Talk at CES on 17 November 2016 at 10:30 am titled "Islands within sky islands of Western Ghats revealed from genetic and song divergences" by Dr. Robin Vijayan from Indian Institute of Science Education & Research (IISER) Tirupati
I use island systems to study ecology and evolution of birds in natural landscapes. Mountaintop habitats, such as on sky islands in different parts of the world, also form islands for species adapted to these specific habitats. It is imaginable that on these sky islands, valleys interrupt species distributions and can lead to range fragmentation, differentiation, and ultimately speciation on an evolutionary time scale. However, there can often be a disconnect between processes at an evolutionary time compared to the contemporary. Many tropical habitats have faced high levels of anthropogenic deforestation resulting in habitat loss and fragmentation. Processes operating at this recent ecological timescale may lead to changes in gene flow patterns and bird song dialects as possible precursors to speciation.
There are very few systems that allow us to investigate both evolutionary and contemporary processes simultaneously. The Western Ghats Shola Sky Islands are one such system where deep, wide valleys (such as Palghat Gap) are known to cause genetic differentiation in varied taxa, while at a smaller scale almost 80% of the mountaintop landscape has been modified by humans.
This system allows us to ask if species adapted to such evolutionary patchiness are impacted by recent anthropogenic patchiness; and what the drivers of these different processes may be.
Across the larger landscape of the Western Ghats, I found a nested impact with the depth and width of valleys impacting species differently, possibly due to the interaction of topography and paleoclimate. This study led to the description of two new genera of birds, with endemic radiations of seven species.
At a localised spatial scale, population genetic data of one endemic passerine across the landscape revealed higher contemporary differentiation relative to historic differentiation in anthropogenic fragments, despite the species’ ability to historically traverse shallow valleys. Simulations confirm recent isolation in the anthropogenic fragments of Western Ghats. These fragments are thus akin to islands within natural islands of montane habitat.
Birdsong, analogous to human language, is a cultural trait that changes rapidly and can be transmitted horizontally, across generations. In some passerine species, songs could thus provide greater resolution of isolation. Analysis of song data at a similar scale (to genetic data) reveals that songs have also changed rapidly in this system. Changes in spectral traits appear to correlate with recent anthropogenic isolation while syntax changes correlate with historic isolation.
I plan to conduct further research, hoping to expand to other landscapes, examining underlying causes for the emergent patterns that I have discovered in this landscape.