Fine-scale population genetic structure and barriers to gene flow in a widespread seabird (Ardenna pacifica).

Pelagic seabirds are highly mobile, reducing opportunities for population isolation that might promote differentiation and speciation. At the same time, many seabirds are philopatric, and their tendency to return to their natal islands to breed might reduce gene flow sufficiently to permit local adaptation and differentiation. To test the net impact of these competing processes, estimates of differentiation and gene flow based on comprehensive geographical sampling are required. We leveraged diverse source material to achieve comprehensive geographical sampling in a widespread seabird, the Wedge-tailed Shearwater (Ardenna pacifica). Using data from sequence capture and high-throughput sequencing of 2402 loci containing 20 780 single nucleotide polymorphisms, we tested for population differentiation and gene flow among breeding areas. We found little evidence of deep divergences within A. pacifica but were able to resolve fine-scale differentiation across island groups. This differentiation was sufficient to assign individuals sampled away from breeding areas to their likely source populations. Estimated effective migration surfaces revealed reduced migration between the Indian Ocean and Pacific Ocean, presumably owing to land barriers, and across the equatorial Pacific Ocean, perhaps associated with differences in breeding schedule. Our results reveal that, despite their mobility, pelagic seabirds can exhibit fine-scale population differentiation and reduced gene flow among ocean basins. [ABSTRACT FROM AUTHOR]