Genetic Characteristics and Population Structure of Humpback Whales in the Antarctic Feeding Ground as Revealed by Mitochondrial Dna Control Region Sequencing and Microsatellite Analyses

Biopsy samples from 411 humpback whales obtained during surveys of the Japanese Whale Research Program under Special Permit in the Antarctic and International Decade for Cetacean Research/Southern Ocean Whale and Ecosystem Research were analyzed in order to describe their genetic population structure in the Antarctic feeding grounds. Samples were obtained from International Whaling Commission (IWC)-designated management Areas III (n= 81), IV (n= 172), V (n= 97) and VI (n= 61), and were examined for i) sex determination, ii) the sequence variation of the first 334bp nucleotides of the mtDNA control region and iii) genetic variation at the genotypes of six microsatellite loci. Duplicated samples were excluded from the analysis. The level of genetic diversity in the Antarctic was high for both genomes: the nucleotide diversity at the mtDNA was estimated at 0.0263 and the mean expected heterozygosity at the nuclear loci at 0.7820 for the total samples. In general results based on both mtDNA and microsatellites were similar and they suggest population structure of humpback whales in the Antarctic feeding grounds. These genetic results are consistent with the previous view based on nongenetic data that Areas III, IV, V and VI are occupied by different populations. The most plausible pattern of structure in the Southern Hemisphere therefore is multiple breeding and feeding grounds with some extent of site fidelity. Marked differences were found between whales in Areas IV and V for both mtDNA and microsatellites, and the same pattern was found for both sexes. Results of the other pair-wise comparisons among Areas showed more subdivisions in females than in males. An explanation for this result is that the difference is due to the lower sample sizes for males in these comparisons. The possibility of intermingle of populations in bordering sectors can not be discarded yet and a comprehensive analysis that involves genetic data from low and high latitude, as recommended by the Scientific Committee, is necessary to solve this issue.