Genetic characterization and population genetic structure of the Antarctic minke whale Balaenoptera bonaerensis in the Indo-Pacific region of the Southern Ocean

The population genetic structure of the Antarctic minke whale in the Antarctic sector corresponding to the Indo-Pacific was investigated using the mitochondrial DNA control region sequence (338 bp) and microsatellite DNA at 12 loci. Whale samples were obtained in JARPAII (Japanese Whale Research Program under Special Permit in the Antarctic-Phase II) surveys performed during the austral summer seasons of 2005/06 to 2010/11. The Indian Sector comprised the area between 35A degrees and 130A degrees E, while the Pacific Sector was between 165A degrees E and 145A degrees W. The mtDNA/nDNA sample sizes in the Indian and Pacific sectors were 1210/1372 and 795/882 animals, respectively. The level of genetic diversity was high for both genomes, and was similar for the two sectors. In both sectors, the mismatch distribution for whales did not suggest a population at equilibrium. Results of a heterogeneity test showed significant genetic differences between whales in the two sectors, suggesting that different populations inhabit the Pacific and Indian sectors of the Antarctic. Microsatellite DNA analyses showed more dispersal in males than females, and also some degree of annual variation. Significant departure from Hardy-Weinberg equilibrium suggested some geographical overlap of the populations in the feeding grounds. The two populations identified in the Antarctic feeding areas of the Indian and Pacific sectors could be related to the suggested breeding areas in the eastern Indian Ocean and western South Pacific, respectively. The segregation of the populations in the Antarctic feeding grounds could be explained by the fidelity of whales to specific areas with krill concentrations.