Johan Wallander

Genetic similarity between mates and extra-pair parentage in three species of shorebirds

Matings between close relatives often reduce the fitness of offspring, probably because homozygosity leads to the expression of recessive deleterious alleles. Studies of several animals have shown that reproductive success is lower when genetic similarity between parents is high, and that survival and other measures of fitness increase with individual levels of genetic diversity. These studies indicate that natural selection may favour the avoidance of matings with genetically similar individuals. But constraints on social mate choice, such as a lack of alternatives, can lead to pairing with genetically similar mates. In such cases, it has been suggested that females may seek extra-pair copulations with less related males, but the evidence is weak or lacking. Here we report a strong positive relationship between the genetic similarity of social pair members and the occurrence of extra-pair paternity and maternity (‘quasi-parasitism’) in three species of shorebirds. We propose that extra-pair parentage may represent adaptive behavioural strategies to avoid the negative effects of pairing with a genetically similar mate.

Animal behaviour: Relative size in the mating game

A common trend in size differences between males and females is a long-standing puzzle. A study of shorebirds shows that the type and strength of competition for mates may explain much of the pattern.

Evolutionary biology (communication arising): Why do birds engage in extra-pair copulation?

Griffith and Montgomerie question our finding that extra-pair parentage in shorebirds correlates with the genetic similarity of social mates, on the grounds that band-sharing coefficients (calculated by comparing bands on DNA fingerprints) are unreliable for determining the degree of genetic similarity between two individuals.

Why do birds engage in extra-pair copulation? Reply

Griffith and Montgomerie question our finding that extra-pair parentage in shorebirds correlates with the genetic similarity of social mates, on the grounds that band-sharing coefficients (calculated by comparing bands on DNA fingerprints) are unreliable for determining the degree of genetic similarity between two individuals.

Why do birds engage in extra-pair copulation?

Griffith and Montgomerie question our finding that extra-pair parentage in shorebirds correlates with the genetic similarity of social mates, on the grounds that band-sharing coefficients (calculated by comparing bands on DNA fingerprints) are unreliable for determining the degree of genetic similarity between two individuals.