Male mating success and paternity in the grey seal, Halichoerus grypus: a study using DNA fingerprinting

Grey seals breed colonially on remote coastal sites. Within the colony, males compete aggressively for access to the females. We compare field observations of breeding behaviour with paternity, as determined by DNA fingerprinting, in the breeding colony on the island of North Rona. In 89% of cases where paternity was assigned, the father was observed near the mother during her perioestrous period, although in some cases this was discovered retrospectively. However, the most likely candidate male, judged on the basis of behavioural criteria, was shown not to be the father in 36% of cases. Overall, DNA typed males were more dominant, maintained positions amongst the females for longer, and accounted for disproportionately more paternities than untyped males. However, the reproductive success of the typed males is not as great as their behavioural domination of copulatory opportunities would suggest. Possible contributory factors which could explain this include: (i) imprecision in the estimates of copulatory opportunity due to mobility of males or topographical influences on individual behaviour; and (ii) opportunities for subordinate males to copulate with receptive females, either sneakily within the colony or in the water.