The genetic basis of speciation mechanisms in island birds

Abstract

Understanding the process of speciation, from incipient population divergence to the formation of reproductively isolated lineages, has been one the main goals of evolutionary biology. Recent advances in high-throughput DNA sequencing technologies have allowed studying the different stages of the speciation process in non-model organisms, providing affordable access to genome-wide data and information on neutral and adaptive population divergence and the genetic basis of relevant fitness traits. In order to contribute to the understanding of the speciation process, the aims of this thesis are: (1) to detect phenotypic divergence and the regions under selection that contribute to avian adaptation to insular environments by comparing the genomic landscapes of four different passerines that have colonized oceanic islands, including the red billed chough (Pyrrhocorax pyrrhocorax) and the common chaffinch (Fringilla coelebs) of La Palma in the Atlantic Ocean, and the dark-eyed junco (Junco hyemalis/insularis) and the house finch (Haemorhous mexicanus) of Guadalupe Island in the Pacific Ocean; (2) to study the mechanisms driving the diversification of the common chaffinch as it colonized different archipelagos in the Macaronesian region, and (3) to explore the genetic basis of local adaptation of the common chaffinch in La Palma, and its role in driving evolutionary divergence. The island-mainland four-species comparison shows that even though species have evolved parallel phenotypic changes upon island colonization that are consistent with the island rule, the genomic processes underlying these changes are lineage-specific. In Macaronesia, the common chaffinch has colonized the Atlantic archipelagos sequentially, starting from the continent to Azores, then Madeira and finally the Canary Islands, diverging in phenotype and genotype, and generating a species-level radiation. Within the island of La Palma, the common chaffinch have extremely reduced dispersal, and populations from two contrasting habitats show differences in phenotypic fitness traits and genomic structure associated with habitat variables, suggesting the role of local adaptation in the presence of gene flow and allowing the study of the divergence process at a very small spatial scale