UC Merced

Patterns of dispersal and gene-flow in freshwater invertebrates have often been difficult to interpret. Despite the assumed high potential for dispersal, populations of freshwater invertebrates display high genetic differentiation over small distances. There have been several explanations posed for this gene flow dispersal paradox, including strong priority effects or low realized dispersal. This study explores the spatial genetic structure of the freshwater invertebrate Branchinecta lynchi, a threatened vernal pool inhabitant, at two scales with a goal to determine the scale at which gene flow is important in shaping these patterns. Vernal pools were sampled at two different localities the San Luis National Wildlife Refuge Complex and a preserve adjacent to the University of California, Merced. Individuals were genotyped using both the mitochondrial cytochrome oxidase I subunit (COI) and nuclear amplified fragment length polymorphisms (AFLPs). Pairwise Fst values showed that genetic structure for this species was high, however, the only geographic pattern that emerged was isolation by distance at the local scale for the COI marker. Discrepancies between mitochondrial and AFLP markers may be explained several ways, including genotyping error, sex-biased dispersal and/or the longer time to equilibrium of the nuclear genome. These results suggest that gene flow is important at the local scale, at least for mitochondrial DNA, while historical colonization patterns are likely maintained at the regional scale by priority effects. I infer that maintaining connectivity among vernal pool complexes through local dispersal vectors should be a management priority.