Eight Novel Microsatellite Loci Clearly Distinguish Two Tursiops truncatus Populations

Marthajane Caldwell
University of Miami, Department of Biology, 1301 Memorial Drive, Coral Gables, FL 33124

In species that are difficult to study, getting accurate information on basic population parameters is challenging. Molecular approaches can help. For example, mtDNA sequence data suggest that there may be both a coastal and offshore species of bottlenose dolphin (Tursiops truncatus) in the northwest Atlantic where only one species is currently recognized.

To examine population structure in coastal dolphins in Florida, I developed eight microsatellite loci from a size selected genomic library in Lambda Zap Express (Stratagene). I used these loci to genotype 12 offshore and 17 coastal Tursiops truncatus. Here I report characteristics of these loci and their application to the coastal/offshore division.

The eight loci averaged nine alleles (range = 5-14). Sixty one percent (n=43) of the 70 alleles were unique to the offshore samples and 24% (n=17) to the coastal samples. In the offshore sample, there were more observed homozygotes than expected at four loci. Only one locus in the coastal sample had more homozygotes than expected. This departure from Hardy-Weinberg suggests a high level of inbreeding. Alternatively, this difference may be due to the fact that the offshore samples were obtained from a mass-stranding event whereas the coastal samples were obtained from individual stranded dolphins. Significant genetic differentiation was found between the offshore and coastal samples at each locus (p < 0.000). The overall Fst, 0.29 (range = 0.04-0.44), is an order of magnitude higher than that found in other species. These data strongly suggest that these populations are genetically distinct.