Abstract
Two main hypotheses have been debated about the biogeography of the Southern Ocean: (1) theAntarctic Polar Front (APF), acting as a barrier between Antarctic and sub-Antarctic provinces, and (2)the Antarctic Circumpolar Current (ACC), promoting gene flow among sub-Antarctic areas. The Gentoopenguin is distributed throughout these two provinces, separated by the APF. We analyzed mtDNA(HVR1) and 12 microsatellite loci of 264 Gentoo penguins, Pygoscelis papua, from 12 colonies spanningfrom the Western Antarctic Peninsula and the South Shetland Islands (WAP) to the sub-AntarcticIslands (SAI). While low genetic structure was detected among WAP colonies (mtDNA UST = 0.037–0.133; microsatellite FST = 0.009–0.063), high differentiation was found between all SAI and WAP populations(mtDNA UST = 0.678–0.930; microsatellite FST = 0.110–0.290). These results suggest that contemporarydispersal around the Southern Ocean is very limited or absent. As predicted, the APF appears to bea significant biogeographical boundary for Gentoo penguin populations; however, the ACC does not promoteconnectivity in this species. Our data suggest demographic expansion in the WAP during the lastglacial maximum (LGM, about 20 kya), but stability in SAI. Phylogenetic analyses showed a deep divergencebetween populations from the WAP and those from the SAI. Therefore, taxonomy should be furtherrevised. The Crozet Islands resulted as a basal clade (3.57 Mya), followed by the Kerguelen Islands(2.32 Mya) as well as a more recent divergence between the Falkland/Malvinas Islands and the WAP(1.27 Mya). Historical isolation, local adaptation, and past climate scenarios of those EvolutionarilySignificant Units may have led to different potentials to respond to climate changes.