Contrasting patterns of population structure of Bulwer's petrel (Bulweria bulwerii) between oceans revealed by statistical phylogeography.

The patterns of population divergence of mid-latitude marine birds are impacted by only a few biogeographic barriers to dispersal and the effect of intrinsic factors, such as fidelity to natal colonies or wintering grounds, may become more conspicuous. Here we describe, for the first time, the phylogeographic patterns and historical demography of Bulwer's petrel Bulweria bulwerii and provide new insights regarding the drivers of species diversification in the marine environment. We sampled Bulwer's petrels from the main breeding colonies and used a statistical phylogeography approach based on surveying nuclear and mitochondrial loci (~ 9100 bp) to study its mechanisms of global diversification. We uncovered three highly differentiated groups including the Western Pacific, the Central Pacific and the Atlantic. The older divergence occurred within the Pacific Ocean, ca. 850,000 ya, and since then the W Pacific group has been evolving in isolation. Conversely, divergence between the Central Pacific and Atlantic populations occurred within the last 200,000 years. While the Isthmus of Panama is important in restricting gene flow between oceans in Bulwer's petrels, the deepest phylogeographic break is within the Pacific Ocean, where oceanographic barriers are key in driving and maintaining the remarkable structure found in this highly mobile seabird. This is in contrast with the Atlantic, where no structure was detected. Further data will provide insights regarding the extent of lineage divergence of Bulwer's petrels in the Western Pacific.