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| Oligodon rostralis
Nguyen, Tran, Nguyen, Neang, Yushchenko & Poyarkov, 2020
DOI: 10.7717/peerj.8332
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Abstract
We describe a new species of Oligodon from the highlands of the Langbian Plateau, southern Truong Son Mountains, Vietnam, based on morphological and molecular phylogenetic analyses. The new species, Oligodon rostralis sp. nov. is distinguished from its congeners by the following morphological characters: medium size in adults (male TL = 582 mm); small and broad head with long protruding snout; dorsal scale row formula 15-15-13; 167 ventrals, 47 subcaudals; single preocular, single postocular; loreal and presubocular absent; six supralabials, third and fourth entering orbit; six infralabials, anterior four contacting first pair of chin shields; internasals separate from prefrontals; nasal divided; single anterior and two posterior temporals; cloacal plate undivided; hemipenes short, bilobed, bifurcating in anterior one third of their length, extending to 8th subcaudal, lacking spines and papillae, with a prominent transverse flounces and distal calyces; six maxillary teeth, the posterior three enlarged; dorsal pattern consisting of 14+4 large dark-brown blotches and a bright-orange vertebral stripe on tail and dorsum; and ventral surfaces in life cream laterally with dark quadrangular spots; dark temporal streak present, edged with white. We also provide additional information on O. annamensis, including a morphological dataset of all specimens known from natural history collections and confirmation of an earlier record of O. annamensis from Cambodia. We also provide the first record of O. annamensis for Dak Lak Province. Phylogenetic analyses of mtDNA genes (3,131 bp of 12S rRNA, 16S rRNA and cyt b) suggest sister relationships of Oligodon rostralis sp. nov. and O. annamensis and place them in one clade with the O. cyclurus and O. taeniatus species groups, which is concordant with previous studies on the phylogenetic relationships of Oligodon. Our study demonstrates high level of herpetofaunal diversity and endemism of Langbian Plateau and further supports the importance of this area for conservation herpetofaunal diversity in Indochina.
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| Figure 4: Drawings (A, C, E) and photos (B, D, F) showing head scalation of the holotype Oligodon rostralis sp. nov. in preservative (SIEZC 20201, male). (A, B) Dorsal view; (C, D) lateral view; (E, F) ventral view. Scale bar equals 5 mm. Drawings and photos by Linh Hoang Nguyen. |
Oligodon rostralis sp. nov.
Diagnosis. The new species is assigned to the genus Oligodon Fitzinger, 1826 on the basis of its phylogenetic position and the following morphological attributes: posterior maxillary teeth enlarged and compressed; head short, barely distinct from neck; eye well-developed with round pupil; rostral enlarged; body cylindrical with smooth scales; ventrals rounded; subcaudals paired. Oligodon rostralis sp. nov. is distinguished from its congeners by a combination of the following morphological characters: medium size in adults (male TL = 582 mm); head small and broad with long largely protruding snout; 15 dorsal scale rows at neck and midbody and 13 rows before vent; ventrals 167, subcaudals 47 in male; single preocular, single postocular; loreal and presubocular absent; six supralabials, third and fourth entering orbit; six infralabials, anterior four contacting chin shields; internasals separate from prefrontals; nasal divided; single anterior and two posterior temporals; cloacal plate undivided; comparatively short hemipenis, forked in anterior one third of their length, extending to 8th subcaudal, lacking spines and papillae, bearing prominent transverse flounces and distal calyces; six maxillary teeth, the posterior three being enlarged; dark temporal streak present, edged with white; 14+4 large dark-brown dorsal blotches; bright-orange vertebral stripe on tail and dorsum; and ventral surfaces in life cream with quadrangular spots.
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| Figure 6: Holotype of Oligodon rostralis sp. nov. in life in situ (SIEZC 20201, male) in dorsal (A) and in frontal (B) views. Photos by Linh Hoang Nguyen. |
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| Figure 7: Natural habitat of Oligodon rostralis sp. nov. at the type locality in pine forest dominated by Pinus kesiya Royle ex Gordon in Bidoup–Nui Ba NP, Lam Dong Province, Langbian Plateau, southern Vietnam. (A) Live ventral coloration of Oligodon rostralis sp. nov. (SIEZC 20201, male); (B) general view of the macrohabitat (elevation 1,622 m a.s.l.). Photos by Linh Hoang Nguyen. |
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| Figure 1: Known distribution of Oligodon annamensis Leviton, 1953 (red) and Oligodon rostralis sp. nov. (yellow) in Indochina. Star and dot in the center of icon denotes type locality. Localities: (1) Bidoup-Nui Ba NP, Lam Dong Province, Vietnam (type locality of Oligodon rostralis sp. nov.); (2) Bao Loc (formerly “Blao, Haut Donai”), Lam Dong Province, Vietnam (type locality of O. annamensis); (3) Chu Yang Sin NP, Dak Lak Province, Vietnam; (4) Phnom Samkos WS, Pursat Province, Cambodia. |
Etymology. The specific name “rostralis” is a Latin adjective in the nominative singular, masculine gender, derived from Latin words “rostrum” for “snout” or “beak” in reference to protruding snout distinctive for the new species. We suggest the following common names for the new species: “Long-snouted kukri snake” (English), “Răn khiêm mõm dài” (Vietnamese), and “Dlinnorylyi oligodon” (Russian).
Distribution. At present the new species is known only from the type locality in Bidoup–Nui Ba NP, in the eastern part of Langbian Plateau, southern Vietnam (see Fig. 1, locality 1). This montane area is characterized by high levels of local endemism (Nazarov et al., 2012; Poyarkov et al., 2014; Poyarkov et al., 2015a; Poyarkov et al., 2015b; Poyarkov et al., 2017; Poyarkov et al., 2019b; Stuart et al., 2011; Rowley et al., 2016); further research is needed to clarify the distribution of the new species.
Habitat and natural history. The type specimen was collected on the steep slope close to the mountain summit (Fig. 7), at late night (23 h). The animal was found on ground in leaf litter on the edge of the mixed-pine forest (dominated by Pinus keysia Royle ex Gordon) and evergreen montane broadleaf forest (dominated with trees of the families Fabaceae, Fagaceae, and few large pine trees of Pinus keysia, with understory consisting mostly of Poaceae –different species of bamboo) (Fig. 7B). In the pine forest, understory is dominated by Fagaceae family while ground is covered mostly by grasses and receives high grazing impact by livestock from the villages nearby. In the type locality the new species was recorded in sympatry with some other species of reptiles, including Cyrtodactylus bidoupimontis Nazarov, Poyarkov, Orlov, Phung, Nguyen, Hoang & Ziegler, Scincella rufocaudata (Darevsky & Nguyen), and Pareas hamptoni (Boulenger).
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| Figure 10: Specimen of Oligodon annamensis Leviton, 1953 from Chu Yang Sin NP, Dak Lak Province, southern Vietnam, in life (ZMMU R-14304, male). (A) General dorso-lateral view; (B) general ventral view; (C) head in dorsal view; (D) head in ventral view. Photos by Nikolay A. Poyarkov. |
Oligodon annamensis Leviton, 1953
Revised diagnosis. An Oligodon with medium body size in adults (adult male TL up to 412 mm); head small, comparatively narrow, snout not protruding; 13 dorsal scale rows at neck, midbody and before vent; ventrals 146–157, subcaudals 43–46 in males; ventrals 170, subcaudal 30 in female; single preocular, single postocular; loreal and presubocular absent; generally six supralabials, third and fourth entering orbit; six infralabials, anterior three or four contacting the first chin shield; internasals separate from prefrontals; nasal entire; single anterior and one or two posterior temporals; cloacal plate entire; hemipenis deeply bilobed, bearing two long and thin papillae, reaching the 20th subcaudal; 7–8 maxillary teeth; broad dark temporal streak; ground color on dorsum dark brown, 9–10+2–5 light crossbars edged with black on dorsum and tail; vertebral stripe absent; and ventral surfaces in life coral-red to orange with black transverse bars or quadrangular spots.
Distribution. To date O. annamensis is reliably known from two provinces of southern Vietnam (Lam Dong and Dak Lak), where it was recorded in montane forests of Langbian Plateau at elevations around 1,000 m a.s.l., and from similar elevations in montane forests of Phnom Samkos Mt. in the western part of the Cardamoms, Pursat, Cambodia. The record of O. annamensis from Dak Lak Province is a range extension and the first provincial record of this species.
Etymology. The specific name “annamensis” is a Latin adjective derived from “Annam”, the historical name of Truong Son Mountains and central Vietnam. Common name in English: “Leviton’s kukri snake” (English), “Răn khiêm trung bo” (Vietnamese), and “Annamskiy oligodon” (Russian).
Conclusions:
Here, we present new molecular sequence data and an updated mtDNA genealogy for the genus Oligodon, one of the most species rich groups of Asian snakes. We confirm the presence of four main clades within the genus Oligodon, and for the first time report on the phylogenetic placement of several poorly known Oligodon species, including O. annamensis and O. lacroixi. We analyze all available collection material of O. annamensis from southern Vietnam and Cambodia and confirm the earlier assignation of Cambodian population from Cardamom Mountains to this species based on both morphological and molecular lines of evidence. Finally, we report on a new species of Oligodon from southern Vietnam, known from a single male specimen. Oligodon rostralis sp. nov. is distinct from all other congeners in a number of morphological diagnostic characters and is morphologically and phylogenetically most closely related to O. annamensis, from which it can be easily distinguished in scalation, coloration and mtDNA sequences. We analyze available morphological data on Oligodon species with 15 or 13 dorsal scale rows occurring in the mainland Asia, and discuss phylogenetic relationships among them. We provide further evidence for an unprecedented herpetofaunal diversity and endemism in Langbian Plateau, Southern Vietnam.
Hung Ngoc Nguyen, Bang Van Tran, Linh Hoang Nguyen, Thy Neang, Platon V. Yushchenko and Nikolay A. Poyarkov. 2020. A New Species of Oligodon Fitzinger, 1826 from the Langbian Plateau, southern Vietnam, with Additional Information on Oligodon annamensis Leviton, 1953 (Squamata: Colubridae). PeerJ. 8:e8332. DOI: 10.7717/peerj.8332
