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Frog tales: Finding an alter ego a thousand kilometer away

Read time: 1 min
17 Sep 2020
Frog tales: Finding an alter ego a thousand kilometer away

Eastern Ghat Cricket Frog [Image credits: Prudhvi Raj]

Researchers discover a visibly different individual of the Eastern Ghats cricket frogs, in the Western Ghats

In the popular sci-fi TV series Doctor Who, the protagonist, Time Lord, finds his most profound emotion when he meets another Time Lord on his planetary trips to the other end of the galaxy. A team of herpetologists from India relieved that exhilarating experience when they found a frog on a rainy night in the Western Ghats. What's remarkable, you ask? Well, a relative of this frog, belonging to the same species, was first found about a thousand kilometers away, in the Eastern Ghats. This distance, although not on a galactic scale, is quite far for a frog to cover. The discovery is now raising exciting questions on how animals are classified and on our understanding of the Western Ghats’ biogeography.

Looking for frogs on a dark, rainy night, amidst the croaks, the leeches, and the slush in the Western Ghats is exhilarating. When Amit Hegde stumbled on a frog that resembled an Eastern Ghat cricket frog (Fejervarya kalinga), which is known to live only in the Eastern Ghats, he was bemused. This frog was similar to its Eastern Ghats counterpart, yet very different in some ways. Everything about it was bigger or longer. "Any classical taxonomist, who uses only bodily characters, would have considered these two frogs as different species", he says.

With other herpetologists from Karnataka University and Zoological Survey of India, Amit proceeded to look closely at his find. They carefully measured the frog with their Vernier calipers, from the snout to bottom and from tip to tip. They then plotted a graph and compared it with the measurements of the Eastern Ghats cricket frog. After comparing their DNA, they confirmed the two were the same species. They published their findings in the journal Zootaxa.

Western Ghat Cricket Frog [Image credits: Amit Hegde]

The researchers sequenced a gene called 16s RNA, which helps in identifying species-level differences. They compared it with the sequences of other species of Cricket frogs found in India. India has about 37 different species of cricket frogs. The analysis showed that the cricket frogs found in the Western and the Eastern Ghats were closely-related and, in fact, the same species. If you just saw them with your eyes, it may be hard to believe!

The researchers then constructed a phylogenetic tree — a schematic that traces the evolutionary relationships between species — based on the DNA sequences. "Phylogenetic studies suggested that the Western Ghats cricket frog could be a slightly divergent population of those found in the Eastern Ghats," says Amit, commenting on the findings. They found only a tiny (0.2%) difference between the genetic sequence of the two frogs, which suggests they are the same species.

In nature, animals of the same species, especially tiny amphibians like frogs, are found distributed around a small geographical region. But finding two specimens a thousand kilometers apart, in two different mountain ranges, has forced the researchers to rethink the distribution patterns of frogs. They now propose that the Eastern Ghats may be connecting the dispersal of the species to the Western Ghats and to the lush northeast parts of India.

But, why do the two specimens differ in their size? The researchers think it could be to adapt better to their surroundings, which differ in their altitude. "This might be a local adaptation or adaptation for two different geographical zones, or it could be adaptations due to rapid climate change," explains Amit. "Further studies on the genetics and natural history of these frogs are needed to ascertain this."

The current discovery shows how far and wide frogs can disperse and the role of climate in sculpting their bodily features. It also begs more studies on the genetic analysis of amphibians in India, new species of which are increasingly being discovered, to drive conservation policies to save them from extinction. 

This article has been run past the researchers, whose work is covered, to ensure accuracy.