Amphibians

The purple frog spends most of the year underground, surfacing only for about two weeks during the monsoon season in order to mate. It lives 1.3-3.7m below ground and the frog's reclusive fossorial (digging or burrowing) lifestyle is what caused the species to escape earlier detection by biologists. It comes to the surface for a few weeks a year to breed in temporary and permanent ponds and ditches. During the breeding season, local people reported seeing purple frogs in the vicinity of water pools or at the sides of the swelling streams in pairs clasping each other, especially at the beginning of the monsoon season. During mating, the male clasps the female from behind just above the legs in a behaviour termed “inguinal amplexus”. The bloated shape of both male and female purple frogs, and the smaller size of the male, may mean that males partially glue themselves onto females using sticky skin secretions, as occurs in “short-headed frogs” in the family Brevicipitidae. Eggs are laid in water that hatch into tadpoles, often in ponds close to streams.

The diet of the purple frog predominantly consists of termites, and this species has a narrow mouth with a small gape, preventing it from catching and consuming larger prey items. Its strong head and pointed snout permits it to penetrate underground termite niches, and a fluted tongue may allow this species to suck up its prey from subterranean burrows. With its poor vision, this frog presumably depends on smell and tactile cues to detect and locate prey. It also consumes ants and small worms.

The burrowing and mound-building activities of termites increase the rate of percolation of rainwater and aeration of both the top and subsoil keeping the underground soil temperature low and the moisture content high. It may therefore benefit burrowing amphibians like the purple frog to live in close proximity to termite colonies, which improve the quality of their habitat as well as providing a food source. In India, the purple frog from the southern Western Ghats may be the only known amphibian species that is a fully underground forager. All other burrowing frogs are either open burrow feeders or diurnal burrow dwellers that are open ground feeders in the night.

Purple frogs require damp, loose soil to borrow into, and may dig themselves fully into appropriate soil within 3 to 5 minutes. When placed on hard ground, pebbled- or gravel-strewn soil, or areas with a thick mat of weeds, purple frogs are unable to borrow effectively and go in search of cover. The hind limbs have strong feet with wart-like structures that are primarily used for digging. This frog burrows downwards using its hind limbs like spades, throwing the soil over its back. They rest underground in a horizontal position with the limbs tucked under the body, although they do not remain idle underneath the soil, especially when foraging for their prey.

The first purple frog was officially discovered in disturbed secondary forest near a cardamom plantation. It has also been found in disturbed secondary forest contiguous with montane evergreen forest. It presumably occurs in undisturbed forest as well and apparently does not survive in open, completely clear habitats. This species requires fairly loose, damp, well-aerated soil, especially in close proximity to termite colonies.

The purple frog is thought to be a rare species, although it is very hard to find which makes any population estimate difficult to determine. Only 135 individuals have so far been observed, and of these only three have been females. The plantation workers within the range of this species have reported that this frog is uncommonly found when they are cutting trenches during the monsoon period (June to October).

The purple frog is thought to be in decline by the IUCN Red List of Threatened Species.

The purple frog is listed as Endangered in the IUCN Red List of Threatened Species because its extent of occurrence is less than 5,000 km sq., all individuals found are in fewer than five locations, and there is a continuing decline in the extent and quality of its habitat in the Cardomom Hills, Western Ghats.

The main threat to the purple frog is believed to be ongoing forest loss for coffee, cardamom, ginger and other species for cultivation.

It has not yet been found in any protected areas, although its range is an integral part of the peripheral hilly area that adjoins the Silent Valley National Park. There are no specific conservation measures ongoing for this species.

The conservation of suitable habitat for this species should involve working with local plantation owners to encourage ecologically sensitive farming techniques. Establishing a reserve for this species, or extending the boundary of the Silent Valley National Park to encompass part of the range of the purple frog could be beneficial if the protect area is appropriately managed. More research into the environmental requirements and range of this species, in addition to regular population surveys, are also vital components of any conservation project for the purple frog, and all information collected should be used to develop a Conservation Action Plan for this species and its habitat.

Developing an environmental education programme for the communities, farmers and plantation workers within the range of the purple frog would help increase local knowledge and pride in this species, especially if it can be made a symbol of local biodiversity. This could also enable local stakeholders to become involved in conserving through learning about more ecologically sensitive land uses and how to set aside some areas for this species.

AmphibiaWeb

Amphibians of Sahyadri

Genome News Network: Purple frog pops up

Global Amphibian Assessment

BBC news: Purple frog delights scientists

Tree of Life Web Project

VUB (Free University of Brussells/Vrije Universiteit Brussel) Amphibian Evolution Lab: S.D. Biju

AmphibiaWeb: Information on amphibian biology and conservation [web application]. 2006. Berkeley, California: AmphibiaWeb. Available: . Accessed: 08 December 2006.

Biju, S.D. and Bossuyt, F. 2003. New frog family from India reveals an ancient biogeographical link with the Seychelles. Nature 425: 711-714.

Biju, S.D. 2004. Nasikabatrachus sahyadrensis. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. . Downloaded on 16 May 2007.

Duellman, W. E. and Trueb, L. 1986. Biology of Amphibians. McGraw-Hill, New York.

Dutta, S.K., Vasudevan, K., Chaitra, M.S., Shanker, K. and Aggarwal, R.K. 2004. Jurassic frogs and the evolution of amphibian endemism in the Western Ghats. Current Science 86(1): 211-216.

Frost, Darrel R. 2006. Amphibian Species of the World: an Online Reference. Version 4 (17 August 2006). Electronic Database accessible at: . American Museum of Natural History, New York, USA.

Frost, D. R., Grant, T., Faivovich, J., Bain, R.H., Haas, A., Haddad, C. F. B., De Sá, R.O., Channing, A., Wilkinson, M., Donnellan, S.C., Raxworthy, C.J., Campbell, J.A., Blotto, B.L., Moler, P., Drewes, R.C., Nussbaum, R.A., Lynch, J.D., Green, D.M., and Wheeler, W.C. 2006. The Amphibian Tree of Life. Bulletin of the American Museum of Natural History 297: 1-370.

Halliday, T. and Adler, C. (eds.). 2002. The new encyclopedia of reptiles and amphibians. Oxford University Press, Oxford.

Hedges, S.B. 2003. The coelacanth of frogs. Nature 425: 669-670.

IUCN, Conservation International and NatureServe. 2006. Global Amphibian Assessment. . Accessed on 08 December 2006.

Obst, F.J., Richter, K. and Jacob, U. 1984. The Completely Illustrated Atlas of Reptiles and Amphibians for the Terrarium. T.F.H. Publication Inc., N.J., U.S.A.

Radhakrishnan, C., Gopi, K.C. and Muhamed Jafer Palot. 2007. Extension of range of distribution of Nasikabatrachus sahyadrensis Biju & Bossuyt (Amphibia: Anura: Nasikabatrachidae) along Western Ghats, with some insights into its bionomics. Current Science 92(2): 213-216.

Roelants, K., Gower, D. J., Wilkinson, M., Loader, S. P., Biju, S. D., Guillaume, K., Moiau, L. and Bossuyt, F. 2007. Global patterns of diversification in the history of modern amphibians. Proceedings of the National Academy of Sciences 104: 887-892.