Molecular verification and phylogenetic placement of leaf-toed geckos (Dixonius: Squamata: Gekkonidae) in Thailand

Dixonius is a monophyletic gekkonid lizard genus endemic to Southeast Asia, with 50% of the described species in the genus occurring within Thailand. In Thailand, several new species were recently described solely based on morphology. However, the phylogenetic position and systematics of these species remain unknown due to a lack of genetic data. To verify the taxonomic status and phylogenetic placement of Dixonius species in Thailand, we obtained and analyzed sequences of the mitochondrial NADH dehydrogenase subunit 2 (ND2) gene from seven nominal Dixonius species (D. dulayaphitakorum, D. hangseesom, D. kaweesaki, D. mekongensis, D. melanostictus, D. pawangkhananti and D. siamensis) collected from their type localities in Thailand. Our results provide the first genetic data of several Dixonius species in Thailand, notably the type species, D. siamensis. The validity of seven nominal Dixonius species in Thailand was confirmed with well-supported lineages. Interestingly, this study reports a new national record of D. somchanhae from Bueng Kan, northeastern Thailand, approximately 100 km from its type locality. This result brings the total number of nominal Dixonius species occurring in Thailand to ten. Furthermore, we found that D. melanostictus and D. cf. siamensis from other populations outside of their type localities should be tentatively considered as undescribed species. Our findings suggest that the diversity of Dixonius in Thailand has been underestimated. Additional specimens and genetic data across their ranges, especially D. chotjuckdikuli, are needed for both molecular and morphological analyses to further clarify the phylogenetic relationships and true diversity of the genus Dixonius in Thailand.