Sexual imprinting and optimal outbreeding

Abstract

WHEN Konrad Lorenz showed that early experiences can have a dramatic influence on the mating preferences of birds, he proposed that ‘sexual imprinting’, as the process came to be known in English, enables adults to recognise their own species¹. Subsequent experimental work^2,3 has, however, suggested that, although early experiences can indeed have long-lasting effects, a bird may also show a preference for members of its own species in the absence of experience with any of them except itself. The implication is that a bird may have a predisposing bias for its own species and sexual imprinting merely refines this bias in natural conditions. If birds are able to identify and mate with their own species without prior experience (and seeing or hearing themselves is irrelevant) what is the biological function of sexual imprinting? One possible answer is that sexual imprinting is required for recognition of close kin so that, by selecting mates that are slightly different, the animal is able to strike an optimal balance between inbreeding and outbreeding⁴. The prediction is that the strongest mating preference of a bird should be for something a little different (but not too different) from the object with which it had been imprinted. I report here that male Japanese quail (Coturnix coturnix japonica) mate with slightly unfamiliar females in preference to females to which they were exposed in early life, and that both types of female are preferred to those with a grossly unfamiliar type of plumage.