Type: report

Article abstract: A genetic study based on mtDNA sequencing of B. sandiegonensis from across its range found two evolutionary significant units "ESUs" that should be strongly considered for unique conservation status. Pool complexes that are in undisturbed areas are often genetically unique. This project examined population genetic structure in the federally endangered fairy shrimp Branchinecta sandiegonensis in order to gain insight into contemporary and historical connectivity among pools and pool complexes, and make conservation recommendations. Prior to this study, only allozymes had been used to study genetic structure in this species (Davies et al. 1997), and there are very few DNA-level population genetic studies for any fairy shrimp. Davies et al. (1997) found significant genetic differentiation among 10 pools for B. sandiegonensis using allozymes, and evidence for a ?temporal Wahlund effect? within pools. (The importance of overlapping generations created by the fairy shrimp cyst bank may be reflected in heterozygote deficiencies within each pond.) The goal of this study was to expand coverage to include the majority of the species range, including all pool complexes on City of San Diego property. The choice of mitochondrial DNA sequence variation over allozymes for this study reflects the higher degree of precision that can be obtained with mtDNA sequencing. Also, sequence-level variation permits a wider range of analyses that can be used to separate contemporary and historical processes such as allopatric isolation and gene flow.