Boosting Sri Lanka’s image as an amphibian hotspot, a group of Sri Lankan scientists have introduced a new genus of frogs that is endemic to the island. The new group is named Taruga meaning ‘tree climber’ in ancient Sinhala and Sanskrit.
This name is appropriate as the adults of these are tree-inhabiting frogs, rarely come to the ground, even laying their eggs on trees on overhanging foam nests.
Taruga is currently the only genus of endemic frogs among the tree-frogs (Rhacophoridae). Definition of a new genus is a rare occurrence, and for a vertebrate group, even rarer. The task of separating these species into a new genus is indeed complex and demanding.
The researchers have to analyse molecular DNA and morphological data such as the outward appearance as well as the form and structure of the internal parts like bones and organs of both adult frogs as well as tadpoles to distinguish this ancestry unique to Sri Lanka.
Dr.Madhava Meegaskumbura, the principal scientist behind this task, said, the research outcome published recently has been already updated in reputed amphibian journals further strengthening Sri Lanka as one of the world’s most important amphibian hotspots.
In science, a Genus is a classification used to group one or more species that has common characteristics which is the taxonomic rank just above that of the species name. For example, the four big cats – lion, tiger, jaguar and leopard are classified under the genus Panthera because of the common characteristics they share. Three of the endemic tree frogs that were previously called Polypedates (Whipping tree frogs) were re-classified under this new genus and have been given new scientific names -- Taruga eques, Taruga fastigo and Taruga longinasus.
The first part of a scientific name represents the genus, whereas the second part denotes the individual species name. However, a set of cone-like projections around the vent, a curved fold above the ear and a more pointed snout helped scientists to pull out three frogs to new genus Taruga. During a certain tadpole stage, the vent of Polypedates forms a tube between the left leg and tail, and in Taruga, there is only an opening between the leg and tail.
There are also several more features of the mouth cavity, such as the number of projections on the tongue and shape of the tongue that distinguishes Taruga from Polypedates.
These frogs also show some interesting characteristics with all frogs in this new genus building foam nests. The female is much larger than the male and carries him during amplexus. The female first selects a site usually a branch that hangs over water to make a bubble nest. Fluids secreted from the egg-carrying channel (termed the oviduct) are beaten up into a foamy mass by the female using her hind limbs.
The size of a foam nests can range from a ping-pong ball in some species, to a cricket ball in others. The eggs are laid within this foamy mass and the males fertilize the eggs. First the male and then the female leaves the nest, without providing any parental care to the nest. After several days, the eggs hatch and the tadpoles slip into the water from the overhanging foam nest to start their new life in the water.
Dr.Meegaskumbura said the tadpoles falling into the water at an advanced stage ensure a higher survivability from aquatic threats than if the eggs were laid in the water. The juvenile frogs that emerge from the water return to an arboreal life on the trees.
Rohan Pethiyagoda, another an expert taxonomist who is also involved in this research paper commented that the genus Taruga joins Nannophrys, Adenomus and Lankanectes as the fourth genus of frogs endemic to Sri Lanka.
These three species also show restricted distribution, where Taruga eques can be found 1000m above sea level (asl) in the central hills and the Knuckles range. Taruga longinasus: can be found below 600m in the wet-zone lowlands of Sri Lanka while Taruga fastigo is present only at 900m asl in the Rakwana mountains, recording the most restricted range.
Dr.Meegaskumbura acknowledges his graduate student, Gayan Bowatte who contributed to this work and other researchers who assisted them. He also acknowledges the support extended by the Department of Wildlife Conservation and Forest Department of Sri Lanka to carryout this work.
Amphibians the highest threatened
Around the world many species and populations are declining, but amphibians are the worst affected group among the vertebrates. Amphibians are sensitive to changes in the environment, so a small variation can be deadly for the frogs living in an affected area.
To add to the problem, many amphibians such as frogs of the genus Taruga are only found in restricted ranges; one species can only be found in a single forest patch, making them vulnerable to localized threats. Sri Lanka currently records 111 amphibians with 92 of them being endemic to Sri Lanka but the IUCN (World Conservation Union) has categorized 11 species of Sri Lankan amphibians as critically endangered and a further 36 as endangered. Some of these species are on the brink of extinction and require urgent conservation attention, or they could disappear even without our knowing about them. Sri Lanka has already lost 21 amphibians, in other words they have been categorized as being extinct. Deforestation, isolation of forests into smaller patches (fragmentation), disease, pollution, and climate change are triggering the extinction of amphibians.
“We have now realized that legal protection alone is insufficient to secure the future of these species. They need active conservation intervention, such as captive breeding and improved habitat security, in addition to regular monitoring of the existing populations so that any decline could be detected and addressed,” points out environmentalist Rohan Pethiyagoda, who discovered many frogs as part of his research few years ago.
Mr. Pethiyagoda added that at present, the only species on which the government spent money on conservation were elephants.
Yet, hundreds of Sri Lanka's endemic species and whole genera are threatened with extinction. If only a fraction of the funds spent on managing elephants were diverted to the conservation also of other threatened species, the outcome for the country's biodiversity would be much bette,” he said.
To make matters worse many of the protected areas in Sri Lanka are in the dry zone, whereas 80% of endemic fauna are found in wet zone rainforests, hill country cloud forests and related habitats.
Many of the threatened amphibians are in the wet zone and mountain areas where the habitats are shrinking faster than in the lowland dry zone (please see map). There are some critically endangered frogs currently surviving in a few areas outside protected areas, so a disturbance of these habitats would be deadly for these tiny amphibians.