SECRETS OF THE SHIELDTAILS

(Resonance, August, 1996)

An Introduction

The Western Ghats are well known for their biodiversity; much has been written and said about their wide array of plants and animals, especially the high degree of endemism, and the rare and endangered mammals. Less however is known about the herpetofauna of these hills. There are 117 species of amphibians, of which about 90 are endemic. Some ,like the tree frogs found in the higher altitudes, are poorly studied. However, the least known amongst the unique fauna of the Western Ghats may well be the shieldtails. The shieldtails are a group of snakes belonging to the family Uropeltidae. These snakes are found in the Western Ghats and Sri Lanka and nowhere else in the world. There are about 45 species belonging to 7 genera, of which 35 are found in the Western Ghats. They are highly colorful snakes, and each species has its own distinct marking. Uropeltids have evaded extensive study because of their excessively secret nature. These snakes are found in the higher reaches of the Western Ghats, usually at 1500 metres or higher. They inhabit the shola forests, which are the natural vegetation of the area. However, they are also found in the different plantations which have become a common feature of the hills. The snakes burrow 1 to 2 metres below the soil, and stay there for much of the year. They only emerge during the rainy season to mate. Besides, they are also nocturnal which makes them even more difficult to observe.

Montane Homes

Uropeltid snakes are generally found in areas of high elevation and low temperature. The Western Ghats, where most of the uropeltids are found, have a short season of 3 to 4 dry months followed by rains from the Southwest monsoon and the Northeast monsoon. Rainfall seems to limit the distribution of the shieldtails, because it affects the development of forest vegetation. The vegetation in the upper reaches of the Western Ghats is of the shola-grassland type. The sholas are tropical montane stunted evergreen forests. The grasslands form the matrix in the landscape and sholas are generally found in the valleys and on hill slopes. The grasslands are spotted with Rhododendron nilagiricum and also feature riverine tracts. The uropeltids are found largely in the forests. Much of the habitat in the Western Ghats has been replaced by plantations of tea, wattle, pine and eucalyptus. Tea plantations were first introduced by the British and have taken over much of the landscape over the past 150 years. In the last 50 to 100 years, the Forest Departments have shown some concern about the protection of the sholas, but the grasslands have been largely ignored, and many of them have been replaced with wattle plantations.

Painting a picture

Uropeltids are small, fossorial, uniformly cylindrical snakes with a tapering head and tail. In fact, they may be mistaken for large earthworms, but their flashy colours are apparent even to the lay observer. The last scale of the tail forms a large shield, with one or two points. These features are believed to be highly adaptive to their lifestyle. The conical head has a keratinised tip and is slender, pointed and round in cross section. The tail is short and blunt and in fact, they are also called `rough tailed snakes'. The tail has a single enlarged and roughened shield, which may be fringed with less modified scales. The skin is superficially smooth and the scales are shiny and iridescent, showing a spectrum from blue to orange. Most of the uropeltids have a black, brown or olive green dorsal surface. They have light or brightly colored lateral lines or blotches, especially on the tail or the neck. The source of the pigments is within the integument. Most uropeltids are extremely beautiful snakes, but their marvelous colours arouse both admiration and fear.

An Adaptationist Eye View

Uropeltids are essentially earth snakes living beneath the soil. Their wedge shaped head serves as their tunneling device. The keratinised ridge facilitates penetration and serves to distribute stress. The head, led by the tip, drives a primary tunnel and the anterior vertebral column, with its S- shaped curvature, provides second stage widening. The snake's mode of tunneling is well suited to travel among root systems. As the uropeltids do live in tropical forests with a high density of woody plants, the soils are likely to have complex root systems and this adaption becomes significant. These burrows are constructed during the rainy season, when the soil is soft. The burrows then harden, and the snakes wander in their network beneath the soil in search of their food, earthworms. The shield on the tail seems to serve for the formation of a plug to close the tunnel. Many shieldtails, when removed from the soil, have been found to have dirt capped caudal shields. The plug should serve to confuse and deter predators of the snakes.

The chemical colours of the snakes are produced by the chromatophores in the dermis. These could be explained by different adaptive arguments such as flash coloration, head mimicry or mimicry of a noxious animal. They could be flash colours; predators tend to avoid bright or flashy colours as these are usually indicative of poisonous animals. The coiling behaviour of the shieldtails is interesting in this context. When excavated, they are found to coil immediately around one's fingers or any available object, and rigidly project their tails. This is seen to happen when they are burrowing. The tails rhythmic movements, coupled with the lateral eyespots and ring in some forms, enhances its similarity to the head. The color pattern of the snakes may resemble some of the small elapid snakes of Sri Lanka. Although these venomous elapids are now too rare to suggest mimicry, the distributions of these snakes my have been greatly affected by agricultural advances in recent times. It is also suggested that the uropeltid coloration mimics that of some poisonous arthropods such as centipedes. The venomous coral snake, Callophis nigrescens, also occurs at a number of localities in the Western Ghats where uropeltids are also found. Though they share the cylindrical body and short tail, Callophis is much longer than uropeltids, and has a different coloration. However, one uropeltid,. Platyplectrurus trilineatus, has a coloration similar to the coral snake.

Finally the structural colors of uropeltids also may be adaptive. They have an axially oriented stripe pattern. Such regular patterns are believed to help in reduction of friction. In uropeltids, they may serve to keep particles from sticking to the surface and also as an anti wetting device.

In the Food Chain

Earthworms seem to form a major part of the uropeltid diet. They may take small quantities of earwigs, termites and caterpillars, but these are not significant. Stomach content analysis has shown that earthworms form 80-90 % of their diet. Coupled with the fact that uropeltid distribution is closely related to the presence and absence of earthworms, they would appear to be an important part of their ecology. Uropeltids are often killed by boars, which encounter them when digging for tubers. Mongoose may also eat these snakes. Birds, such as domestic fowl, pea fowl, jungle fowl and owls of various kinds will feed on uropeltids. Though uropeltids are known to be ovoviviparous, little else is known about their breeding and reproduction. Normal clutches seem to have 3 to 8 eggs, but there is a record of a specimen with 9 embryos. Development takes place in one oviduct, usually the right one.

Family Trees

Carl Gans used multilocus electrophoretic methods and microcomplement fixation comparisons of serum albumin to evaluate phylogenetic relationships and to study aspects of their population biology and biogeography. Species of uropeltids were found to be genetically highly differentiated, as measured by genetic distances. The phylogenetic tree most consistent with the immunological and electrophoretic data showed the Sri Lankan snakes to be monophyletic, and the Indian snakes to be paraphyletic with respect to those from Sri Lanka. A biogeographic scenario seems to indicate an early diversification in India, followed by an invasion into the lowlands of Sri Lanka. Subsequently, the uropeltids evolved in Sri Lanka to occupy montane biotopes there.

Conservation

Uropeltids are a part of the rich array of fauna of the Western Ghats. Their importance is heightened by the high diversity within the group and their endemism. Many species have highly localised distributions, making them even more vulnerable, as a local extinction would mean the extinction of the species. The decline of uropeltids in recent years may be attributed to the spread of plantations in the Western Ghats. Their habitat has been destroyed and the few remaining areas are highly fragmented. These snakes are also killed by humans, as the hill people believe they are poisonous. Uropeltids could be performing important ecological roles; they are able to burrow in extremely hard soils, creating a complex network of tunnels. It is likely that these allow free passage of air to the deep soil and supply atmospheric air to the roots and rootlets of shrubs and trees. Much of the credit for our present knowledge of uropeltids should go to the late Professor M.V. Rajendran, who pionoreed studies in the basic biology and ecology of these uropeltids.. However, it is quite clear that a lot more research needs to be done on this unique group of snakes. It is also evident that they need to be made a conservation priority if we are to preserve an irreplaceable part of our heritage and an important component of the montane ecosystem of the Western Ghats.

Kartik Shanker Centre for Ecological Sciences Indian Institute of Science Bangalore - 560012. India.

Further Reading

Gans, C., 1976. Aspects of the biology of uropeltid snakes. In A.d'A. Bellairs and C.B. Cox (Eds), Morphology and Biology of Reptiles. Linnean Society Symposium Series No.3: 191-204. London: Academic Press.

Rajendran, M.V., 1985. Studies in Uropeltid Snakes. Madurai: Madurai Kamaraj University