Abstract:
Evaluating how populations are connected by migration is
important for understanding species resilience because gene
flow can facilitate recovery from demographic declines. We
therefore investigated the extent to which migration may
have contributed to the global recovery of the Antarctic fur
seal (Arctocephalus gazella), a circumpolar distributed marine mammal that was brought to the brink of extinction by the sealing industry in the eighteenth and
nineteenth centuries. It is widely believed that animals emigrating from South Georgia, where a
relict population escaped sealing, contributed to the re-establishment of formerly occupied
breeding colonies across the geographical range of the species. To investigate this, we interrogated
a genetic polymorphism (S291F) in the melanocortin 1 receptor gene, which is responsible for a
cream-coloured phenotype that is relatively abundant at South Georgia and which appears to have
recently spread to localities as far afield as Marion Island in the sub-Antarctic Indian Ocean. By
sequencing a short region of this gene in 1492 pups from eight breeding colonies, we showed that
S291F frequency rapidly declines with increasing geographical distance from South Georgia,
consistent with locally restricted gene flow from South Georgia mainly to the South Shetland
Islands and Bouvetøya. The S291F allele was not detected farther afield, suggesting that although
emigrants from South Georgia may have been locally important, they are unlikely to have played a
major role in the recovery of geographically more distant populations.
