Population genetics of the blue crab in the Gulf of Mexico

Gene flow among blue crabs, Callinectes sapidus , from eleven locations in the Gulf of Mexico (GOM) was estimated using traditional population genetic analyses. Recurrent and historic gene flow were discriminated using nested cladistic analysis to identify ancestral and descendent haplotype lineages and their geographic distributions. Based on comparisons of the complete gene among nine C. sapidus individuals throughout the U.S. range, a 622 base pair region of the mitochondrial cytochrome c oxidase subunit I gene was identified as sufficiently variable for population level analyses following characterization of the variability in the entire 1,534 nucleotide sequence. A total of 213 sequences included 146 haplotypes comprising four distinct lineages. Analysis of molecular variance and phylogenetic analyses indicated restricted gene flow among locations in the western GOM, whereas eastern GOM locations showed no significant population structuring. While most variation was due to variation within the total population, low but significant variation among locations (9.170%) was detected (Φ ST = 0.092, p < 0.0001). Nested cladistic analysis identified a contiguous range expansion in GOM blue crabs which likely coincided with increases in estuarine habitats following late Pleistocene sea level rise. Contemporary gene flow was high. However, dispersal is accomplished primarily by a stepping stone effect rather than consistently long distance dispersal, resulting in isolation by distance between the east and west GOM as well as among several western GOM locations.