4.2. Distribution of S. triangularis and S. collaris in China
Sibynophis triangularis was originally described based on a single specimen from Thailand (Taylor & Elbel, 1958). Although initially considered a subspecies of S. collaris , it was subsequently elevated to a separate species, i.e., S. triangularis (Taylor, 1965). At present, this species is known to occur in Thailand and Cambodia (Stuart, Sok, & Neang, 2006; Uetz et al., 2022; Wallach et al., 2014). However, our molecular phylogenetic reconstruction revealed that a particular sample (FMNH 263023, Cambodia), previously identified as S. triangularis (Stuart et al., 2006), formed a well-supported clade (C) with specimens from Vietnam, Myanmar, and China (southern and northwestern Yunnan). Hence, we confirm that clade C represents the species S. triangularis , which is newly reported in China and Myanmar. Currently, S. triangularis is only known to occur in Fugong and Cangyuan in Yunnan of China.
Our results identified clade B as sister to clade C, representingS. collaris based on geographical origin. Unexpectedly, sample CAS 240150 collected from Myanmar and originally identified as S. collaris in Chen et al. (2013) formed a distinct mtDNA lineage from clade B, with genetic distances of 8.3% (cyt.b -based) and 7.9% (ND2-based), respectively (Table 2; Fig. 2). These findings suggest that this specimen was misidentified and may represent an undescribed taxon. Thus, further examination of this specimen is required. In addition, in a previous large-scale systematic study of Chinese snakes, Li et al. (2020) identified one specimen (CHS 244) from Honghe, southern Yunnan, China, as S. collaris , and two specimens (CHS 879 and CHS 880) from Motuo, Xizang, China, as S. chinensis . Our results showed the first specimen was nested within the clade A and the latter two positioned in the clade B. Thus we concluded that these samples were misidentified, with the former being S. grahami and the latter two being S. collaris .
Zhao and Yang (1997), Zhao et al. (1998), Zhao (2006), and Yang and Rao (2008) proposed that S. collaris is distributed in southern Xizang and northwestern Yunnan in China. Based on our molecular phylogenetic analyses, however, several specimens collected from northwestern Yunnan, which is geographically close to Motuo, Xizang, were identified as S. grahami and S. triangularis (Fig. 2). Thus, it is most like that S. collaris is endemic to Motuo in Xizang, with no occurrence in Yunnan.