Female preference for symmetrical vertical bars in male sailfin mollies.

Fluctuating asymmetry is defined as random deviation from perfect bilateral symmetry in otherwise symmetrical morphological traits and originates from developmental errors during ontogeny. It is thought to reflect the inability of a genotype to buffer itself effectively against environmental perturbations, thus providing an honest phenotypic indicator of genetic quality. It has been proposed that females use the degree of asymmetry in male ornaments to assess male quality in mate choice. We studied whether fluctuating asymmetry in vertical bars in the sailfin molly, Poecilia latipinna, is a criterion in female mate preference, as has been shown before in a swordtail, Xiphophorus cortezi. Using both live stimulus males and silicon models, we found that females have significant preferences both for bars per se and for males with symmetrical bars. The total number of bars and the degree of fluctuating asymmetry were negatively related so fluctuating asymmetry in bars may be an honest signal. This phenomenon may have influenced the evolution of the male courtship display in P. latipinna. Copyright 1998 The Association for the Study of Animal Behaviour.