Antarctic fur seals, Arctocephalus gazella, were hunted to near-extinction in the early 1800's, but have recovered during the past 70 years to re-colonize most of their historical range. The large South Georgia (SG) fur seal population has been considered the main source of immigrants that re-colonized other areas, including Livingston Island (LI). Despite being one of the most exploited marine mammal species, clear evidence for a genetic bottleneck is lacking and instead, exceptionally high genetic diversity has been detected. Nevertheless, little is known about population-level patterns of genetic structure, or how this species' polygynous mating system may influence such patterns. This thesis fills some of this knowledge gap via extensive efforts in the field and in the laboratory, where over 1,000 individual samples were processed to obtain data on 17 highly polymorphic microsatellite markers; of these, 365 were also sequenced for mtDNA hypervariable region 1. The results of this work uncovered : (i) unexpected genetic differentiation between SG and LI indicating that LI was re-colonized by immigrants from one or more sources in addition to SG, (ii) remarkably high male reproductive success at a low- density LI colony during four breeding seasons, suggesting reduced competition among males at LI relative to the high -density colony of Bird Island (SG) (iii) a low percentage of rematings among individuals over the course of a decade, which was surprising considering the high level of breeding site fidelity and male reproductive skew found in this species, and (iv) one case of multiple-paternity in Antarctic fur seals among twins, showing that females may often escape control of territorial males within a breeding period. Not only do these findings provide unique insights into the remarkable re-colonization of Antarctic fur seals, but they also emphasize the importance of satellite populations for harboring genetic diversity through a period of profound anthropogenic disturbance. Additionally, by revealing complexities within male and female breeding behavior, this work advances our overall understanding of polygyny, providing insight into how it might function under different population densities and how individuals may interact over the course of their lives within this mating system

Many species have been heavily exploited by man leading to local extirpations, yet few studies have attempted to unravel subsequent recolonization histories. This has led to a significant gap in our knowledge of the long-term effects of exploitation on the amount and structure of contemporary genetic variation, with important implications for conservation. The Antarctic fur seal provides an interesting case in point, having been virtually exterminated in the nineteenth century but subsequently staged a dramatic recovery to recolonize much of its original range. Consequently, we evaluated the hypothesis that South Georgia (SG), where a few million seals currently breed, was the main source of immigrants to other locations including Livingston Island (LI), by genotyping 366 individuals from these two populations at 17 microsatellite loci and sequencing a 263 bp fragment of the mitochondrial hypervariable region 1. Contrary to expectations, we found highly significant genetic differences at both types of marker, with 51% of LI individuals carrying haplotypes that were not observed in 246 animals from SG. Moreover, the youngest of three sequentially founded colonies at LI showed greater similarity to SG at mitochondrial DNA than microsatellites, implying temporal and sex-specific variation in recolonization. Our findings emphasize the importance of relict populations and provide insights into the mechanisms by which severely depleted populations can recover while maintaining surprisingly high levels of genetic diversity.