Whole genome sequencing reveals evolutionary history of enigmatic seabird family | Else Mikkelsen

Full Title
Whole genome sequencing reveals the evolutionary history of an enigmatic seabird family
Abstract
The Stercorariidae (skuas and jaegers) are a family of pelagic seabirds that range across the oceans of the world and breed at high latitudes in the Arctic and Antarctic. The evolutionary relationships amongst this family have been controversial, and discordance between mitochondrial and morphological characters have led to the suggestion that one of the species — the Pomarine Jaeger (Stercorarius pomarinus) or the Great Skua (S. skua) — originated through hybridization between divergent lineages. To test for a hybrid origin of these species and to resolve the enigmatic skua phylogeny, we sequenced the whole genomes of all seven Stercorariid species. We used a multispecies coalescent framework to reconstruct the Stercorariid phylogeny and performed a series of genome-wide tests for introgression between lineages. We find that discordance between the mitochondrial and nuclear phylogeny of Stercorariidae is caused by introgression of the mitochondrial genome from S. pomarinus into S. skua, but that this introgression event is accompanied by very little nuclear introgression. We also document additional introgression events involving most members of Stercorariidae, including introgression between lineages that were approximately 3.6 million years diverged at the time of hybridization. In addition, we uncover an unexpected signature of shared ancestry between a species that breeds in the northern hemisphere and a species that breeds in the southern hemisphere, suggesting a complicated biogeographical history of the group involving multiple trans-equatorial dispersal events between the Arctic and Antarctic. While we find that hybrid speciation has not likely contributed to the radiation of this seabird family, introgression has been a widespread feature throughout the evolution of this group and may have provided an avenue for adaptive introgression of traits between lineages.