2021 年 3 巻 p. 152-163
To describe global genetic diversities and genetic structure of sei whales, population genetic and phylogenetic analyses were performed using mitochondrial DNA (mtDNA) control region sequence (480 bp) data from specimens collected in three oceanic regions: North Pacific (NP: n=39), North Atlantic (NA: n=84) and Southern Hemisphere (SH: n=6). Microsatellite DNA (msDNA) analyses were also performed using genotype data at seventeen loci in a sub-set of samples (n=39 in NP and n=4 in SH). The haplotype (h) and nucleotide (π) diversities were higher in NP (h=0.92 and π=0.009) and SH (h=1.00 and π=0.012) than in NA (h=0.68 and π=0.002). The haplotype frequency was significantly different among the three oceanic regions, and the conventional pairwise FST estimates support the difference between NA and the other two populations. Furthermore, except for one haplotype, there were no other shared haplotypes among the three oceanic regions, suggesting contemporary migration and gene flow would be strongly restricted at inter-oceanic scales. This inference was also supported by the msDNA analyses. The haplotype genealogy reconstructed by the maximum-likelihood approach strongly supported two clusters, the first consisting of NA haplotypes, and the second consisting of NP and SH haplotypes. This genealogy was supported by the statistical parsimony haplotype network. These results indicated hierarchical genetic structuring of sei whales globally, in which whales in SH are genetically closer to NP whales than to NA whales. Based on a comparison of the inter-oceanic genetic structure and phylogeny of the sei whales with those of fin whales, which is another cosmopolitan baleen whale species, it is suggested that the genetic structure of sei whales reflects occasional gene flow between the Northern and Southern hemispheres and/or incomplete lineage sorting, similar to the case of fin whales.
