Study identifies distinct frog species not belonging to generic ‘hourglass’ classification

by Ifham Nizam

A study on the abnormalities and polymorphisms of amphibians found within and outside the Horton Plains National Park has identified a distinct frog species that does not belong to its generic “hourglass frog” classification.

The study was conducted by graduate research assistant Praneeth Silva of Sri Jayewardenepura University’s Department of Zoology under the supervision of Prof. W. A. D. Mahaulpatha, senior lecturer and head, Department of Zoology.

“Our study on amphibian abnormalities and causes found that Taruga eques species is faced with bigger threats in both localities in comparison to other amphibian species”, Silva told The Sunday Island.

Within and outside regions of the Sri Lankan Plains, habitat modifications due to human activities were the main threat on Taruga eques. The study also found that natural predators were the main cause for formation of amphibian abnormalities found within the Plains.

The study revealed a novel pattern polymorphism of Taruga eques in that a variety of the species without the hourglass was identified within and outside the Plains, indicating that the common name Taruga eques cannot be broadly classified as an “hour-glass frog”. At the end of the study, new six dorsal colour variations and five dorsal pigment patterns of Taruga eques could be newly introduced to the science.

Amphibian body colouration and pigment patterns play a vital role for their survival in the environment. Polymorp-hism (happening together in the same habitat of two or more distinct species results in rarest of them getting mutated to be like the main species) has probably led Taruga eques to be seen as hourglass tree frog though in reality the situation is likely to be rather different.

Silva said that a total of 694 amphibians belonging to four families and 11 species were recorded in five lentic water bodies which were studied. Five hundred and eleven (511) individuals were examined inside the Plains and 183 outside the region. Of the 511 individuals, only 4.5 percent of the amphibians had abnormalities. Of the 183 individuals examined outside the Plains, 80.87 percent had abnormalities.

Of the 511 inspected amphibians within the Plains, 0.59 percent suffered from ectromelia and four percent had cysts. Of the 183 amphibians examined outside the Plains, 80.33 percent had cysts and 0.55 percent had femoral projections. Cysts accounted for most of the abnormalities in both environments. Most of the infections (60 percent) recorded in the amphibians inside the Plains were mild. In contrast 77.55 percent of the infections recorded in the amphibians outside the Plains were moderate.

A research associate attached to the University of Indonesia Research Centre for Climate Change Thasun Amarasinghe said that not only hourglass tree frogs but almost all amphibians in Sri Lanka are under threat.

“They are called hourglass tree frogs as they have a colour pattern like an hour glass mark on their dorsum (back). They are highland species, and are very sensitive to temperature and humidity so in addition to habitat loss and forest fragmentation, there will be a future threat to them due to climate change”, he warned.

The major conclusion of the study was the natural selection results in the ‘polymorphisms’ to face the threat of predation. Moreover, colour and pattern polymorphisms manifest due to strong selection by visually oriented predators and the polymorphisms are highly valuable for the species to ensure their survival in the environment, while helping them to avoid abnormalities.

(Pix courtesy Praneeth Silva)