Recent Distributional Shifts and Hybridization in Marine Fishes of Japan

Abstract

The Japanese Archipelago separates the Sea of Japan from the North Pacific Ocean to the west and east, respectively. The Sea of Japan is a semi-enclosed marginal sea, on which the influence of global warming was remarkable during the twentieth century. The sea surface temperature rose three times faster than that of the world ocean, including the North Pacific Ocean. In response to the warming of the Sea of Japan, rapid northward range shifts have been observed in many marine fishes, some of which have shown increases in the rate of natural hybridization with their close relatives. A notable example is the mass occurrence of natural hybridization observed between two closely related pufferfishes, Takifugu snyderi and Takifugu stictonotus, between 2012 and 2014. Another example is the recent increase in the number of natural hybrids between two yellowtails, Seriola quinqueradiata and Seriola lalandi. In both cases, rapid distributional shifts in one of the two species, and the rarity of one parental species in spawning populations, were the likely causes of the increased hybridization. In the former example, past mitochondrial DNA introgression was distinguished from the recent and ongoing hybridization, indicating that hybridization has occurred not only recently, but also occasionally in the past. Although there is evidence of ancient hybridization in many other marine fishes, where past hybridization may have played a role in their diversification, the effects of environmental changes on the temporal dynamics of hybridization remain largely unknown. Continuous monitoring and the application of population genomics to these ongoing hybridizations may provide insight into the relationship between climate change and hybridization dynamics, where the global temperature is now approaching that of the last interglacial period.