Evolution of Cheaters in an Obligate Mutualism: An Experimental Approach

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0075944PellmyrMutualistic interactions create resources that are exploited by parasites. These parasites sometimes evolve from mutualists and they can greatly alter the dynamics of the interactions. Obligate mutualisms, such as those between seed-parasitic pollinators and their hosts, make excellent models for the study of such reversals because of their simplicity. This study will use a recently evolved cheater yucca moth and its pollinating sister species to test the first explicit scenario for any obligate mutualism of how it can evolve. In this scenario, specific life history traits and ecological context are suggested to greatly facilitate this type of diversification. The project has three objectives. First, the study will use phylogenetic analysis based on mtDNA and morphometric data to test explicit hypotheses about changing geographic ranges and history of coexistence between the cheater, two pollinators, and their shared host over the last 2-3 million years. Second, experiments will be used to test the hypothesis that the pollinator that gave rise to the cheater has requisite behavioral plasticity and ovipositor morphology to make the shift from pollinator to cheater habit comparatively easily. Third, the study will test a hypothesis suggesting that offset emergence phenology between coexisting pollinators facilitates the evolution of cheating in the later species. Taken together, this project would place a multi-species mutualism in its historical biogeographic context, and use a very recent case of evolution of cheating within that mutualism as a template to experimentally test specific but generalizable hypotheses about this ecologically important process of diversification.