Genetic differentiation and intraspecific structure of Eastern Tropical Pacific spotted dolphins, Stenella attenuata, revealed by DNA analyses

Mitochondrial DNA (mtDNA) control region sequences and microsatellite loci length polymorphisms were used to investigate genetic differentiation in spotted dolphins (Stenella attenuata) in the Eastern Tropical Pacific and to examine the intraspecific structure of the coastal subspecies (Stenella attenuata graffmani). One-hundred and thirty-five animals from several coastal areas and 90 offshore animals were sequenced for 455 bp of the mitochondrial control region, resulting in 112 mtDNA haplotypes. Phylogenetic analyses and the existence of shared haplotypes between the two subspecies suggest recent and/or current gene flow. Analyses using chi(2), F-ST (based on haplotype frequencies) and Phi(ST) values (based on frequencies and genetic distances between haplotypes) yielded statistically significant separation (randomized permutation values P < 0.05) among four different coastal populations and between all but one of these and the offshore subspecies (overall F-ST=0.0691). Ninety-one coastal animals from these four geographic populations and 50 offshore animals were genotyped for seven nuclear microsatellite loci. Analysis using F-ST values (based on allelic frequencies) yielded statistically significant separation between most coastal populations and offshore animals, although no coastal populations were distinguished. These results argue for the existence of some genetic isolation between offshore and inshore populations and among some inshore populations, suggesting that these should be treated as separate units for management purposes.