The Telegraph
Monday , October 25 , 2010
Since 1st March, 1999
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When 1 bird became 2
Pic: Ramki Srinivasan

For the man on the street, discernible changes in the weather pattern are attributed to climate change. The impact of the latter — brought about primarily by the build-up of carbon dioxide in the atmosphere — however, stretches far beyond such shifts in our immediate surroundings.

Over the last few years, evolutionary biologists have stumbled upon evidence that reveals how climate shifts in the past disturbed the earth’s biodiversity. Many animal and plant species perished as a result of the onslaughts while others that were not so unlucky weathered the storm by enacting physical and genetic changes. Also, many new species emerged by branching off from existing species.

In March this year, a team of researchers from the University of Idaho and the State University of Washington found that polar bears, whose very survival was threatened, gained from a rapid accumulation of ice some 1,50,000 years ago. The study — based on genetic information garnered from the jawbone fossil of an ancient polar bear and compared with that of modern polar and brown bears — postulated that polar bears and brown bears split some 1,50,000 years ago.

Closer home, researchers in Bangalore recently unearthed genetic evidence of how two species of a small bird, found only in the Western Ghats — a mountainous region stretching over 1,600 km in southern and western India — emerged from a common ancestor because of climatic shifts. The study, by scientists at The National Centre for Biological Sciences (NCBS) and National Institute of Advanced Studies (NIAS), found that the white-bellied shortwing and Rufous-bellied shortwing — which live in and around Kodaikanal and Ooty in Tamil Nadu, respectively — split from a common ancestor some five million years ago.

Pic: Clement Francis

The Western Ghats are considered to be a biodiversity hotspot — a third of all Indian plant species, half the reptiles and 75 per cent of amphibians are found here. Forests covering these mountains harbour highly specialised species that are not found in lowland forests. These habitations are called sky islands, because of their isolation. Plants and animals in these pockets are virtually trapped, offering scientists a unique opportunity to learn about their origins.

Normally, when the climate changes, animal species try to follow the condition they have adapted to, moving around the landscape in an effort to stay in the same climatic space. However, some populations get left behind. These trapped populations have no choice but opt for physical or genetic changes or go extinct. “Species inhabiting high elevation regions are affected by climatic changes. As it gets warmer, they move higher up. And this makes them vulnerable to the threat of extinction,” says Uma Ramakrishnan of NCBS, a co-author of the study.

“The shortwing is a rarely sighted bird,” says V.V. Robin, the first author of the study which looks into the genetic make-up of the shortwing and the extent of relatedness among shortwing populations found in different sky islands. The work appeared recently in the PLoS ONE journal. Another scientist, who contributed to the study is Anindya Sinha of NIAS.

The main reason for the emergence of two different species of the bird was geographic isolation, coupled with climatic transition, says Ramakrishnan. There are several breaks in the stretch of the Western Ghats, the prominent ones in the studied area being the Palghat Gap and Shencottah Gap. These two low mountain passes offer rail and road connectivity between Kerala and Tamil Nadu.

Studies by the scientists showed that the shortwing populations on either side of the Palghat Gap — with the Nilgiris in the north and Anamalai Hills in the south — separated some five million years ago and split into two distinct species. While the white-bellied shortwing found in the Anamalai Hills has a white belly as the name suggests, the species in the Nilgiris has a reddish orange belly with a tiny white spot. Both the species were named by the late Salim Ali, the Indian ornithologist.

“We could spot some genetic changes in the shortwing populations across the Shencottah Gap as well, but they were minor ones,” says Robin. The population split across the Shencottah Gap occurred only about two million years ago.

The study provides an example of how animal species respond to changes in the climate of their immediate surroundings. “Such information will help predict how species may respond to climate shifts in future, allowing for more targeted conservation,” says Ramakrishnan.

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