Genetic diversity of South East Pacific fin whales and lack of genetic differentiation between Southern Hemisphere stocks
Maria Jose Perez-Alvarez, Carlos Olavarria, Sebastian Kraft, Rodrigo Moraga, Maritza Sepulveda, Macarena Santos-Carvallo, Guido Pavez and Elie Poulin
International Whaling Commission
The fin whale is distributed from temperate to subpolar waters of both hemispheres. Currently, three sub-species of fin whales are considered valid, Balaenoptera physalus physalus in the Northern Hemisphere (NH), B. physalus quoyi and B. physalus patachonica in the Southern Hemisphere (SH). The latter is described as a pygmy-type sub-species and proposed to be located mainly in low to mid latitudes in SH (Clarke 2004). Recently, Archer et al. (2013) detected a strong genetic differentiation between North Pacific and North Atlantic fin whales, suggesting a taxonomic subdivision at the sub-species level. Little information was available, however, for the South Pacific and South Atlantic oceans, impeding a global taxonomic revision of this taxon. This study aims to contribute to this question with genetic data from the South East Pacific, specifically from a feeding area in the north-central coast of Chile (ca. 29°02'S, 71°36'W). Mitochondrial DNA analysis (Dloop) of 19 biopsy samples recovered 17 different haplotypes, with only two shared between individuals. A haplotype diversity (h) of 0.97 and nucleotide diversity (π) of 0.8% were estimated at a local level. At a global scale, phylogeographic analyses, including different ocean populations (sensu Archer et al. 2013), showed a clear genetic differentiation between Southern and Northern Hemispheres as it has been previously reported, as well as between North Pacific and North Atlantic Oceans. However, we detected a low and unidirectional genetic connection from South to North Pacific. In contrast, no significant genetic structure was detected when comparing populations from the Southern Hemisphere (South East Pacific with that from the Atlantic Southern Ocean; ST = 0.01539, p = 0.1333), even considering samples that would represent the putative pygmy fin whale sub-species (B. physalus patachonica), suggesting the existence of a single evolutionary unit in this area. Therefore, these results might challenge the validity of the proposed pygmy fin whale sub-species and propose the existence of three taxonomic units (two for the Northern Hemisphere and one for the Southern Hemisphere).