Genetic diversity in a moulting colony of southern elephant seals in comparison with breeding colonies

Southern elephant seals Mirounga leonina migrate seasonally between pelagic foraging areas in the Southern Ocean and breeding and moulting sites on subantarctic islands. Here we characterized genetic diversity of the elephant seal moulting colony from King George Island (KGI), South Shetlands Archipelago, in comparison with breeding colonies described in earlier studies. Although KGI serves as a breeding site, the numbers of elephant seals are up to 3 times higher during the moulting season, suggesting post-breeding immigration from other sites, or that large numbers of individuals skip the breeding season every year. High haplotype diversity and a high percentage of shared haplotypes is consistent with the hypothesis of immigration from other South Atlantic colonies, which is also supported by satellite tracking data from earlier studies. Estimates of effective population size at both mtDNA and microsatellite loci were unexpectedly high compared with the census size of the KGI colony, suggesting that they were elevated due to the presence of immigrants. However, we detected few immigrants and no genetic structure in the KGI colony, which could result from the genetic similarity between KGI and other breeding colonies from the South Atlantic, but could also be an effect of an insufficient sampling scheme. These results show the need for genetic monitoring of southern elephant seal colonies throughout their annual cycle to better understand the range of their seasonal movements and patterns of gene flow. The southern elephant seal serves as a model to study links between spatio-temporal environmental variability, population dynamics, and individual movements, physiology and reproductive behavior. Understanding the patterns of dispersal and gene flow in this species is essential to adequately address these general questions.