Exploring the effects of patchiness and fragmentation: genetic connectivity of a sky island bird in the Western Ghats
National Centre For Biological ScienceAuthors
Pooja Gupta, V.V. Robin, Uma Ramakrishnan
Habitat fragmentation is known to affect species in various ways, from limiting gene flow to extinction. Species on mountain tops, sky islands, would be further impacted due to their naturally patchy distribution. The sky islands of the Western Ghats, a continuous chain of mountains, is further fragmented due to large scale anthropogenic impacts. We examined the historic and contemporary geneflow of an endemic, threatened bird across its entire distribution.
We captured 219 individuals using mistnets and collected blood sample from Shortwings at nine locations(Fig A) and 15 microsatellite loci were amplified. Pairwise population differences were calculated using ARLEQUIN. We performed the hierarchical analysis of genetic structure to estimate the number of population clusters using STRUCTURE. We estimated recent (BayesAss) and historic (IMa2) migration both across mountains and across deforested landscapes.
Genetic structure analysis reveals three distinct populations across major biogeographic divides (Fig C). Each population shows low FST indicating the presence of gene flow and migration within the landscape. We detected recent movement of Shortwings within each population both across small sub-populations on isolated mountains (Fig B) and across sub-populations separated by anthropogenic fragmentation (GR,MN,KD,HW).
This first genetic connectivity study, across its entire distribution, clearly shows that sub-populations of a range-restricted species are connected despite a highly fragmented landscape. This may be because the species is using remnant forest patches within the production landscape to maintain connectivity, while it is also naturally used to patchy habitats (sky islands). There may be other adverse unexplored effects of fragmentation on the species’ biology.