A Sri Lankan herp mystery solved: The snake species that was two
Posted on June 18th, 2020

by  Courtesy Mongabay

  • A new study has finally solved a herpetological mystery surrounding Dendrelaphis bifrenalis, a species of bronzeback snake endemic to Sri Lanka.
  • Researchers have established, through morphological differences and DNA sequencing, that the dry-zone populations of the snake are the true D. bifrenalis, and the wet-zone populations are a species new to science: D. Wickrorum.
  • They named the new species in honor of leading herpetologists L.J. Mendis Wickramasinghe, known as Sri Lanka’s Darwin” for the sheer number of species he has described, and his wife Nethu.
  • The study also rights a taxonomic wrong by re-establishing D. effrenis, another bronzeback, as a valid species, based on a 2016 discovery by Wickramasinghe and observations in the wild, after the species was effectively whitewashed from the taxonomic record nearly 80 years ago.

COLOMBO — For nearly a decade, siblings and scientists Dineth Danushka and Suneth Kanishka have been making field visits to study Dendrelaphis bifrenalis, a snake known as the Boulenger’s bronzeback, which is endemic to Sri Lanka. The data that the brothers gathered over time led them to believe there were two distinct populations of the snake, and that, for more than a century, its various populations had been wrongly lumped together as D. bifrenalis.

Now, in their first ever study, published in May in the journal TAPROBANICA, the researchers look to close a long-running taxonomic cold case by splitting up the species: the bronzeback populations of the dry and intermediate zones remain the true D. bifrenalis. And the population in the wet zone is described as a species new to science: D. wickrorum, or Wickramasinghe’s bronzeback, named in honor of leading herpetologist L.J. Mendis Wickramasinghe, known as Sri Lanka’s Darwin” for the sheer number of species he has described, and his wife Nethu.

The more we observed this snake, the more we suspected that there had to be two distinct species, but this needed extensive studies,” Dineth told Mongabay. He and his brother and fellow researchers followed up field observations with extensive study of physical details and traits and DNA sequencing to conclusively establish that these are distinct species.”

The redescribed D. bifrenalis is considered a beautiful snake bearing an unusual color combination. Image courtesy of L.J. Mendis Wickramasinghe.
The redescribed D. bifrenalis is considered a beautiful snake bearing an unusual color combination. Image courtesy of L.J. Mendis Wickramasinghe.

Among the differences between D. bifrenalis and D. wickrorum are the former’s shorter, narrow and pointed snout, larger eyes, longer head, and a distinct temporal stripe stopping just behind it. The stripe on the dry zone species, however, continues behind the neck. The newly described species also has a divided nasal and a ventrolateral stripe that continues down to the tail.

We observed the wet zone species to be calm and often found them inside thickets deeper in the forested areas, whereas the dry zone species showed aggression and were found on the upper branches of trees, sometimes poised to strike,” Dineth said.

While D. bifrenalis has never been recorded at elevations above 300 meters (1,000 feet), the researchers identified a D. wickrorum specimen from an elevation of 1,000 m (4,000 ft).

The researchers also identified different threats faced by the two species. The dry zone species, D. bifrenalis, is considered vulnerable, while the wet zone species, D. wickrorum, is considered to be of least concern.

For the latter, the biggest threats come from the clearance of forests in Sri Lanka’s wet zone, driven by the expansion of farmland. In the dry zone, the restoration of water reservoirs and other human activity pose the biggest threats to the habitat.

The newly described wet zone species D. wickrorum is named in tribute to the remarkable contributions to the field of herpetology in Sri Lanka by L.J. Mendis Wickramasinghe and his partner, Nethu. Image courtesy of L.J. Mendis Wickramasinghe.
The newly described wet zone species D. wickrorum is named in tribute to the remarkable contributions to the field of herpetology in Sri Lanka by L.J. Mendis Wickramasinghe and his partner, Nethu. Image courtesy of L.J. Mendis Wickramasinghe.

Righting a taxonomic wrong

With their new paper, the scientists also hope to do justice to another Dendrelaphis species, one that was whitewashed out of the taxonomic record.

D. effrenis was first described by the Austrian zoologist Franz Werner, in German, from a single specimen collected in 1909. In 1921, the British herpetologist Frank Wall provided a description in English, but considered the species a likely aberrant specimen of D. caudolineolatus, known as the striped bronzeback. The specimen had been lost by 1943 when another Englishman, Malcolm Smith, synonymized Werner’s species with D. caudolineolatus without any discussion,” the new study says, and subsequent authors followed that taxonomic treatment.”

So for nearly 80 years, D. effrenis never existed. Then, in 2016, none other than Sri Lanka’s Darwin, Wickramasinghe, described what was then believed to be a new species, Dendrelaphis sinharajensis, from the Sinharaja forest, a UNESCO World Heritage site. (Dineth and Suneth credited Wickramasinghe’s enormous effort in popularizing snake conservation among the general public.”)

Species review underway with veteran herpetologist and taxonomist A.A. Thasun Amarasinghe and evolutionary ecologist Sampath S. Seneviratne. Image courtesy of Sameera Suranjan Karunarathna.
Species review underway with veteran herpetologist and taxonomist A.A. Thasun Amarasinghe and evolutionary ecologist Sampath S. Seneviratne. Image courtesy of Sameera Suranjan Karunarathna.

A comparison of [that specimen] and the original description of D. sinharajensis with the original description of D. effrenis revealed that both names were created for the same species,” the study says. Therefore here we revalidate D. effrenis as a distinct species of the genus Dendrelaphis [and] we synonymise D. sinharajensis with D. effrenis.”

Not only did the scientists bring D. effrenis back to life on paper — they also observed two specimens in the wild, giving them a better understanding of the species’ range.

The fact that they were able to describe a new species, and even bring one back from the dead, highlights the need for further studies of Sri Lanka’s bronzeback snakes, the researchers say.

It is high time for a comprehensive phylogenetic study for this divergent, ecologically complex genus,” they write in the study, to understand not just the phylogenetic affinities of its members, but also its colonization patterns across Southern and Southeastern Asia.”

Citation:

Danushka, A. D., Kanishka, A. S., Amarasinghe, A. A., Vogel, G., & Seneviratne, S. S. (2020). A new species of Dendrelaphis Boulenger, 1890 (Reptilia: Colubridae) from the wet zone of Sri Lanka with a redescription of Dendrelaphis bifrenalis (Boulenger, 1890). TAPROBANICA9(1), 83-102.

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