Understanding the mechanisms of antitropical divergencein the seabird White-faced Storm-petrel (Procellariiformes:Pelagodroma marina) using a multilocus approach

Analytical methods that apply coalescent theory to multilocus data have improved infer-ences of demographic parameters that are critical to understanding population divergenceand speciation. In particular, at the early stages of speciation, it is important to implementmodels that accommodate conflicting gene trees, and benefit from the presence of sharedpolymorphisms. Here, we employ eleven nuclear loci and the mitochondrial control regionto investigate the phylogeography and historical demography of the pelagic seabirdWhite-faced Storm-petrel (Pelagodroma marina)bysamplingsubspeciesacrossitsanti-tropical distribution. Groups are all highly differentiated: global mitochondrial ΦST= 0.89(P < 0.01) and global nuclear ΦSTvaries between 0.22 and 0.83 (all P < 0.01). The completelineage sorting of the mitochondrial locus between hemispheres is corroborated by approx-imately half of the nuclear genealogies, suggesting a long-term antitropical divergence inisolation. Coalescent-based estimates of demographic parameters suggest that hemisphericdivergence of P. marina occurred approximately 840 000 ya (95% HPD 582 000–1 170 000),in the absence of gene flow, and divergence within the Southern Hemisphere occurred190000ya(95%HPD96000–600 000), both probably associated with the profound palaeo-oceanographic changes of the Pleistocene. A fledgling sampled in St Helena (tropicalSouth Atlantic) suggests recent colonization from the Northern Hemisphere. Despite thegreat potential for long-distance dispersal, P. marina antitropical groups have beenevolving as independent, allopatric lineages, and divergence is probably maintained byphilopatry coupled with asynchronous reproductive phenology and local adaptation.Fundação para a Ciência e Tecnologia (FCT