Introduction: What conservation problem or question does your study address?Knowing the mechanisms of the production of biodiversity is essential for its conservation. Island populations generally achieve endemicity through geographic barriers and such barriers between Sri Lanka and India have been porous. Climatic barrier therefore could play an important role. We tested whether the limited gene flow along the climatic gradient maintains the endemism in Dinopium woodpeckers through local adaptations in Sri Lanka.
Methods: What were the main research methods you used?We studied two subspecies; Dinopium benghalense psarodus (Red-backed woodpecker; endemic) and D. b. jaffnense (Golden-backed woodpecker), and their intermediate phenotypes. We sampled birds in 470 km transect spanning across the island from March to December 2013. Eight morphometric characters, 10 plumage characters and 50µl of blood were obtained from each bird. We measured the distance from mainland India to the capture location in two different methods; ‘geographic distance’ and to account for the climatic variability, ‘biogeographic distance’. Annual rainfall was used to determine the humidity and vegetation. We examined the variation of a nuclear non-coding region of Z chromosome and the mitochondrial CO1 using PCR-sequencing based genotyping. The patterns of co-variation between plumage, size and genotype were measured using principal components analyses (PCA).
Results: What are your most important results?A total of 70 individuals were sampled. The individuals captured from Jaffna had yellow plumage, while the wet zone had red plumage. The intermediate colour was found in the Northrn dryzone. The plumage characters showed a clear separation between three forms and a clinal variation along the biogeographic distance and rainfall. Morphometric characters did not show any variation. We found a gradual change in the frequency of alleles from North to South in the transect.
Discussion: What are your important discussion points and what is the relevance of your results to conservation (if any)?We found evidence for local adaptations resulting isolation by distance causing genetic and phenotypic divergence in Dinopium woodpeckers in Sri Lanka. The limited gene flow across climatic (rainfall) gradient likely played a role in generating endemicity in the subspecies level. The gene flow from mainland to the south is limited; therefore, the distance and climatic barriers limit the gene flow and insulate endemic taxa even in mobile groups like birds.