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Climbing great heights: endemic montane skinks of Southern India

Updated: Dec 18, 2022

Mountains are known to host a disproportionately large amount of biodiversity compared to other landforms. The Western Ghats of India are no different in this regard, comprising a host of unique endemic groups of tetrapods. There are several reasons for this mind-boggling diversity, the most important being how ancient these mountains are! They have existed for millions of years! As a result, they have witnessed volcanic activities, changing climates and forest cover resulting in extinctions and dispersal of multiple groups of animals. Several significant geographic barriers in the form of deep valleys also dissect the Western Ghats causing hindrances in animal movement. Such isolation across thousands or even millions of years results in the formation of range-restricted and often endemic species of biota.

Multiple groups of herpetofauna have been studied in the Western Ghats, none more so than amphibians, snakes, geckos, and agamid lizards. I will, however, talk about how the Western Ghats have given refuge to two endemic genera of skinks that are unique to their wet forests. As the general audience might know, skinks are a group of lizards that are usually small, shiny, and often snake-like. They are typically seen basking in the morning sun or running and wriggling around during warm sunny days. Scientifically, they belong to a family of lizards called Scincidae that comprises close to 1750 species, worldwide! Okay, back to the Ghats.

The two genera of endemic skinks that I mentioned are the blue-tailed skinks of the genus Kaestlea and the cat skinks belonging to the genus Ristella. As strange as their names might sound, there are some obvious reasons for it. As you might guess, Kaestlea has a striking shiny blue tail, more so when these skinks are young. A few species completely lose the bright blue color as they become adults, while in some other species, a lighter shade of blue is retained into adulthood. Under physical stress, skinks tend to lose their tails as a defence mechanism. The blue tail colouration displayed by Kaestlea possibly diverts the predators’ attention and allows these lizards to escape while their predator is left with just a section of the broken tail. Ingenious! These elegant-looking skinks are found in the higher elevations and are frequently encountered under rocks or logs in high-altitude grasslands and stunted forests. The cat skinks or Ristella do not have very colourful tails, and no, they do not look like cats either. However, they possess retractile claws that go inside an extra scale on the finger, almost like felines! The ecological significance for such a unique adaptation is unknown, and I will let you take your guess while I attempt to unravel the mystery myself.

One of the species, Beddome’s cat skink (Ristella beddomii) develops a bright yellow, orange, and black colouration on its sides during the breeding season. Ristella and Kaestlea are often encountered in the same place in similar microhabitats, although the former is primarily spotted in areas containing leaf litter. Given how species-rich and well explored the Western Ghats are, these two genera of skinks are rather depauperate and understudied, with Kaestlea presently containing five and Ristella containing a total of four known species. The last of Kaestlea and Ristella species were discovered way back in 1892 and 1887, respectively, highlighting the lack of organised expeditionary surveys targeted at systematic research towards Indian skinks. The situation, however, is changing, with much new scientific research being carried out on these diminutive and enigmatic lizards.

The five species within Kaestlea are K. beddomii, K. bilineata, K. palnica, K. laterimaculata, and K. travancorica. Together, they span a distribution range from the central to the southern tip of the Western Ghats, with anecdotal observations reported from the southern Eastern Ghats. Ristella, on the other hand, has a slightly wider distribution range, spanning from parts of northern Western Ghats in Goa all the way to the southern Western Ghats. It is not a strict high-altitude specialist; at least one species, R. beddomii, is found in low-elevation wet forests.

The other three species within the genus are R. guentheri, R. rurkii, and R. travancorica, with R. rurkii being the only high-altitude grassland specialist found in the higher reaches of the Anamalais.

Once you cross over from the western side of the Western Ghats to the east and then to its neighbouring mountain chain, the southern Eastern Ghats, the topography changes starkly. The forests become dry and more stunted, and colossal granitic boulders dwarf you, making you question your significance. The terrain is rocky and treacherous, punctuated by thorny bushes; manoeuvring one’s way through the undergrowth can be challenging. Beneath these sun-baked rocks, resides another specialist montane skink — the Asian agile skink of the genus Subdoluseps. Most members of this genus are found in South East Asia, but some have made their way down to southern India. At present, only two species are known from India, the Pruthi’s supple skink (Subdoluseps pruthi) from Chitteri hills of the southern Eastern Ghats and the recently described Nilgiri gracile skink (Subdoluseps nilgiriensis) from the drier parts of Nilgiris. It is very well possible that further systematic work will reveal more of these small, snake-like skinks from the arid mountains of southern India. Mountains and hills are fragile ecosystems; slight alterations can cause significant damage to local fauna. Today, with climate change being prevalent globally, tropical areas such as the south Indian mountains might be more sensitive to temperature changes than temperate areas. While it is easier to track population trends in seemingly popular and conspicuous animals, the secretive and shy skinks mostly go unnoticed. Conversion of forested habitats into plantations and barren rocky terrain into mining or developmental projects severely affects these lizards. The onus is on us herpetologists and researchers to first enumerate the true diversity of these skinks, as understanding the true biodiversity of a region is one of the prime precursors to conservation.

Avrajjal Ghosh

He is currently pursuing a PhD at the National Institute of Science Education and Research (NISER) and trying to answer questions pertaining to the biogeography and systematics of South Indian montane skinks. You might find him hopping from one hill to another, getting bitten by ticks and leeches while he finds ways to search for these diminutive but fascinating lizards.

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