Meeting Abstract
Understanding the evolutionary processes that cause populations to diverge genetically and phenotypically is crucial to predicting how species will respond to rapid global environmental change. The Olympia oyster, Ostrea lurida, is patchily distributed from California to the central coast of Canada, extending over strong environmental clines and mosaics that are typically considered necessary for local adaptation to occur. Before testing hypotheses of adaptation, however, the underlying demographic population structure must be described. This pattern could be consistent with a null model of no significant population structure, a continuous isolation-by-distance (IBD) model, or contain regional blocks of genetic similarity separated by barriers to gene flow. We hypothesized that, by using thousands of genetic markers, evidence of regional population structure and IBD will be observed across the species’ range. Adult Olympia oysters were sampled across 20 sites from Klaskino Inlet, Vancouver Island (50° 17’ 55”) to San Diego Bay, CA (32° 361’ 9”), as well as 15 individuals from the sister species, O. conchaphila. DNA from these samples were used to construct reduced representation Genotype-by-Sequencing libraries (GBS) and genotype thousands of single nucleotide polymorphisms (SNPs). A Mantel test using Fst and water distance rejected the hypothesis of pure isolation by distance. Using a new method to visualize spatial population structure called EEMS (Estimated Effective Migration Surfaces), we have identified a phylogeographic divide between Puget Sound, WA and Willapa Bay, WA. Although this method cannot distinguish between different scenarios that could produce the observed spatial structure, it supports the rejection of both a continuous IBD model and the null model of no significant genetic structure.
