Extreme polygyny among southern elephant seals on Sea Lion Island, Falkland Islands

Abstract

Elephant seals are known from long-term behavioral studies to be highly polygynous and to show high variance in reproductive success among males. However, genetic studies have determined that the level of polygyny varies between the closely related northern and southern elephant seals. In the present study, we investigate paternal success at the Sea Lion Island southern elephant seal colony in the Falkland Islands by using both behavioral measures and genetic markers. We find that the average success of harem holding males at Sea Lion Island is significantly higher than both the northern species and the nearby southern elephant seal population at Punta Delgada. We compare genetic paternity with various behavioral indices of male mating success, and we find that the behavioral measures provide a good estimate of the variance in male reproductive success. Only 28.2% of males achieved paternities, and among these, harem holders accounted for 89.6%. We discuss the implications of our results in the context of the demographic and physical environment. Specifically, a comparatively high variance in resource holding potential among males, differences in male social behavior, and a small tidal cycle limiting peripheral male access during female departure from the harem at this colony may be important factors leading to the comparatively high variance in male reproductive success at Sea Lion Island.