Macrogeographic Genetic Structure in Acanthephyra curtirostris (Oplophoridae)

The vast oceanic living space on our planet is occupied by zooplankton species long assumed to be widespread and genetically undifferentiated across their species range. Recently, however, data from sensitive DNA-based molecular markers has shown that many cryptic species exist in the sea and that marine zooplankton species may be more genetically structured than previously thought. In the oceanic environment, the deep-sea appears to be particularly homogeneous with few observable barriers to gene flow and it is also less studied. DNA-based investigations of genetic diversity in the deep-sea are needed to help determine the spatial scale over which species and populations of zooplankton exist in that environment and consequently to inform our understanding of oceanic biology. In this study, gene sequencing and microsatellite analysis were used to test the hypothesis that populations of the deep-sea, cosmopolitan, zooplanktic shrimp Acanthephyra curtirostris (Caridea: Oplophoridae) show genetic diversity within the northeastern Pacific. Tissue samples were collected from two populations off California and one population off Hawaii. Sequence analysis of individuals sequenced for a 635 bp of the mitochondrial COi gene, and a population survey using two microsatellite markers developed for this study, detected substantial genetic diversity among the sampled locations. Unique mitochondrial haplotypes were detected in the Hawaiian population and sequence divergence between the Californian and Hawaiian samples was 3.8%. Microsatellite analysis also revealed genetic variation. Pairwise FST/RST values between all three of the populations were significant showing the presence of moderate population genetic structure even over relatively small oceanic scales. The lack of genetic homogeneity among geographic populations of A. curtirostris provides further evidence that genetic cosmopolitanism is not a valid concept for many species of marine zooplankton and cannot be assumed - even in the deep sea. Microsatellite sequence obtained from A. curtirostris revealed additional information about the nature of microsatellite arrays in decapod crustaceans. The microsatellite repeats isolated from A. curtirostris - the first reported from a caridean shrimp - were found, like those in other decapods, to be abundant, generally long, and extraordinarily complex when compared to other microsatellites reported in the literature