BOHONAK, Andrew J.; FLORES, Michael; WILSON, Jennifer; MARTINEZ-VERGARA, Milmer; SIMOVICH, Marie A.; San Diego State University; San Diego State University; San Diego State University; San Diego State University; University of San Diego: Extreme genetic endemism in an endangered fairy shrimp

For many freshwater invertebrates, conventional wisdom regarding connectivity among populations (i.e., dispersal and gene flow) is largely a matter of speculation. We have been studying genetic and ecological connectivity among populations of the fairy shrimp Branchinecta sandiegonensis in San Diego County. B. sandiegonensis is a federally endangered species, with habitat losses thought to exceed 90%. For the mitochondrial gene CO I, 39 unique haplotypes (alleles) have been identified from over 200 individuals in 24 �complexes� of hydrologically linked pools. There is a high degree of endemicity apparent within local pool complexes, with many complexes fixed for unique haplotypes. Regional genetic differentiation is high. These patterns are particularly obvious in peripheral populations, and in areas with little anthropogenic disturbance. Most surprisingly, we have detected two highly divergent genetic lineages within the species. With very few exceptions, pool complexes contain haplotypes from only one lineage. We recommend that anthropogenic homogenization of this species across its range be minimized as much as possible. Evolutionary significant units (ESUs) that should be prioritized for conservation include the two major clades and individual pool complexes. According to some interpretations of the ESU concept, every pool complex could be considered an ESU worthy of separate consideration. We are currently expanding the study to look for concordant patterns in microsatellite markers.