A phylogenetic test of sympatric speciation in the Hydrobatinae (Aves: Procellariiformes)

Phylogenetic relationships among species can provide insight into how new species arise. For example, careful consideration of both the phylogenetic and geographic distributions of species in a group can reveal the geographic models of speciation within the group. One such model, sympatric speciation, may be more common than previously thought. The Hydrobatinae (Aves: Procellariformes) is a diverse subfamily of Northern Hemisphere storm-petrels for which the taxonomy is unclear. Previous studies showed that Hydrobates (formally Oceanodroma) castro breeding in the Azores during the cool season is sister species to H. monteiroi, a hot season breeder at the same locations, which suggests sympatric speciation by allochrony. To test whether other species within the subfamily arose via sympatric speciation by allochrony, we sequenced the cytochrome b gene and five nuclear introns to estimate a phylogenetic tree using multispecies coalescent methods, and to test whether species breeding in the same geographic area are monophyletic. We found that speciation within the Hydrobatinae appears to have followed several geographic modes of divergence. Sympatric seasonal species in Japan likely did not arise through sympatric speciation, but allochrony may have played a role in the divergence of H. matsudairae, a cool season breeder, and H. monorhis, a hot season breeder. No other potential cases of sympatric speciation were discovered within the subfamily. Despite breeding in the same geographic area, hydrobatine storm-petrels breeding in Baja California (H. microsoma and H. melania) are each sister to a species breeding off the coast of Peru (H. tethys and H. markhami, respectively). In fact, antitropical sister species appear to have diverged at multiple times, suggesting allochronic divergence might be common. In addition, allopatry has likely played a role in divergence of H. furcata, a north Pacific breeder, and H. pelagius, a north Atlantic breeder. This study demonstrates that a variety of mechanisms of divergence have played a role in generating the diversity of the Hydrobatinae and supports the current taxonomy of the subfamily.