Global relationships amongst black-browed and grey-headed albatrosses: analysis of population structure using mitochondrial DNA and microsatellites

The population structure of black-browed (Thalassarche melanophris and T. i mpavida) and grey-headed (T. chrysostoma) albatrosses was examined using bo th mitochondrial DNA (mtDNA) and microsatellite analyses. mtDNA sequences f rom 73 black-browed and 50 grey-headed albatrosses were obtained from five island groups in the Southern Ocean. High levels of sequence divergence wer e found in both taxa (0.55-7.20% in black-browed albatrosses and 2.10-3.90% in grey-headed albatrosses). Black-browed albatrosses form three distinct groups: Falklands, Diego Ramirez/South Georgia/Kerguelen, and Campbell Isla nd (T. impavida). T. melanophris from Campbell Island contain birds from ea ch of the three groups, indicating high levels of mixture and hybridization . In contrast, grey-headed albatrosses form one globally panmictic populati on. Microsatellite analyses on a larger number of samples using seven highl y variable markers found similar population structure to the mtDNA analyses in both black-browed and grey-headed albatrosses. Differences in populatio n structure between these two very similar and closely related species coul d be the result of differences in foraging and dispersal patterns. Breeding black-browed albatrosses forage mainly over continental shelves and migrat e to similar areas when not breeding. Grey-headed albatrosses forage mainly at frontal systems, travelling widely across oceanic habitats outside the breeding season. Genetic analyses support the current classification of T. impavida as being distinct from T. melanophris, but would also suggest spli tting T. melanophris into two groups: Falkland Islands, and Diego Ramirez/S outh Georgia/Kerguelen.