Abstract

We investigated the mitochondrial DNA (mtDNA) diversity of humpback whales, Megaptera novaeangliae, wintering off the Mexican Pacific coast and the Revillagigedo Islands. We amplified and sequenced a variable fragment of the mtDNA control region from skin samples of 65 whales and compared these with published sequences from whales in other regional habitats. Among the Mexican humpback whales, we distinguished eight haplotypes differing by 0.31-3.75% along a consensus sequence length of 320 base pairs. A diagnostic restriction site outside the consensus sequence identified a ninth common haplotype. A phylogenetic reconstruction of the control region sequences revealed two main groupings: an AE group, which is common throughout the North Pacific, and a CF group, which is closely related to haplotypes from the southern hemisphere. We found a significant degree of geographic subdivision in the wintering grounds of the eastern North Pacific. Within Mexico, whales off the Revillagigedo Islands are weakly but significantly differentiated from those of the Mexican Pacific coast. Our data also suggest that mtDNA haplotypes are clinally distributed along the American Pacific coast and we hypothesize that the present distribution of these lineages among humpback whales in the eastern North Pacific is probably associated with weather changes after the last glaciation.