Fellow’s focus is foggy, froggy forest

7 min read

Sri Lanka frog radiation provides food for thought

In the dark of the Sri Lankan cloud forest, the researchers’ only guide was the headlamps they used to light up the night, illuminating the cold, gray mist that drifted through the trees.

They looked carefully as they walked among the trunks, the beams from their headlamps casting left and right, up and down. They examined rocks and branches, leaf litter and shrubs, tree trunks, and leaves high in the canopy. By and by, they found one, then another — small tree frogs that froze in the light and went suddenly silent.

The frogs are a bit of living scientific gold. With amphibians declining around the world in what experts fear is a mass extinction crisis, these recently discovered tree frogs are strangely abundant and incredibly varied, an overlooked yet amazing display of biological diversity in a part of the world where British and Sri Lankan naturalists had worked for a century.

For the next two years, Sri Lankan biologist Madhava Meegaskumbura will be working at the Harvard University Center for the Environment to understand more about these frogs, studying how they evolved, why they go extinct, and how to prevent that fate for those that still exist.

“Sri Lanka is on the front lines of the global biodiversity crisis,” said Alexander Agassiz Professor of Zoology and Museum of Comparative Zoology Director James Hanken, with whom Meegaskumbura is working. “It is among the hottest of global biodiversity hotspots, even though less than 5 percent of original forest cover remains. This is true for the island’s amphibians, and especially tree frogs, which have undergone a unique and explosive adaptive radiation numbering hundreds of species.”

Meegaskumbura, a Ziff Environmental Fellow at the Center for the Environment, is planning a trip back to Sri Lanka in December to further his work in the field, which has already astonished amphibian experts around the world.

In 2002, Meegaskumbura, together with other Sri Lankan scientists and researchers from Boston University, told the world what they found: as many as 100 new species of tree frogs in the high cloud forests and lowland rainforests of Sri Lanka. The new frog species, most belonging to the genus Philautus, were found in remnant forests in a part of the island nation that had been largely deforested by British colonial planters to make room for plantations of tea, rubber, and cinchona, a tree whose bark is used to make the malaria treatment quinine.

“I was just completely blown away,” said Boston University associate professor of biology and herpetologist Christopher Schneider. “I was completely stunned by the finding. It was clear that there was this enormous radiation of frogs in Sri Lanka that nobody had recognized. … I don’t know when the last such discovery was made.”

The work was initially done under the auspices of a Sri Lankan nonprofit organization called the Wildlife Heritage Trust. Meegaskumbura joined the effort in 1998 and, together with Sri Lankan colleagues, helped confirm the unprecedented diversity using DNA techniques, examining museum specimens, observing behavior of living specimens brought back to the lab, and logging hours and hours in Sri Lanka’s high remnant forests.

“There’s obviously so much left to discover; that’s what’s exciting about Madhava’s discovery,” said Wildlife Heritage Trust founder Rohan Pethiyagoda.

In 1998, Meegaskumbura contacted Schneider, who became his doctoral adviser and helped guide several more years of work on the frogs. Meegaskumbura completed his doctoral degree at Boston University in 2007.

For two and a half years, Meegaskumbura, mainly together with colleague Kelum Manamendra-Arachchi, collected frogs and other relevant data in the forests. The work had to be done at night, when the frogs were active, and Meegaskumbura worked in the forests from 7 p.m. until 1 a.m. four or five nights a week, logging hundreds of hours.

Researchers exhaustively detailed what they found, recording frog calls and noting where each was found, what type of surface it was on, elevation, humidity, temperature, and other variables that, as they accumulated, painted a picture of the different species’ habits.

“The diversity of habitats you have to sample is amazing, places normally you wouldn’t expect frogs,” Meegaskumbura said.

Researchers also took tissue samples for DNA analysis and, in some cases, took the whole frog, either to be preserved as part of a research collection or to observe breeding behavior in a captive setting.

The forests were often difficult to traverse. The reason the forests survived is that they are perched on steep terrain unsuitable for farming. They held hidden dangers, some natural, some not. Leeches and snakes call the forests home and Meegaskumbura said he once had a notebook knocked out of his hand only to turn and see the open, white mouth of the pit viper draped in a nearby shrub. The snake had struck but hit only the book.

Researchers also had to be alert for manmade dangers. Hunters sometimes set up guns triggered by trip wires to catch wild pigs and other game. A wrong step could blow away a knee or a hip, depending on the height of the hunters’ quarry, Meegaskumbura said.

With the conflict between the government and Tamil separatists having ravaged Sri Lanka for the past 30 years, armed personnel could be another nighttime hazard. Meegaskumbura recalled one night when trucks full of men began shooting in the researchers’ direction from a road. He doesn’t know whether they were shooting live ammunition or not, whether they were hoping to hit something or just training, but he and his colleagues took cover behind the trees until the trucks passed, just to be sure.

The research so far has done more than bring to light the new frog species, Meegaskumbura said. The DNA work on the frogs has informed science’s understanding of their relationships to each other, reducing the number of main genera of Sri Lankan tree frogs from four to two, even though it increases the number of species within those groups. By searching museums for specimens of Sri Lankan frogs collected since the late 1800s, they have identified 19 species that are no longer found on the island and presumed to be extinct.

“These early reference collections that are now housed in reputed natural history museums worldwide were instrumental in highlighting the extinction of species in Sri Lanka,” Meegaskumbura said.

Their studies have shown that most of the frogs are terrestrial direct developers, Meegaskumbura said. Instead of laying eggs in the water, most of the new species lay eggs on land, skipping over the aquatic tadpole phase and hatching as juvenile frogs right from the eggs. Meegaskumbura said he believes this trait may be a key to their amazing diversity. Being able to have young independent of water, these frogs were able to venture far from streams and ponds and exploit a whole host of environmental niches unavailable to frogs whose reproductive needs tie them to water.

“It gives them ecological opportunity to diversify,” Meegaskumbura said.

Though the frogs don’t need water to breed, they still need moisture. The misty forests provide a damp environment for these direct breeders to lay eggs in. While one type of direct breeder buries their eggs in the forest floor, protecting them from fluctuations in temperature and humidity, another type sticks their eggs to foliage and is very vulnerable to drops in humidity.

That characteristic may make them sensitive to changes in the forest, Meegaksumbura said, either forest fragmentation that dries the interior out, or to a global warming that might raise temperatures and lower humidity.

“Global warming could have a devastating effect on these frogs. These are mountain isolates restricted to small areas,” Meegaskumbura said. “They could go extinct quite quickly.”

As part of his work at Harvard, Meegaskumbura wants to develop computer models that might help predict what kinds of changes the forests and frogs might face under different environmental circumstances, to help design conservation policies.

“The Environmental Fellows program was created to support the professional development of outstanding young scholars tackling complex environmental problems,” said Harvard University Center for the Environment Managing Director James Clem. “Madhava’s extraordinary field research as a graduate student has laid the foundation for exciting new insights to come as an Environmental Fellow.”