GREGG, C.S.; FOLTZ, D.W.; Louisiana State University; Louisiana State University: Genetic variation in bivalve populations from oil-exploration platforms in the Gulf of Mexico

Oil platforms in the northern Gulf of Mexico (GOM) occupy a range of depths from inshore (0 � 30 m) to offshore (30 � 60 m) to bluewater (60 m +), which have different faunal assemblages. Several factors may cause these differences, including dispersal barriers (e.g., hydrographic features, physiological tolerance, predation, competition) and vicariance, which can result in failure to successfully colonize different areas. The present study examined genetic variability in the bivalve Barbatia candida, which lives attached to oil platforms in the GOM. A total of five platforms were sampled along a depth gradient running from inshore at a depth of 15 m to offshore at a depth of 61 m. We examined variability in the mitochondrial cytochrome c oxidase subunit I gene (COX I) among all five populations using direct sequencing and restriction fragment length polymorphism (RFLP) analysis. The sequence data (569 bp of the COX I gene) revealed low divergence among individuals with a maximum p-distance of 1.7% and an overall mean p-distance of 0.6%. No significant population structure was detected among platforms (F_ST = -0.014; p = 0.71) using the RFLP data; however, two out of the four observed RFLP haplotypes were detected only in populations from platforms at >31 m depth. These data indicate that gene flow is occurring among the five populations surveyed, but the greater genetic diversity at inshore populations suggests that there may be asymmetric gene flow among these populations. To determine if there is concordance in this pattern among independent datasets, variability at nuclear loci (RAPDs) in B. candida populations and COX I variation from two co-occurring lithophagid species, Lithophaga bisulcata and L. aristata will also be discussed.