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| Trimeresurus ayeyarwadyensis Chan, Anuar, Sankar, I.T. Law, I.S. Law, Shivaram, Christian, Mulcahy & Malhotra, 2023 |
Abstract
In a genomic study by Chan and colleagues, pit-vipers of the Trimeresurus erythrurus–purpureomaculatus complex from the Ayeyarwady and Yangon regions in Myanmar were demonstrated to be a distinct species based on robust population genetic and species delimitation analyses. Here, we provide morphological characterizations and a formal description of those populations as a new species. The new species, Trimeresurus ayeyarwadyensis sp. nov., is most closely related to T. erythrurus and T. purpureomaculatus and shares morphological characteristics with both of those species. Some specimens of T. ayeyarwadyensis sp. nov. have green dorsal coloration and no distinct dorsal blotches (a trait shared with T. erythrurus but not T. purpureomaculatus), while others have dark dorsal blotches (a trait shared with T. purpureomaculatus but not T. erythrurus). The distinct evolutionary trajectory of the new species, coupled with the lack of obvious morphological differentiation, represents a classic example of the cryptic nature of species commonly found in the Trimeresurus group of Asian pit-vipers and underscores the need for data-rich analyses to verify species’ boundaries more broadly within this genus.
Key words: Cryptic species complex, mangrove pit-viper, morphology, snake, systematics, taxonomy
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| Photographs of an unvouchered, live specimen of Trimeresurus ayeyarwadyensis sp. nov. from the Yangon Region, Myanmar (Photos by Wolfgang Wüster). |
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| Trimeresurus species in Myanmar A Trimeresurus ayeyarwadyensis sp. nov. (CAS 213410) from Hlawga Wildlife Park, Yangon Region (photo by CAS-Myanmar Herpetology Survey team, CAS-MHS) B T. erythrurus (CAS 235958) from Phalum District, Chin State (photo by Hla tun) C T. ayeyarwadyensis sp. nov. (CAS 219764) from Meinmahla Kyun Wildlife Sanctuary, Pyapon District, Ayeyarwady Region (photo by Hla tun) D T. ayeyarwadyensis sp. nov. (CAS 212245) from Mwe Hauk Village, Ayeyarwady Region (photo by Dong Lin). |
Trimeresurus ayeyarwadyensis sp. nov.
Vernacular name: Ayeyarwady pit viper
Diagnosis: Trimeresurus can be distinguished from all other Asian pit-vipers by the condition of the first infralabial and nasal scale, which are at least partially fused. The new species can be diagnosed from other species of Trimeresurus by the following combination of characters: in both sexes (n = 19), 23–25 dorsal mid-body scale rows (mean 24.3 ± 0.97), 17 scale rows just anterior to vent (rarely 15 or 16) and body scales distinctly and sharply keeled; in males (n = 8), 150–170 ventral scales (mean 160.6 ± 5.6), 71–76 subcaudal scales (mean 73 ± 1.8); a minimum of 9–11 scales between supraoculars (mean 9.9 ± 0.6); between 5–9 scales touching the subocular scale (not counting pre- and post-oculars; mean 6.9 ± 0.9); supralabials 9–12 (mean 10.4 ± 0.8). In females (n = 11), 157–174 ventral scales (mean 165.1 ± 4.9), 52–58 subcaudal scales (mean 55 ± 2.1); a minimum of 10–12 scales between supraoculars (mean 10.8 ± 0.9); between 5–8 scales touching the subocular scale (not counting pre- and post-oculars; mean 6.5 ± 0.8); supralabials 10–12 (mean 10.9 ± 0.6).
Distribution: Trimeresurus ayeyarwadyensis sp. nov. occurs at Hlawga Park in the Yangon Region and Pyapon and Myaungmya districts in the Ayeyarwady Region. The northern and western limits of its distribution likely lie somewhere in between the Myaugmya and Pathein districts in the Ayeyarwady Region. Southward, it could occur in mangroves in Mon State.
Natural history: In the Pyapon and Myaungmya districts in the Ayeyarwady Region, snakes were found in mangrove forests, whereas at Hlawga Park in the Yangon Region, snakes were found in forested habitats around a lake that is not connected to any mangrove system. In that regard, T. ayeyarwadyensis sp. nov. is more similar to T. erythrurus as opposed to T. purpureomaculatus, which is a strict mangrove-associated species.
Etymology: The specific epithet “ayeyarwadyensis” refers to the Ayeyarwady River (= Irrawaddy River), which is the largest and one of the most important rivers in Myanmar. The river forms an expansive delta that is bounded by the Pathein River to the west and the Yangon River to the east. These rivers and their associated basins also mark the westernmost and easternmost distribution boundaries of T. ayeyarwadyensis sp. nov.
Kin Onn Chan, Shahrul Anuar, Ananthanarayanan Sankar, Ingg Thong Law, Ing Sind Law, Rasu Shivaram, Ching Christian, Daniel G. Mulcahy and Anita Malhotra. 2023. A New Species of Pit-viper from the Ayeyarwady and Yangon regions in Myanmar (Viperidae, Trimeresurus). ZooKeys. 1186: 221-234. DOI: 10.3897/zookeys.1186.110422
