Graduate Thesis Or Dissertation
 

Population genetics, ecology and evolution of a vertebrate metacommunity

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/wh246w02n

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  • Population genetic structure is widespread in many organisms and can be found at small spatial scales. Fine-scale differentiation is the result of ecological and evolutionary processes working together to produce an overall pattern, but the relative importance of these factors in population differentiation is poorly understood. The goals of my research were to describe patterns of population genetic differentiation and to identify ecological and evolutionary factors important for population divergence. To this end, I investigated several aspects of genetic differentiation for three vertebrates in northern California. The focal species were the terrestrial garter snake (Thamnophis elegans) and the common garter snake (Thamnophis sirtalis) that occupy a series of ponds, lakes and flooded meadows in northern California. I found significant genetic differentiation and isolation by distance, as well as correlated patterns of pairwise divergence in both species. Independent estimates of effective population size and bi-directional migration rates also uncovered source-sink dynamics in both species that suggest frequent extinction-recolonization events within a metapopulation context. The generality of source-sink dynamics for an ecologically similar species within the same ecosystem was explored using a third species, B. boreas. I also identified ecological correlates of several population genetic parameters for all three species. Although F[subscript ST] were similar, B. boreas had larger effective population sizes, lower migration rates, lacked source-sink dynamics, and appeared to be in migration-drift equilibrium, indicative of a temporally stable population structure. A clustering analysis identified a series of block faults as a common barrier to dispersal for both garter snakes, and ecological correlates were found to be more similar among response variables than within species. I then compared degree of genetic differentiation at quantitative traits with that at neutral markers to infer strength of selection and adaptive divergence between two ecotypes of T. elegans. Selection on most traits was relatively weak, but strong diversifying selection was found for background coloration, total number of ventral scales and number of infralabials. Overall, my research documented ecological and evolutionary processes associated with population differentiation in a metacommunity and respresents an important contribution toward the unification of ecology and evolutionary biology.
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