Fluctuating asymmetry in the redcollared widow : testing theories of sexual selection.

Abstract

Sexual selection is usually invoked to explain the evolution of elaborate epigamic characters in animals. However, the mechanism by which female choice operates is poorly understood, and it is not clear whether female choice is purely aesthetic or related to male genotypic quality. It has been suggested that Moller's fluctuating asymmetry (FA) hypothesis may resolve the 'arbitrary trait'-'good gene' debate. However, tests of this controversial hypothesis have yielded equivocal results. I examined the allometric patterns of FA in the redcollared widow in order to test the FA hypothesis. In addition, I documented intrapopulation variation in trait size to determine whether females could distinguish between males on the basis of ornament size and/or symmetry. Male tail length was found to be more variable in size than other traits, suggesting that sufficient variation exists in ornament size for females to distinguish between males on this basis. In addition, the prediction of the FA hypothesis that ornaments would display higher degrees of asymmetry than non-ornamental traits was supported. However, no significant linear or second-order polynomial relationship was found between trait size and asymmetry for tail, wing and tarsus length. Furthermore, neither tail length or symmetry was correlated with indices of body condition. Although this might suggest that the FA hypothesis is invalid, I argue that the assumptions of the hypothesis are too simplistic for it to hold true for all species without taking the basic biology of the species into account.