Population genetic diversity and historical dynamics of Fraser's dolphins Lagenodelphis hosei

Marine organisms face relatively few barriers to gene flow, and yet even highly mobile species such as dolphins often show population structure over regional geographic scales. Understanding the processes that promote this pattern of differentiation helps us understand the evolutionary radiation of this group, and to promote more effective measures for conservation. Here we report the first population genetic study of Fraser's dolphin Lagenodelphis hosei (Fraser, 1956), a species that was not recognized by the scientific communities until the early 1970s. We use 18 microsatellite DNA loci and 1 mitochondrial DNA (mtDNA) locus to compare 112 Fraser's dolphins collected in various locations, mainly from the waters off Japan, Taiwan, and the Philippines, but also including samples from the Gulf of Mexico and Caribbean Sea. Our results indicate differentiation between populations in waters off Japan, Taiwan, and the Philippines, and support the findings from earlier morphological assessments for differentiation between Japanese and Philippine waters. Small sample sets also show likely differentiation between other regions in the North Pacific and North Atlantic Oceans. Moreover, neutrality tests and mismatch analysis based on mtDNA data indicate that the populations in the western North Pacific Ocean have expanded demographically and spatially, possibly since the latest global deglaciation, when sea levels and global temperatures started to rise.