Genetic and Phenotypic Population Structure of an Endemic Mangrove Warbler Subspecies (Setophaga petechia xanthotera) along an Environmental Gradient in Costa Rica.

다국어 초록 (Multilingual Abstract)

A major goal of ecological and evolutionary biology is to identify the evolutionary responses of populations to novel or divergent habitats. Adaptation to local environmental conditions can influence evolutionary divergence along environmental gradients. Examining the association between phenotypic variation and population structure can be a powerful tool to infer the cause and effect between adaptive divergence and gene flow.In this study, we obtained samples from nine populations of Mangrove Warbler distributed along the precipitation gradient of the Pacific coast of Costa Rica to explore phenotypic and genetic divergence. Our main objectives were 1) determine if Mangrove Warbler populations are divergent in morphological traits along the environmental gradient 2) determine the balance between neutral genetic and phenotypic divergence to test for adaptation to local environments 3) investigated whether we could identify any population structure, given that FST is expected to be low between populations with no strong barriers 4) explored whether genetic variation could relate to variation in environmental variables among our populations 5) identify outlier loci to evaluate if there is population structure using region under diversify selection, and 6) identify candidate genes to determine if selection has acted on genes with functions related to the specific environmental variables along the gradient.Our results suggest that ecological divergence has occurred in this endemic subspecies, particularly in bill size. Our findings highlight the importance of understanding the selective factors when examining variation along environmental gradients.We did not find that our described habitat-specific phenotypic differentiation was corroborated by differentiation between populations at the genomic levels on Mangrove Warbler. Our results show that there is no genetic population structure between Mangrove Warbler populations along the gradient, and there is neither role of geographical distance nor environmental variables on genetic structuring. Our results add to several other studies that have identified likely local adaptation on phenotypic traits in the absence of genetic structuring.Finally, we detected associations between environmental variables and SNPs in genic regions. Some of the candidate genes that we found in Mangrove Warblers have been found in another species of birds that are adapted to deal with high salinity and water deprivation. This indicates an important role for osmoregulation in Mangrove warblers, and confirms that salt regulation and water availability may pose a particular challenge for a passerine species likely to ingest excess salt.