The water toad (Bufo stejnegeri) is endemic to Northeastern Asia (South Korea, North Korea, and China) and has unique ecology for a toad by being semi-aquatic and breeding in lotic environments. We use a suite of phylogenetic analyses to understand the evolution of B. stejnegeri's distinctive ecology and the impact of Pleistocene glacial cycles on the biodiversity of Northeast Asia. For the evolution of a semi-aquatic lifestyle, although B. stejnegeri is relatively closely related to two other semi-aquatic Bufo species (B. torrenticola and B. andrewsi), ancestral state reconstruction analysis infers an independent evolution in all three species. Upon closer inspection, B. stejnegeri exhibits major differences in amplexus and egg-laying behavior compared to the other two species, supporting independent evolution. Divergence dating analyses infer B. stejnegeri to have originated during the Late Miocene-Early Pliocene (4.3 Ma, 2.7–6.2 Ma). This species does not exhibit population differentiation with respect to mountain range, but shows a preliminary genetic pattern of southern richness and northern purity supporting a single refugium in Korea during Pleistocene glacial cycles. The Bayesian skyline plot supports this inference, suggesting a population decline followed by expansion during the Pleistocene. Although not as species rich as the tropics, we hope this study helps spark interest in Northeast Asian biodiversity.
Bibliographical noteData Availability Statement
The datasets generated for this study can be found in GenBank with the following accession numbers: MK031411–MK031654.
The animal study was reviewed and approved by Seoul National University Ethics Committee.
JF, B-TY, P-PL, BW, and M-SM designed the study and wrote the manuscript. JF, B-TY, and M-SM collected samples. JF and B-TY analyzed the data.
This research was supported by grants from the National Research Foundation of Korea (2012K1A2B1A03000496) funded by the Government of the Republic of Korea (MSIP), and the Research Institute of Basic Sciences, Seoul National University (to BW), and from the National Natural Science Foundation of China (31211140342) (to P-PL). We thank Profs. Wenbo Liao and Jinzhong Fu for information on the reproductive biology of B. andrewsi. We would like to thank members of the Min and Waldman labs for help with fieldwork, and thank Adam Leache for help with divergence dating analyses.
- ancestral state reconstruction
- Baekdudaegan Mountain Range
- Bayesian skyline
- divergence dating
- Northeast Asia