A preliminary note on population structure in eastern South Pacific common bottlenose dolphins, <i>Tursiops truncatus</i>

Previous studies of eastern South Pacific common bottlenose dolphins, Tursiops truncatus, defined offshore and inshore ecotypes in Peru based on cranial and tooth morphology, documented the presence of a single resident inshore community (‘pod-R’) in central-north Chile, and confirmed the presence of offshore bottlenose dolphins off Chile. Here, mtDNA control region (331bp) was examined to evaluate genetic relationships between four geographic areas: inshore pod-R (n=8), Chilean offshore population (n=8), Peruvian inshore (n=3) and offshore (n=12)ecotypes. This is the first genetic analysis of T. truncatus in this ocean basin. Phylogenetic analysis grouped the three Peruvian specimens morphologically identified as inshore ecotype in an independent cluster, supported by 100% bootstrap value. The net genetic distance between Peruvian inshore and Peruvian offshore ecotypes was estimated at 2.9%, and even higher when compared with Chilean bottlenose dolphins. Morphological and mtDNA evidence combined argues for considering inshore and offshore ecotypes as evolutionary significant units, to be managed accordingly. Despite its inshore behavioural ecology, pod-R presented a high divergence from the Peruvian inshore ecotype and a relatively closer affinity with the Chilean offshore stock (3.41% and 0.87% net interpopulational distance, respectively). However, homogeneity tests showed significant genetic differences of pod-R with all other groups, including Chilean offshore. This, combined with a low nucleotide diversity (0.0069) and behavioural observations, suggest that pod-R may be reproductively isolated and active protection measures are recommended. Only one haplotype from a total of 21 was shared by Peruvian and Chilean offshore animals. Their net genetic distance was estimated at 0.024 and no significant differences were found in haplotype frequencies, suggesting a single, wide-ranging ‘Peru-Chile offshore stock’

Preliminary mitochondrial DNA analysis in eastern South Pacific bottlenose dolphins <i>Tursiops truncatus</i>. Scientific Committee document SC/55/SM22, International Whaling Commission, May-June 2003, Berlin, Germany

Previous studies of eastern South Pacific bottlenose dolphins Tursiops truncatus, defined offshore and inshore ecotypes based on cranial and tooth morphology in Peru, documented the presence of a single resident coastal community (‘pod-R’) in central north Chile and confirmed the presence of offshore bottlenose dolphins off Chile. Morphological and behavioural differences between pod-R and the transient offshore animals suggested a reproductive isolation. To test this hypothesis and determine the pod-R probable origin, 331bp of mtDNA control region were analysed from the pod-R (n=8), Chilean offshore population (n=8), and inshore (n=3) and offshore (n=12) Peruvian ecotypes, as the first genetic analysis in T. truncatus of the eastern South Pacific. Levels of mtDNA diversity and phylogenetic relationships among haplotypes were determined. Three bottlenose dolphin specimens, morphologically identified as Peruvian inshore, grouped in an independent cluster supported by a bootstrap value of 100%. The net genetic distance between Peruvian inshore and Peruvian offshore was estimated at 2.9% and even higher when compared with the Chilean groups. The combination of morphological and mtDNA evidence conclusively argues for a reconsideration of the taxonomic status of the inshore ecotype. Further studies are required to determine boundaries of its distribution range and to estimate its population size and trend. Despite its inshore behavioural ecology, ‘pod-R’, which is the only resident bottlenose dolphin community recorded in Chile, presented a very high divergence from Peruvian inshore form (3.41% net interpopulational distance) and a relatively closer affinity with the Chilean offshore stock (0.87% net interpopulational distance). However, homogeneity tests showed significant genetic differences of pod-R with all other groups, including Chilean offshore. This, combined with a low nucleotide diversity of 0.0069 strongly suggests that ‘pod-R’ may be reproductively isolated and active protection measures and continuous monitoring of its status are recommended. Only one haplotype (from a total of 21) was shared by Peru and Chile offshore animals. The net genetic distance between them was estimated at 0.024% and no significant differences were found in haplotype frequencies, suggesting they form a single, wide-ranging offshore stock of unknown abundance