II. Phylogeography of Northeast Asia
Northeast Asia (Korean Peninsula, China, and Russia) has had a complex
geological and climatic history, which affected the evolution and
dispersal of organisms in the region. During the Pleistocene,
major geological events (e.g., the
opening of the Yellow Sea, forming of major mountain ranges) and
dramatic climate change are believed to have affected the distribution
of terrestrial vertebrates (Lee et al., 2008; Zhang et al., 2008; Sakka
et al., 2010; Zhang et al., 2012; Kim et al., 2013; Koh et al., 2013;
Fong et al., 2016; Borzée et al., 2017; Fong et al., 2020). In
particular, studies confirmed that the Korean Peninsula was not covered
by glaciers during the latest glacial cycle (Kong, 2000; Yi & Kim,
2010), and this region played an
important role as a refugium in preserving genetic diversity (Lee et
al., 2008; Zhang et al., 2008; Kim et al., 2013; Fong et al., 2020).
Studies on extant amphibians in
this region have clarified the phylogeography of the Chinese
black-spotted frog (Pelophylax nigromaculatus ) (Zhang et al.,
2008), Oriental fire-bellied toad (Bombina orientalis ) (Fong et
al., 2016), Japanese tree frog (Dryophytes japonica group)
(Dufresnes et al., 2016), brown frog (Rana dybowskii ) (Yang et
al., 2017), water toad (B. stejnegeri ) (Fong et al., 2020), and
Asiatic toad (B. gargarizans ) (Zhan & Fu, 2011; Borzée et al.,
2017). Each study had species-specific goals, but a common finding was
that there is genetic divergence between China and Korea likely due to
geology (mountain and oceanic barriers) and Pleistocene glacial cycles.
For B. gargarizans , Zhan and Fu (2011) inferred western China to
be a major refugium for B. gargarizans owing to high genetic
diversity in the region, while Borzée et al. (2017) inferred that this
species dispersed westward from the Korean Peninsula across land bridges
during low sea levels. We provide more clarity on the evolution and
dispersal process of B. gargarizans in Northeast Asia.