Population genetic structure of Commerson’s dolphins (Cephalorhyncus commersonii) along the continental patagonian coast based on MtDNA.

COSCARELLA, MARIANO ALBERTO; HOELZEL, RUS A.; CRESPO, ENRIQUE ALBERTO; LOIZAGA DE CASTRO, ROCÍO

San Sebastián, España

Conferencia; 21 ANNUAL CONFERENCE OF THE EUROPEAN CETACEAN SOCIETY; 2007

European Cetacean Society

Commerson’s dolphins are subject to the impact of several human activities along the  Patagonian coast (e.g. incidental mortality and dolphin watching operations). The species is managed independently in each Province applying different criteria, leading to different regulations. Within this framework it is essential to assess the genetic structure of putative populations. Skin samples were collected by means of the skin swabbing technique, preserved in ethanol 96% from 6 localities, covering the full distribution range of the species on the Patagonian coast. A fragment of 775pb of the mtDNA control region was sequenced for 161 samples. Sex was determined by means of molecular techniques and parity among sexes was tested using a C2.  A phylogeny was reconstructed using neighbour-joining and the Kimura 2-parameter model. Population structure was assessed by Fst and Fst for haplotype data and the AMOVA routine implemented in Arlequin v3.1. A population expansion analysis was performed calculating the Tajima’s D and Fu’s Fs statistic, and using the coalescent approach with a mismatch distribution. Sex ratio was different from parity (C2, df=1, p0.001), biased towards females in a proportion 2.05:1. Thirty four polymorphic sites were detected defining 40 haplotypes. The overall nucleotide diversity was estimated at 0.005957 (SE=0.0011429). The nucleotide diversity for every sampling location was in the same order of magnitude as the overall, ranging from 0.004166 to 0.00653. Gene diversity ranged from 0.09388 to 0.5145. The AMOVA indicated that 82% of the molecular variance is found within the putative populations; nevertheless 18% of the remaining variance among populations is highly significant (p<0.001). The mismatch analysis is consistent with the Tajima’s D and Fu’s F statistics (both non significant for every population except one). The combined sample shows no signature of expansion. MtDNA analyses detected six local populations along the Patagonian coast.