KURPIUS, J.W.: Panmixia or genetic differentiation? : Phylogeographic patterns of a planktonic dispersing gastropod in the Eastern Pacific.

Most phylogeographic studies focus on organisms that are predicted a priori to have genetic structure. However, there are relatively few studies that test whether species predicted to be panmictic actually are. Using a population genetic approach, this study tests for significant genetic structure in Littorina keenae, a planktonic dispersing marine taxon that shows little morphological variation and according to traditional life history theory would be predicted to be panmictic. L. keenae ranges from central Oregon to Baja California Sur, an area that spans the traditionally recognized marine biogeographic boundary at Point Conception. This region along the California coast marks a potential physical barrier to gene flow because marine larvae may be transported offshore by strong currents. This study tests whether the biogeographic boundary at Point Conception is a physical barrier to gene flow for this intertidal species. Partial sequences of the mtDNA gene cytochrome c oxidase subunit I (COI) were used in maximum parsimony, statistical parsimony, and molecular-variance parsimony analyses. Results suggest that L. keenae is panmictic and that Point Conception does not represent a barrier to gene flow. The results are concordant with other marine taxa whose ranges span Point Conception and have the capacity for high dispersal. Biogeographic implications of these data will be discussed.