Biogeographical barriers to dispersal and rare gene flow shape population genetic structure in red‐footed boobies ( Sula sula )

Abstract

Aim The ecological and biogeographical factors that influence population differentiation in seabirds are likely to be too complex and nuanced to be captured by many commonly held models of population differentiation. Pelagic seabirds exhibit high natal philopatry but can disperse long distances, potentially leading to long periods of genetic isolation with rare gene flow between isolated populations. Here, we assess levels of population genetic structure and gene flow in red-footed boobies (Sula sula) to test two hypotheses: (1) terrestrial and marine barriers to gene flow have caused population genetic differentiation among red-footed booby populations, and (2) despite high genetic differentiation among populations, rare gene flow still occurs among populations. Location Tropical oceans. Methods We genotyped 282 red-footed boobies at microsatellite, nuclear intron and mitochondrial markers. We applied basic tests of population differentiation, such as analysis of molecular variance, and applied modern statistical phylogeographical methods (e.g., structure, BayesAss) to investigate the history of gene flow. Results Red-footed boobies form four major genetic populations that correspond to oceanographic regions (Atlantic, Indian, Western+Central Pacific and eastern Pacific Oceans). However, gene flow has occurred recently among these populations. Further differentiation was found within ocean basins. Although the levels of gene flow within ocean basins are more difficult to assess, gene flow appears to have occurred between genetically differentiated Indian Ocean colonies. Main conclusions The population genetic structure of red-footed boobies has been driven primarily by major continental and marine barriers to gene flow that also drive differentiation in other pelagic seabirds (e.g., the Isthmus of Panama and eastern Pacific basin). However, dispersal across marine barriers (but not major continental barriers) appears to have been relatively common. We suggest that such patterns of long-term isolation and rare gene flow may be common to pelagic seabirds.