Genomic variation, population history and within-archipelago adaptation between island bird populations.

Claudia A Martin,David S Richardson,Brent C Emerson,Juan Carlos Illera,Lewis G Spurgin,Claire Armstrong

doi:10.1098/rsos.201146

Abstract

Oceanic island archipelagos provide excellent models to understand evolutionary processes. Colonization events and gene flow can interact with selection to shape genetic variation at different spatial scales. Landscape-scale variation in biotic and abiotic factors may drive fine-scale selection within islands, while long-term evolutionary processes may drive divergence between distantly related populations. Here, we examine patterns of population history and selection between recently diverged populations of the Berthelot's pipit (Anthus berthelotii), a passerine endemic to three North Atlantic archipelagos. First, we use demographic trees and f3 statistics to show that genome-wide divergence across the species range is largely shaped by colonization and bottlenecks, with evidence of very weak gene flow between populations. Then, using a genome scan approach, we identify signatures of divergent selection within archipelagos at single nucleotide polymorphisms (SNPs) in genes potentially associated with craniofacial development and DNA repair. We did not detect within-archipelago selection at the same SNPs as were detected previously at broader spatial scales between archipelagos, but did identify signatures of selection at loci associated with similar biological functions. These findings suggest that similar ecological factors may repeatedly drive selection between recently separated populations, as well as at broad spatial scales across varied landscapes.

Highlights

Characterizing evolution at the genetic level is fundamental to our understanding of how populations adapt in response to changing ecological pressures [1]
The ability of species to adapt depends upon the amount of genetic diversity within populations, which in turn depends upon mutational processes, past and present demography, and selection
The distinct geographical and ecological structure of individual islands, combined with the barrier to gene flow provided by the ocean, enables hierarchical population structure to develop over time, and for local adaptation to occur [14]

Summary

Introduction

Characterizing evolution at the genetic level is fundamental to our understanding of how populations adapt in response to changing ecological pressures [1]. For a comprehensive understanding of how natural selection shapes genetic variation, studies are required on a variety of species with differing (and known) demographic histories, and across populations which have faced a wide range of selection pressures [2,3]. [4,5]), but large-scale studies can be carried out in most non-model organisms, providing opportunities for novel insights into evolutionary dynamics in the wild (see [6,7,8]). [8,15]), island systems provide an excellent opportunity to tease apart the roles of selection, drift and gene flow in shaping patterns of genetic diversity in nature [16,17] When combined with the large-scale genomic marker sets that can be generated (e.g. [8,15]), island systems provide an excellent opportunity to tease apart the roles of selection, drift and gene flow in shaping patterns of genetic diversity in nature [16,17]

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Conclusion