Color polymorphism, taxonomic confusion and cryptic diversity in the kukri snake Oligodon albocinctus (Cantor, 1839) (Squamata: Colubridae)

The kukri snake Oligodon albocinctus (Cantor, 1839) is a widespread element of the Indo–Himalayan and Indo-Burmese snake fauna with two distinct color patterns. The first and more typical morphotype has light bands with black edges, while individuals of the second morphotype have brown blotches or narrow crossbars. The polychromatic nature of this species has led to considerable taxonomic confusion between O. albocinctus and members of Oligodon occurring in sympatry or parapatry.

In this study, we investigate patterns of genetic and morphological variation in O. albocinctus and explore whether its color morphotypes correspond with genetic structure recovered in earlier studies. Additionally, we re-assess the status of two taxa that have been confused with O. albocinctus in the past— Oligodon juglandifer (Wall, 1909) and the recently synonymized Oligodon lipipengi Jiang, Wang, Li, Ding, Ding & Che in Che, Jiang, Yan & Zhang, 2020.

Our results suggest both the banded and blotched morphotypes of O. albocinctus are genetically identical and lack phylogenetic signal. We recover three divergent clades separated by pairwise distances of 5.8–9.8% based on cytochrome b gene fragments and 1.7–4.2% based on 12s16s ribosomal RNA fragments. One of these clades is geographically restricted to southwest Myanmar (Burma) and was recovered as sister to all other populations of O. albocinctus.

This lineage was supported as a cryptic yet evolutionarily independent lineage by species delimitation analyses, a partial lack of haplotype sharing based on nuclear DNA sequences (recombination activation gene 1), and subtle differences in morphology. To reflect these results, we resurrect the name Simotes amabilis Günther, 1868 from synonymy (as Oligodon amabilis comb. nov.) for the southwest Myanmar clade. Despite moderately high genetic divergence, morphological support for recognizing O. juglandifer and O. lipipengi was inconclusive and both names are considered junior synonyms of O. albocinctus sensu stricto until additional sampling can be conducted.

We present detailed redescriptions of O. albocinctus and O. amabilis comb. nov. and outline diagnostic characters that distinguish each species from chromatically similar congeners.