AUTHOR=Fong Jonathan J. , Yang Bao-Tian , Li Pi-Peng , Waldman Bruce , Min Mi-Sook 

TITLE=Phylogenetic Systematics of the Water Toad (Bufo stejnegeri) Elucidates the Evolution of Semi-aquatic Toad Ecology and Pleistocene Glacial Refugia

JOURNAL=Frontiers in Ecology and Evolution

VOLUME=7

YEAR=2020

URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2019.00523

DOI=10.3389/fevo.2019.00523

ISSN=2296-701X

ABSTRACT=<p>The water toad (<italic>Bufo stejnegeri</italic>) 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 <italic>B. stejnegeri</italic>'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 <italic>B. stejnegeri</italic> is relatively closely related to two other semi-aquatic <italic>Bufo</italic> species (<italic>B. torrenticola</italic> and <italic>B. andrewsi</italic>), ancestral state reconstruction analysis infers an independent evolution in all three species. Upon closer inspection, <italic>B. stejnegeri</italic> exhibits major differences in amplexus and egg-laying behavior compared to the other two species, supporting independent evolution. Divergence dating analyses infer <italic>B. stejnegeri</italic> 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.</p>