Female preferences for long tails constrained by species recognition in short-tailed red bishops

Sexual selection and species recognition both play important roles in mate choice. Typically, females use the relative expression of male sexual traits to select high-quality or attractive mates (sexual selection) of the same species (species recognition). However, when the variation in male trait expression of both conspecifics and heterospecifics overlaps, females potentially face a conflict between sexual selection and mate recognition. Among the highly polygynous and closely related African Euplectes species (widowbirds and bishops), females show a general and open-ended mate preference for extreme male tail length (even in relatively short-tailed species). To evaluate the relative strength and interaction of directional versus stabilizing selection pressures on tail length, we experimentally examined female mating preferences in the red bishop (Euplectes orix), a short-tailed (4 cm) species sympatric with longer tailed widowbirds (tails 7--50 cm). In standardized mate-choice experiments, females preferred naturally long-tailed males (5 cm), were indifferent to controls (4 cm), but discriminated against short-tailed (3 cm) and supernormal-tailed (8 cm) males. Although the naturally small variation in tail length (5%) is unlikely to function as a primary mate-choice cue, these results suggest a generalized female bias for longer tails (within the natural range). However, directional preferences for longer tails may be constrained by selection pressures to avoid heterospecific mating with the closely related and sympatric longer tailed widowbirds. Copyright 2008, Oxford University Press.