Contrasting phylogeographic patterns among Northern and Southern Hemisphere fin whale populations revealed by new data from the Southeastern Pacific and Gulf of California
M.J. PÃ©rez-Ãlvarez, S. Kraft, C. OlavarrÃa, J. UrbÃ¡n, S. Nigenda-Morales, L. Viloria, R. Wayne, F. Archer, R. Moraga, M. SepÃºlveda, M. Santos-Carvallo, G. Pavez and E. Poulin
Three sub-species of fin whales are currently considered valid: Balaenoptera physalus physalus in the Northern Hemisphere (NH), and B. p. quoyi and B. p. patachonica in the Southern Hemisphere (SH). The latter was described as a pygmy-type sub-species located in low to mid latitudes in the SH. In the NH, a strong genetic differentiation was previously detected between North Pacific (NP) and North Atlantic (NA) fin whales, which lead to a current debate of a taxonomic division between these two groups. Additionally, a highly isolated population has been detected in the Gulf of California (GoC), Mexico. Little is known, however, for the SH, impeding a global biogeographic and taxonomic revision of the taxon. This study includes sequences previously reported for NA, NP, and South Atlantic (SA), the first samples of the Southeast Pacific (SEP) (n=37 as well as new mtDNA sequences from GoC (n=107) improving the worldwide phylogeographic and demographic picture of the species. SEP sequences recovered 25 haplotypes with nine shared by two or more individuals, a haplotype diversity (h) of 0.979 and nucleotide diversity (Ï€) of 0.8%. In contrast GoC showed only five haplotypes (h = 0.3 and Ï€ = 0.06%). A strong genetic structure was observed as previously between (1) NP and the GoC populations, the latter being a differentiated unit under a recent population expansion process and (2) more robustly between NP and SP populations, where a low and unidirectional and rare dispersal event flow from SP to NP was further confirmed. Contrary to the NH, (3) no significant phylogeographic structure was detected within the SH (SP and Atlantic Southern Ocean; ï†ST = 0.00582, p = 0.235), which suggests the existence of a single evolutionary unit and challenge the validity of the proposed pygmy fin whale sub-species. Finally, (4) B. physalus would include four major population units (three for the NH and one for the SH).