FROST, A.; RIPLEY, B.; VALERO, S.; SIMOVICH, M.; Univ. of San Diego; Univ. of San Diego; San Diego State University; Univ. of San Diego: Apparent Disequilibrium and Reproductive Isolation in an Endangered Fairy Shrimp

Endemic to Southern California, the San Diego fairy shrimp, Branchinecta sandiegonensis, has suffered tremendous habitat loss due to urban development and consequently is on the Federal endangered species list. Information on the genetic population structure of the species is needed for restoration and management decisions. Using mitochondrial DNA and microsatellite DNA, Bohonak has shown that the remaining populations are apparently out of Hardy-Weinberg equilibrium and are composed of two distinct clades (A and B). These results raise two questions: 1) is the apparent disequilibrium an artifact of null alleles? and 2) are the two clades reproductively isolated? We raised shrimp from one pool from each clade and mated pairs within and between clades (AxA, BxB, and AxB). Cysts and parents were genotyped using microsattelites to determine if null alleles were present. Furthermore, the number of cysts produced (female fertility) and the number containing embryos (early viability) from each cross were measured and compared. Crosses within a clade averaged 170.2 cysts and were significantly higher than AxB crosses, which averaged 43.8 cysts. Preliminary results show crosses within clades have greater than 80% viability. Other results are forthcoming.