Through the looking glass: host-parasite coevolution and sex
Abstract: Why cross-fertilize? “Reproduction” is an obvious answer, but many species reproduce asexually via the production of viable, unfertilized eggs. Reproduction, therefore, does not require sex. A more likely explanation is that cross-fertilization results in the production of genetically variable offspring. But why is variation beneficial? What problem does variation solve?
In this talk, I will synthesize four decades of our work on this question. The work has been mostly focused on a freshwater snail in which sexual and asexual females coexist. Most of the work was designed to test the idea that host-parasite coevolution can favor cross-fertilization in hosts (and parasites). The gist of the idea is that parasites rapidly evolve to infect the most common host genotypes. Hence, clonal reproduction might be favored when the clone is rare. But once the clone becomes common, parasites/pathogens should rapidly evolve to infect it. Such infection might then reduce the frequency of the clone in the population. Cross-fertilization, on the other hand, might avoid the boom-and-bust cycles of obligate clonal reproduction. Experimental and observational studies of the snail system support this view.
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