Sexual Selection for Colour Phases in the Arctic Skua

Abstract

ACCORDING to Darwin¹, males who mate early in the breeding season gain a selective advantage. If the males of a species of bird, for example, establish their territories before the females come to breed, then the first females to arrive will mate either with males who have successfully maintained their territories or with those whom the females prefer. Darwin assumed that females who had had better nourishment before the beginning of the breeding season would breed earlier and rear more offspring, and, therefore, the males who mated first would also gain an advantage. Only some of the females may have particular mating preferences. A computer model, allowing for partial female mating preferences, showed that the preferred males can gain an advantage even when the earlier breeding pairs are not the fitter². The selection is frequency-dependent and can produce stable polymorphisms when balanced by natural selection.