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Researchers say the discovery makes the island, which covers more than 65,000 square kilometres, an amphibian hotspot of global significance.

A team of US, Belgian and Sri Lankan scientists recorded the new frogs as they surveyed the island's disappearing wildlife.

Writing in the journal Science, the researchers led by Madhava Meegaskumbura, from the University of Boston in Massachusetts, US, called for the preservation of Sri Lanka's remaining forest fragments as well as habitat restoration.

"The simultaneous discovery of more than 100 species is…astonishing news," said David Skelly of Yale University's School of Forestry and Environmental Studies in New Haven, Connecticut. "Sri Lanka is relatively small and relatively well known compared to much of the tropics," he said. The discovery "is testimony to how little we know about the distribution of biodiversity."

Five of the new species are tree frogs that lay eggs in homespun foam baskets suspended above water—from whence the tadpoles take their first dip. The remainder are all species that produce young on the forest floor in robust eggs. These direct-developing young avoid being tadpoles and emerge as fully fledged, if tiny, versions of their parents.

The new species have a variety of remarkable body forms, said Christopher J. Schneider, a biologist at Boston University. These species run the gamut from tiny leaf-litter dwellers to large tree-living types. Some live on rocks and have leg fringes and markings that help disguise them as clumps of moss, he said.

Striking finds

They found that many species known from 19th Century museum collections had seemed to have vanished.

The frogs discovered in the census fit into two groups. One, comprising just five species, lay their eggs in foam nests in leaves, rocks or braches just above the water.

But most of the newfound frogs are "direct developers", which hatch as tiny adults, missing out the tadpole phase.

Discussing the disappearance of old, known species, Madhava Meegaskumbura said: "Given that the island has lost more than 95% of its rainforest habitat, this is hardly unexpected.

"Still, the persistence of so many species is striking, and may be attributable to a combination of terrestrial eggs, direct-developing embryos, and high fecundity."

Global Free Fall

The discovery is good news considering the recently documented declines in amphibian numbers worldwide. "The discovery of these species is just an indication that we are losing some of the world's most important resources before we even know what those resources really are," said John W. Wilkinson, International Coordinator for the Declining Amphibian Populations Task Force at the Open University in Milton Keynes, England.

Around 5,000 amphibian species, including frogs, toads, newts, and salamanders are thought to exist today. These often semi-aquatic animals live in environments ranging from wetlands and forests to savannas and deserts.

Since the 1950s many species of amphibians have experienced plummeting numbers associated with habitat loss and other adverse human activities. However, since the late 1980s biologists began reporting an escalation in these declines worldwide—often with no clear cause, and even severely affecting species in otherwise pristine habitats such as national parks and nature reserves.

Scientists have been at a loss to find a single factor responsible for the declines that have caused the extinction of many species. Possible causes include pollutants such as pesticides, diseases such as fungal infections, climate change, and more ultraviolet radiation due to thinning ozone layers.

Declining amphibian populations are a concern, said Wilkinson, because they indicate general environmental degradation—with implications for the health of other animals, humans included—and because amphibian species, like vanishing rain-forest plants, are a potential source of new drugs. "Many frogs produce chemicals [and poisons through their skin] which could have huge applications in healthcare and medical treatment," he said.

Specimens of the newly discovered species were first collected in 1993 when Rohan Pethiyagoda, founder of Sri Lanka's Wildlife Heritage Trust based in Columbo, arranged to survey animal biodiversity in the nation's surviving rain-forest patches.

The island has lost 95 percent of the rain forests it once had, with remaining patches covering around 750 square kilometers (290 square miles)—less than 2 percent of the island. Many of the forests were cleared during the British colonial period, when the island was known as Ceylon, to make way for rubber, coffee, and tea plantations.

Remarkable Discovery

Pethiyagoda and his team collected over 1,000 frog specimens at 300 sites during the course of their extensive survey. When they attempted to identify the species they had collected they ran into considerable difficulty matching the animals to Sri Lanka's known frogs, said Schneider. International experts later confirmed that the researchers had turned up many previously undescribed species, said Schneider.

Subsequent work comparing the relationships among the species with the use of physical appearance, ecological similarity, frog vocalizations, and genetics helped confirm the novel nature of the animals. Pethiyagoda, and his team also compared the animals to Sri Lankan frog specimens in museums worldwide, to ensure none of the species had been previously described. Pethiyagoda, Schneider and their colleagues detail the discovery in the October 11 issue of the journal Science.

The fragmented nature of Sri lanka's rain forests, which are separated by grassland in some places, may have contributed to the large number of species, said Wilkinson. As direct-developing frogs are effectively stranded in habitats which have high humidity, the animals may have been divided into distinct breeding groups that over time diverged into separate species.

This remarkable discovery could mean that there are other vertebrate species waiting to be found across the tropics, said Schneider. "No other tropical rain-forest region, apart from Australia, is likely to have been as thoroughly surveyed as the Sri Lankan rain forests," he said. "Therefore we expect that there is substantial unknown diversity in tropical regions worldwide."

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WWW Virtual Library - Sri Lanka