Patterns of paternal relatedness in British grey seal colonies

Previous studies of breeding behaviour in the grey seal, Halichoerus grypus, have painted conflicting pictures. Behavioural observations suggest a classical polygynous system with a small number of dominant males fathering most of the offspring. However, genetic analysis suggests that many potential fathers spend little time ashore, that some pairs of seals show partner fidelity and that the dominant males are not as successful as their behaviour would suggest. Here we used paternal relatedness between pups with known mothers, sampled over an 11-year period, to show that behavioural dominance leading to enhanced fitness is a feature of only a handful of males located near the centre of the breeding colony. The vast majority of pups are fathered by any of a large number of males who all share approximately equal success, including virtually all those males who have previously escaped our best sampling efforts. As expected, the frequency of full-sibs is reduced in this longer time series relative to the original study. However, absolute estimates of the frequency of full-sibs seem to be confounded by a tendency for females who produce paternally unrelated pups to have conceived to males who are more genetically dissimilar from each other than expected by chance alone. Together, these elements of breeding behaviour would help to maintain maximum genetic diversity and to minimize the effects of inbreeding.