The relationship between gene flow and dispersal for passively dispersed aquatic invertebrates is complex and often difficult to directly estimate. Additionally, local adaptation and competition can greatly influence metrics of gene flow and dispersal for these organisms. We have initiated studies to determine the relative roles of neutral versus adaptive processes in limiting gene flow for large branchiopods that inhabit temporary aquatic habitats (vernal pools) in western North America. Our study area contains highly diverse soil substrates, which we can use to test hypotheses concerning the role of local adaptation in limiting gene flow, and possibly dispersal, for a diverse array of vernal pool crustaceans. To assess genetic connectivity among populations of the fairy shrimp (Branchinecta lynchi) we have typed individuals at both mitochondrial and nuclear markers.
Results/Conclusions
The genetic data indicate that gene flow and within population variation varies across our study site as a function of soil age, and not geographic distance. Older soil surfaces contain isolated populations where genetic drift is the overriding mechanism influencing within and among population variation. Recurrent colonization and higher gene flow is more common in populations that inhabit younger soil surfaces. This suggests that local adaptation to soil surface properties (which drive the aquatic conditions of vernal pools) limit gene flow in our study system. These results have implications not only for determining within species dynamics, but also are important for community level processes and establishing conservation priorities for sensitive vernal pool crustaceans.