UC San Diego

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