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December 2003: It's not everyday that someone finds a creature that is new to science. But that is exactly what researchers S.D. Biju, of the Tropical Botanic Garden and Research Institute, Kerala, and Franky Bossuyt, of the University of Brussels did. They have reported the discovery of a burrowing frog that is distinct from all hitherto known families of frogs. This discovery was made in the Idukki district of Kerala in the southern Western Ghats. As if the discovery of a new species in an area that has already been the focus of many studies is not exciting enough, phylogenetic DNA analyses indicate that the frog is closely related to the Sooglossidae frog family, found exclusively on two granitic islands in the Seychelles archipelago, 3,000 km. from the Indian mainland, near the island of Madagascar.
The new species has been christened Nasikabatrachus sahyadrensis. Nasika (Sanskrit) for nose, batrachus for frog, and Sahyadri for the creature's habitat in the Western Ghats. The creature was found in a disturbed secondary forest near a cardamom plantation at Kattapanna, at an altitude of 900 m. The Western Ghats is one of the world's eight ‘hottest' hot spots of biodiversity, with a high degree of species endemism (creatures found nowhere else on earth), and this discovery only adds to an already significant list of endemics.
The Sooglossids of Seychelles are themselves considered somewhat of a mystery. There are several hypotheses to explain their origin, one stating that they descended from African frog species. Another theory is that Sooglossidae were present on the Indo-Madagascar plate as it drifted northwards away from Australia and Antarctica. They subsequently became extinct on India and Madagascar, surviving only on the Seychelles. Biju and Bossuyt's phylogenetic studies and dating estimates favour the latter theory, known as the biotic ferry model. Their studies also indicate that Nasikabatrachidae and Sooglossidae diverged well before the separation of India and the Seychelles.
Biju has been studying the amphibian fauna of the Western Ghats for the last 10 years. Most of the present knowledge on Indian amphibian fauna is based on preserved animals, says Biju, with very few fresh collections. “Our present knowledge on Indian amphibian fauna is totally confused. Misapplication of names, incorrect identification and publication of new species without consulting existing type specimens are common problems." His work has included visits to most museums across the world, which had Indian type specimens in their collections. He is presently studying and comparing, with his sketches, over 1,000 specimens kept in the British Museum of Natural History, London, which were collected during the 1800s and early 1900s from India. His present study in the British Museum is as part of a Royal Society, London and Indian National Science Academy fellowship. Biju feels such thorough examination of past work is essential to ensure that he does not repeat past mistakes.
The purple blob
Only 29 families of frogs, with approximately 4,800 species, are known to science. Most of these were named by the mid-1800s; the last time an entirely new species was discovered was as far back as 1926, making this discovery extremely significant. A relatively large frog (about seven cm.), Nasikabatrachus has a bloated appearance, with smooth, black skin, looking, in fact, remarkably like a large purple blob. A snout with a conspicuous white protrusion marks the tip of the pointed, short head. The feet at the end of the short stubby limbs have partial webbing. Its eyes are bordered with light blue, with an orange iris and black pupil. The dorsal parts are bluish black, while the underside is dark greyish.
The divergence of different frog families occurred in the Mesozoic era (251-65 million years ago), around the same time as many mammal families. This was the period when the Indian land mass is thought to have separated first from the rest of the Gondwana supercontinent, leaving behind what is now Africa and South America. As it drifted east, the land mass broke apart further, leaving behind Antarctica-Australia (130 million years ago), Madagascar (90 million years ago) and the Seychelles (65 million years ago). In this scenario, the Indian subcontinent would have served as a ‘biotic ferry', with plant and animal groups on the landmass evolving in isolation for tens of millions of years.
Curiously, India's late Mesozoic fossil record has so far not thrown up any evidence of a biotic ferry model, instead revealing dinosaurs, lizards, mammals and other organisms with close relatives in Africa and South America. This has led to speculation of the possible existence of land bridges between India and Africa, which would permit the spread of species.
However, if Nasikabatrachus diverged from sooglossids 130 million years ago, as seems to be the case, the separation of the continents would not explain its origin… India separated from the Seychelles only 65 million years ago. Thus while Nasikabatrachus' discovery indicates the biotic ferry model, fossil records support the land bridge theory.
Further, studies of other living plants and animals in India also indicate a period of long isolation from African and South American land masses. To explain this discrepancy, it has been proposed that the ‘land-bridges' were more like a chain of islands, which permitted only some groups of organisms to disperse.
The discovery of this species adds invaluably to the evidence of India's past biogeographical isolation. But many questions remain to be answered: Why does Madagascar lack major groups of vertebrates that evolutionary analyses indicate should have been present? Which is more accurate, the biotic ferry or the land bridge model of continental drift? Further research into both living species and fossils will hopefully yield more answers. Provided the habitat in which they live survives.
by Ashish Fernandes, Sanctuary Asia, Vol XXIII No. 6, December 2003
