Mitochondrial DNA variation and population structure of Commerson’s dolphins (Cephalorhynchus commersonii) in their southernmost distribution

Abstract

The Commerson's dolphin, Cephalorhynchus commersonii, is found in shallow waters of the continental shelf off the eastern coast of South America between 40°S and 56°S. This species is taken incidentally in artisanal gillnet fisheries, especially along the shallow coastline of northern Tierra del Fuego and southern Patagonia. The biological importance of by-catch is likely to be underestimated if the boundaries of subpopulations are not properly defined. Here, we report on the sequence variation of the mitochondrial DNA control region of the Commerson's dolphin from five areas defined in Tierra del Fuego, Argentina and Chile, to provide a preliminary assessment of population structure where conservation efforts are most needed. A 466 bp fragment of the mitochondrial DNA control region was sequenced from 196 samples of skin, teeth and bone, defining 20 haplotypes from 17 polymorphic sites. Nucleotide (p = 0.40%) and haplotype (h = 0.807) diversity were low compared to some other odontocete populations, but similar to that of other species of this genus. Genetic differentiation evaluated through analyses of molecular variance (AMOVA) showed significant overall differences among areas within Tierra del Fuego (U ST = 0.059, P \ 0.01). An analysis of sex-specific population structure suggested that the dispersal rates of both females and males are low, indicative of females displaying greater site fidelity. The results from mtDNA control region sequences alone revealed significant differentiation among studied areas, which should be considered as independent management units. We recommend that the impact of localized gillnet mortalities should be managed on a local scale in these areas of Tierra del Fuego.

Population structure and individual movement of southern right whales around New Zealand and Australia

“…dispersal, a common life history pattern seen in mammals (Greenwood 1980), including other ceta ceans (Baker et al 1998, Pimper et al 2010. Although our tests of sex-biased dispersal were not significant, this does not rule out sex-biased gene flow at some point during seasonal migration.…”

First mitochondrial DNA analysis of the spectacled porpoise (Phocoena dioptrica) from Tierra del Fuego, Argentina

“…The analysis of the processes involved in the population structure of cetaceans is difficult to attain due to their high mobility and the few physical barriers of the environment in which they live. Studies of intraspecific variation using molecular markers such as mitochondrial DNA (mtDNA) have been useful in the analysis of the population structure of these species (Pichler et al 1998;Rosel and Rojas-Bracho 1999;Avise 2004;Pimper et al 2010;Taguchi et al 2010;Jayasankar et al 2011).…”

“…Total DNA was isolated from dry skin samples following Pimper et al (2010), and from small fragments of bone and teeth following Pimper et al (2009). The first 380 base pairs of the mtDNA control region were amplified using primers L15824 and H16265 (Rosel et al 1999b) with temperature profiles following Taguchi et al (2010).…”

Mineral and essential element measurements in dolphin bones using two analytical approaches

“…[9] Knowledge concerning feeding habits and genetic diversity using teeth and bone of specimens were performed with this biological material. [10][11][12] Nevertheless, there are other important data regarding the chemical composition of hard tissue that is still limited for marine mammals. [13][14][15][16][17][18][19] Bones potentially provide powerful tools to monitor long-term pollution, but only if consistency of preparation is ensured.…”