Ecological niche modeling shed light on new insights of the speciation processes and historical distribution of Japanese fire-bellied newt Cynops pyrrhogaster (Amphibia: Urodela)

Environmental factors play vital roles in determining the range of organisms and application of selective pressures that drive their evolution. Investigation of how these ecological factors influence the diversification of species has long been a point of interest among ecologists. In this study, we used climate-based ecological niche models to project the suitable distributions of four main clades of Japanese fire-bellied newt Cynops pyrrhogaster at the Last Glacial Maximum (LGM), Mid-Holocene (MH), and the present. Then we tested hypotheses regarding ecological niche diversification and the processes of diversification among these clades. The potential distribution of the Northern clade encompassed the Tohoku and Kanto districts, along with the northeastern Chubu district. The Central clade had a potential distribution across the Chubu and Kinki districts, and northeastern Chugoku district. The range of the Western clade was projected to encompass Kyushu, Shikoku, the southern Kinki region, and western Chugoku. Finally, the projected distribution of the Southern clade was limited to the southern Kyushu district. The lack of equivalent niches among the tested pairs indicated the absence of ecological interchangeability among the clades. The results of a similarity test supported significant parapatric divergence of the Northern and Central clades from the remaining clades. On the other hand, the Western and Southern clades probably underwent divergence through an allopatric process. Our paleomodels suggest that the distribution of C. pyrrhogaster may have been reduced and fragmented along the coastal regions during the LGM. The distribution models for the MH estimated a suitable area larger than for the LGM, but smaller than predicted by the current distribution. Our findings serve as a warning that the potential distributions of species could be significantly influenced by future climate change.