Redescription and systematics of Oligodon ornatus Van Denburgh, 1909, and two enigmatic related species (Squamata, Colubridae)

On the basis of molecular and morphological data, we re-evaluate the systematics of three closely related species of Oligodon Fitzinger, 1826 with unclear relationships: Oligodon ornatus Van Denburgh, 1909, Oligodon lungshenensis Zheng & Huang, 1978, and Oligodon bivirgatus Qian, Qi, Shi, Lu, Jenkins, Mo & Li, 2021. Recent phylogenetic studies recovered two divergent lineages of O. ornatus that render this species paraphyletic relative to O. bivirgatus.

An examination of genetically identified material indicates that one of the two clades represents O. ornatus, while the other represents O. lungshenensis, thus resolving the paraphyly. Detailed descriptions of hemipenial morphology for all three species are provided, and all three species are redescribed and re-diagnosed, providing an updated framework for their identification. One male O. bivirgatus exhibits a color pattern differing from the type series, but this variation is likely intraspecific in nature as it does not correspond with sexual dimorphism.

While mitochondrial DNA sequences revealed low to moderate pairwise genetic distances between species, haplotype networks from three nuclear loci recover limited evidence of allele sharing. We interpret these results as supporting the continued recognition of all three taxa as recently diverged yet distinct units at the species level. A unique temporal scale configuration observed in several Oligodon is discussed.