Western Ghats helped evolution of two birds

The physical barriers posed by deep and wide valleys in the Western Ghats have helped evolution of two different species of song-birds on either side of the gap from a common ancestor over millions of years, Indian scientists have found.

One of the world’s biodiversity hot-spots, the Shola forests in the Western Ghats are marked with three such geographical gaps — the 40-km long Palghat Gap is the largest and oldest one followed by the Shenkottah Gap and the Chaliyar river valley.

Bangalore-based researchers have now spotted 10 examples of bird speciation – branches of two species from a common forefather – across the Palghat Gap. In addition, there are three similar examples in Shenkottah and one in Chaliyar river valley.

“The two birds with maximum impacts were Shortwing and Laughing Thrush that are separated for almost five million years in the Palghat Gap. On the either side of the gap, they now have different genetic make-up,” V V Robin, one of the members of the National Centre of Biological Sciences team that carried out the research, told Deccan Herald.

Speciation is a biological process by which new species come to the world. Though researchers in the past demonstrated how physical barriers like Panama canal that separates North and South America or Makassar Strait between Borneo and Sulawesi in Indonesia aided in speciation, there are not many studies in the Indian context.

The misty peaks of the Western Ghats, at 1,400 metres above sea level, are known as “sky islands” and home to a genetically diverse community of birds, with 23 species sharing the same habitat.

The habitation zones are characterised by grasslands in the mountain-tops, alternating with forests in the ridges and valleys in-between. The sky islands are spread over about 700 km, and are interrupted by deep valleys that fragment the habitat of these birds.

When the NCBS team set out to investigate genetic variation of all 23 species of songbirds in the Shola forests, they found 14 species with marked differences in their genetic make up because of the gaps. This suggests since the valley acted as a barrier, the birds on either side are genetically different and begin to diverge, potentially into new species.

“The extent of divergence is different for different species,” Robin said, “The deepest gaps impact more species than do shallower gaps. Correspondingly, divergences across deeper gaps are older than those across shallower gaps.” No change was noticed in nine bird species.

While the Western Ghats were formed at least 50 million years ago (Ma), the arrival of songbirds in the Ghats is dated to circa 34 Ma. The study appeared in the Proceedings of the Royal Society B on Wednesday.