The influence of parental relatedness on reproductive success

TLDR

Studies of inbreeding depression have shown that parental similarity reduces fecundity, yet it is commonly assumed that adults from non‑closely related parents have comparable reproductive fitness, a premise that may overlook the influence of low‑quality inbred individuals. Across long‑finned pilot whales, grey seals, and wandering albatrosses, higher parental similarity consistently predicts lower genetic reproductive success, with no difference in effect across similarity levels, indicating a selective advantage for maximally dissimilar mates.

Abstract

The relationship between fitness and parental similarity has been dominated by studies of how inbreeding depression lowers fecundity in incestuous matings. A widespread implicit assumption is that adult fitness (reproduction) of individuals born to parents who are not unusually closely related is more or less equal. Examination of three long-lived vertebrates, the long-finned pilot whale, the grey seal and the wandering albatross reveals significant negative relationships between parental similarity and genetic estimates of reproductive success. This effect could, in principle, be driven by a small number of low quality, inbred individuals. However, when the data are partitioned into individuals with above average and below average parental similarity, we find no evidence that the slopes differ, suggesting that the effect is more or less similar across the full range of parental similarity values. Our results thus uncover a selective pressure that favours not only inbreeding avoidance, but also the selection of maximally dissimilar mates.