A foggy, froggy forest:
Sri Lanka’s frog radiation provides food for thought
Alvin POWELL
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, grey 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 the behaviour 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 behaviour 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.
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.”
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