Impacts of ecology and behavior on Antarctic fur seal remating and relatedness

Abstract

Antarctic fur seals (Arctocephalus gazella) are polygynous and both sexes are typically faithful to a breeding site. These characteristics could promote remating among individuals over time, leading to increased relatedness levels and negatively affecting genetic diversity. To examine this issue, the reproductive output of 55 females was monitored annually for 12years and their pups were sampled (n=280) and genotyped using 17 microsatellite markers. A full likelihood pedigree inference method was used to confirm maternities inferred in the field and estimate the number of full sibling pups born across years. Relatedness coefficients were estimated for pairs of individuals in the pedigree and compared to simulated values for each relationship category. There were nine cases where a female mated with the same male twice and one case where a female mated with the same male three times over the study period. The observed relatedness coefficients estimated among the sampled pups matched the simulated distribution for half-siblings. In addition, no first order relatives were found among the fur seal mothers studied, nor did observed relatedness coefficient distributions differ significantly from simulated values. Together, these results suggest a low remating rate and a negligible effect of remating on pair-wise relatedness. Territorial male replacement over time as well as female small-scale movements, driven by suitable pupping habitat, likely contribute to the low remating frequency observed in Antarctic fur seals.