying species interactions affect how evolution proceeds from a free-living to a parasitic life-history. I find that the transition to parasitism occurs over a broader range of parameters when the parasite is haploid. The role of host ploidy is more complicated, depending on the model governing host-parasite interactions. These results provide a first characterization of how genetic architecture affects selection on life-history in antagonistic species interactions. Third, I develop a model of sexual selection in an environment with spatial variation in the carrying capacity, but no variation in resource type. I show that, when searching for a mate is costly, this variation can stabilize demographic fluctuations, facilitating long-term coexistence of species differing only in sexual traits. This is the first study to demonstrate the existence of conditions under which sexual selection alone can promote the long-term coexistence of ecologically equivalent species in sympatry. Finally, I develop a model characterizing the effects of mating preferences on species interactions in hybrid zones. I find that the spatial distribution of genotypes observed in many "mosaic" hybrid zones might be better explained by species-specific differences in mating than by differences in ecology (the common explanation). In addition, I develop a statistical method that can be applied to empirical hybrid zone data to estimate how "mosaic" the hybrid zone is. I test this statistic on data from the Mytilus edulis and M. galloprovincialis hybrid zone.Science, Faculty ofZoology, Department ofGraduat