The next time you hear something about the Sri Lankan cat snake’s (Boiga ceylonensis) population from India, be skeptical, for it could be a case of mistaken identity, advise researchers on the back of a discovery of a cat snake species from India.
The latest addition to the cat-eyed Boiga genus, Thackeray’s cat snake (Boiga thackerayi sp. nov), described in a paper in the Journal of the Bombay Natural History Society, is genetically distinct but looks like (is morphologically similar to) the Sri Lankan cat snake.
“This discovery from the northern Western Ghats is going to change our ‘historical perception’ of Boiga ceylonensis from India,” Varad Giri, director of the Pune-based Foundation for Biodiversity Conservation and one of the authors of the paper, told Mongabay-India.
Boiga is one of the most diverse colubrid genera that occur in the Indian subcontinent. (Colubridae is the largest snake family and includes about two-thirds of all known living snake species). Of the 34 species of Boiga currently regarded as valid, 16 are known from India and five from Sri Lanka.
Thackeray’s cat snake (Boiga thackerayi sp. nov) with its tiger-like stripes is the first known species of Boiga that feeds on frog eggs and exclusively eats climbing frogs. This is the second species of Boiga, after B. dightoni, that is endemic to the Western Ghats and the first new species of Boiga described after 125 years from the Western Ghats.
The discovery highlights the importance of cryptic diversity (when two or more distinct species that are lumped together as a single one because they look very similar) and implications in conservation measures.
“If you look at the identification of so-called Boiga ceylonensis is India, it is merely based on morphology. The type locality (the place from where the first individuals were used in describing this species) of B. ceylonensis is Ceylon (Sri Lanka). Eventually, individuals observed in India, that have ‘similar’ morphological features, were also considered as the same species,” said Giri.
“So the apparent distribution of B. ceylonensis is Sri Lanka and the entire Western Ghats,” he said.
The first individual of the cat snake was spotted in Koyna Wildlife Sanctuary, which is part of the Sahyadri Tiger Reserve in the west Indian state of Maharashtra. It was named after Tejas Thackeray for his contribution to the find.
Most of the earlier and recent studies indicate that the species that occur in wet zones in India and Sri Lanka show endemism and are confined to respective landscapes. The species which are in the dry zones are widely distributed and are known from both the countries.
“The B. ceylonensis and B. thackerayi both are endemic to the Western Ghats, hence we decided to check their phylogenetic positions. And the genes provided a real story, where it is proved that both these species are genetically very distinct and ‘unrelated’, not the same as morphology suggests,” said Giri.
“In the future, all the populations considered as B. ceylonensis from India will be taken with a pinch of salt,” he pointed out.
Sri Lankan herpetologist D.M.S. Suranjan Karunarathna commended the identification. He told Mongabay-India that identification of Indian species will be extremely helpful to pin-point Sri Lankan counterparts as well.
Two of a kind
The morphological similarity between Sri Lankan cat snake and Thackeray’s cat snake is due to their proclivity to a specific habitat. “By being arboreal (living in trees) the snakes of the genus Boiga are habitat-specific and have a set of morphological characters that suit them in being so. This selection pressure which is similar across their range would have resulted in morphological conservatism and cryptic diversification, ‘forcing’ them to look similar,” explained Giri.
The researchers underscore the use of more evidence when dealing with the identification of species, especially for cryptic species.
It took almost took 15 years for the researchers to ascertain Thackeray’s cat snake’s true identity after an individual of the species was first spotted in 2005. The researchers were being cautious with the taxonomic identification that was supported by molecular data.
“In dealing with cryptic species one needs to be confident about the proper identity of species you are dealing with. I did not want to rush with limited understanding. Hence I contacted Frank Tillack (of Leibniz Institute for Research on Evolution and Biodiversity) who is an authority on this group. He provided me with the morphological data of type specimens of all Boiga species. This was needed to confirm the identification,” Giri added.
The first individual of the cat snake was spotted in Koyna Wildlife Sanctuary, which is part of the Sahyadri Tiger Reserve in the west Indian state of Maharashtra. It was named after wildlife researcher Tejas Thackeray for his contribution to the find. The cat snake’s tiger-like stripes are also reflective of the political party Shiv Sena’s (which Tejas Thackeray father leads) symbol, the tiger.
“The first individual of this snake, which was a baby, was spotted by me in 2005 near a stream in Koyna. Then it fell from a tree next to us when we were doing a nocturnal survey to study breeding behaviour of an endemic frog, Nyctibatrachus humayuni. Then Tejas Thackeray spotted a few more individuals and this time adults. He realised that this snake looks very different and for further observation collected a few individuals,” Giri elaborated.
Tejas Thakeray, who had necessary permits, observed that they are always seen close to the streams in Koyna Wildlife Sanctuary. He sent those specimens to Giri for further studies.
“The specimens on which we described the species were collected by Tejas, he provided crucial information about their natural history and habitat and he supported us in doing this study in providing much-needed support,” said Giri acknowledging Thackeray’s contributions.
While most of the cat snakes in India are generally known to feed on lizards, birds, and frogs, this was the first report of cat snake feeding on eggs of frogs.
During monsoons, forest streams in the northern Western Ghats, where this snake is seen are “flooded” with the Humayun’s wrinkled frogs (Nyctibatrachus humayuni), the researcher noted.
“These frogs are again ‘exclusive’ in laying their eggs outside water, on leaves, rocks, stems, and overhanging stems. Their number is large and naturally their eggs as well. This large amount of ‘protein supply’ in their habitat would have been an easy diet for these snakes,” Giri reasoned.
The apparent habitat specificity also made this snake ‘choosier’ in its diet. A single individual kept in captivity for observations only fed on frogs which are good climbers e.g. Indian leaping frog (Indirana sp.), common tree frog (Polypedates maculatus) and Ghate’s bush frog (Raorchestes ghatei). It avoided geckos and other terrestrial species of frogs, the authors note.
Plug the gap in reptilian studies in India
With Thackeray’s cat snake slithering its way into the limelight, researchers feel the discovery (as well as others prior to this) should catalyse efforts to expand understanding of reptiles in India.
“Reptiles are poorly studied in India and for the amount of diversity of reptiles we have, there are a few dedicated efforts to document this diversity. Our present-day understanding of reptile diversity is mainly based on historical studies with limited and dedicated efforts in recent years. This understanding has many lacunae as the understanding of taxonomy is revised with the advent of recent tools like molecular phylogeny,” said Giri.
The dedicated efforts in the last decade on frogs and a few groups of lizards proved that our historically understanding of Indian reptiles was wrong as it is composed of cryptic species diversity, especially in the context of biogeography, maintained Giri. Efforts on studying frogs and lizards resulted in the description of many new species as there were genetically distinct.
“We now know that many supposedly widely distributed species are species complexes. We do have 10 biogeographic zones in India and every region has its own biogeographic history. The new discovery of snake also highlights that similar kind of work is warranted for snakes as well,” he said.
The Western Ghats is a ‘biodiversity hotspot’ and is considered as one of the well-explored landscapes. But in the last two decades, a new family and many more new species of amphibians and reptiles were described from the Western Ghats.
“Discoveries like this highlight the importance of this landscape. The northern Western Ghats are considerably ‘poor’ in terms of species diversity and endemicity as compared to the southern part. The presence of species like B. thackerayi proves the uniqueness of this landscape highlighting its conservation,” Giri added.