Introduction
I. Bufo gargarizansspecies complex
The Asiatic toad, Bufo gargarizans , (Cantor, 1842), is distributed in China, Russia, North Korea, South Korea, and Japan (Miyako and Ryukyu Islands). Bufo gargarizans is currently classified as Least Concern in the IUCN Red List because of its large habitat range, but it is likely to be classified as a risk category if a threat occurs (IUCN, 2019). This species has had a complicated taxonomic history (Hu, Jiang & Tian, 1984; Huang, Jin & Cai, 1990; Macey et al., 1998; Liang, Changyuan & Jianping, 2010), with several species being recognized as distinct or the same species as B. gargarizans (Fu et al., 2005). Some molecular studies considered B. andrewsi , B. minshanicus , and B. tibetanus to be synonyms of B. gargarizans , whileB. bankorensis is treated as a distinct species (Chen et al., 2013; Yu, Lin & Weng, 2014; Tong & Wo, 2017; Frost, 2020).
Genetic studies of B. gargarizans have provided insight into its evolutionary history. An allozyme-based study of B. gargarizanscomparing individuals from Korea and China confirmed a clear genetic difference between the two regions (Yang et al., 2000). Zhan and Fu (2011) performed a multilocus molecular study using both mitochondrial DNA (mtDNA) and nuclear DNA (nuDNA), and sampled B. gargarizansthroughout China covering four major geographic regions (West [W], Central [C], Southeast [SE], Northeast [NE]); they recovered seven clades not differentiated based on geography (e.g., Clade A included samples from the W, C, and NE). The most recent study (Borzée et al., 2017) used two mtDNA markers (control region, NADH dehydrogenase 2 [ND2 ]) to study the phylogeography of B. gargarizansin China and South Korea, and found a clade of individuals from South Korea and across China. Zhan and Fu (2011) and Borzée et al. (2017) have contributed to our understanding of the evolutionary history of B. gargarizans , but both had reasonable limitations in their study design. To clarify the genetic status of the B. gargarizans species complex, we combine the strengths of previous studies by including comprehensive geographic sampling and multiple molecular loci.