Population genetic structure of a California endemic Branchiopod, Branchinecta sandiegonensis

Branchinecta sandiegonensis (Crustacea: Anostraca) is a narrow range endemic fairy shrimp discontinuously distributed in ephemeral pools on coastal mesas in San Diego County, USA. Ten populations across the range of the species were subjected to allozyme analysis for eleven loci. The species exhibits low variability (P₉₅ =9.1–45.5) and one third of the loci tested did not conform to Hardy-Weinberg equilibrium expectations. The species also exhibited a high degree of genetic differentiation between populations. F _ST values (fixation index) for most pairs of populations were above 0.25 (0.036–0.889).Low genetic variability and high genetic structure may result from low gene flow and founder effects due to habitat fragmentation and the lack of potential vectors for cyst dispersal. The unpredictable rainfall of the region also creates potential for variable population sizes which could affect structure and variability.