Undescribed Diversity in a Widespread, Common Group of Asian Mud Snakes (Serpentes: Homalopsidae: Hypsiscopus)
Mud snakes (Serpentes: Homalopsidae) are a morphologically diverse family of aquatic snakes distributed from eastern Pakistan, eastward through South Asia, mainland and maritime Southeast Asia, and extending to New Guinea and northern Australia. Some species of homalopsids represent the most abundant tetrapods in aquatic systems in tropical Asia, but with few evolutionary studies investigating their diversity with dense geographic and taxonomic sampling. The genus Hypsiscopus includes two named species that inhabit freshwater systems throughout most of Southeast Asia: H. matannensis of Sulawesi, and the widespread H. plumbea found in rivers, lakes, and rice paddies in the remainder of Southeast Asia. We use a multilocus dataset of two mitochondrial and three nuclear genes with dense sampling of H. plumbea to elucidate the evolutionary history of this genus. We find that H. plumbea is paraphyletic with respect to H. matannensis, with populations around and north of Central Thailand's Khorat Plateau phylogenetically outside of a clade containing H. matannensis and H. plumbea south of the Khorat Plateau. This lineage differs morphologically and genetically from H. plumbea sensu stricto (south of the Khorat Plateau) and H. matannensis. We describe this lineage as a third species of Hypsiscopus based on its phylogenetic position and meristic and color pattern data. This study exemplifies the need to investigate widespread, abundant taxa to better understand the evolutionary histories of aquatic snakes in Southeast Asia.
Distribution map of Hypsiscopus. Shaded regions and points represent known ranges as of this study and sampling localities, respectively. Stars show type localities; note: type locality for H. plumbea is ‘Java'; central coordinate given.
Phylogeny and quantitative statistics of Hypsiscopus. (A) Principal coordinates analysis of H. murphyi (blue) and H. plumbea (green); non-standardized (left) and standardized (right) runs are shown. Both X- and Y-axes represent PC1 and PC2, respectively. (B) Isolation by distance (IBD) plot showing specimen points for H. murphyi and H. plumbea in separate plots, which comprise the gray points in the larger chart. The blue-green points at the top of the larger chart represent interspecific comparisons of H. murphyi and H. plumbea. (C) Concatenated (phased nuclear+mitochondrial) phylogeny of all specimens of Hypsiscopus used in this study. Circles at nodes represent support values: left side = SH-alrt, right side = UF bootstraps. Black halves of a circle indicate high support for the respective support value at that node. See Data Accessibility for tree file. Photo credit of live H. murphyi holotype (NCSM 85490): BLS.
Morphological characters and variation of Hypsiscopus murphyi. (A–D) Holotype of H. murphyi (NCSM 85490) in preservative showing dorsal (A), ventral (B), and right lateral head (C) views, and hemipenes (D). Black scale bars represent 1 cm in panels A and B, and 2 mm in panels C and D. (E) Close-up of rear-fang of H. murphyi (AMNH R-33908). (F) Variation in melanin pigmentation of the infralabials and anterior chin shields: slightly pigmented (left; NCSM 85490) and heavily pigmented (right; ROM 32374). (G) Left two images, variation in dorsal-to-ventral color patten change: sharp (NCSM 85490) and gradual (ROM 30818). Right two images, variation in ventral color pattern: immaculate (NCSM 85490) and mid-ventral halfmoons (ROM 30818). (H) Variation in extent of mid-ventral caudal stripe, with stripe beginning on second subcaudal pair (AMNH R-33908) rather than the 13th subcaudal pair in the holotype (NCSM 85490; panel B).
Populations of Hypsiscopus murphyi in Indochina with sampling localities (points). Mitochondrial phylogenetic tree shown on right; filled node circles represent strong support; number of individuals for the respective clade are given to the left of the tree. Inset plot shows results of the Mantel test (IBD scenario); histogram on top shows the original values of the observed data (diamond) outside of the gray bars that represent the absence of spatial structure. Major lakes and rivers/tributaries (blue) are labeled on map. Light and dark gray areas on map depict higher and lower elevation, respectively. See Data Accessibility for tree file.
Contributor Notes
Associate Editor: W. L. Smith.