Sex on the rocks: reproductive tactics and breeding success of South American fur seal males

Males of polygynous mammalian species may adopt different reproductive tactics to accomplish female fertilization, with dominant males often attaining a higher reproductive success than those adopting alternative breeding tactics. We worked on the largest breeding colony of the South American fur seal to determine its mating system and quantify the breeding success of male reproductive tactics using behavioral data and paternity assignment. We sampled ~50% of reproductive males during the 2010 breeding season and 85% of pups born during the following breeding season. Paternity analyses were made with 10 microsatellite markers, and 80% (n = 36) of the candidate fathers had at least 1 offspring (mean = 2.9, range = 0–13). Paternity was determined for 47% (n = 220) of pups at 80% and 95% confidence levels. We assessed the importance of different behavioral variables (tenure, copulation, and agonistic interactions) and reproductive tactics (territorial/satellite) in South American fur seal male breeding success using generalized linear models. We used regression trees to assess the homogeneity of breeding success within each reproductive tactic. The relatively high variance in South American fur seal male breeding success and the relatively high reproductive synchrony of breeding females and their distinctive pattern of space suggest that the mating system is consistent with a lek. We found that the territorial reproductive tactic was actually composed of 3 distinct categories and that a surprisingly high proportion of territorial males had a lower breeding success than the alternative satellite male reproductive tactics. This is the first study in otariids that has assessed the breeding success of male alternative reproductive tactics.