The relative importance of size and asymmetry in sexual selection

Developmental stability reflects the ability of individuals to cope with th eir environment during ontogeny given their genetic background. An inabilit y to cope with environmental and genetic perturbations is reflected in elev ated levels of fluctuating asymmetry and other measures of developmental in stability. Both trait size and symmetry have been implicated as playing an important role in sexual selection, although their relative importance has never been assessed. We collected information on the relationship between s uccess in sexual competition and size and asymmetry, respectively, to asses s the relative importance of these two factors in sexual selection. Studies that allowed comparison of the relationships for the same traits' size and symmetry and success in sexual competition constituted the data, which tot aled 73 samples from 33 studies of 29 species. The average sample-size weig hted correlation coefficients between mating success or attractiveness and size and asymmetry, respectively, were used as measures of effect size in a meta-analysis. Analysis was conducted on samples, studies, and species sep arately. We found evidence of an overall larger effect of symmetry at the s pecies level of analysis, but similar effects at the sample or study levels . The difference in effect size for character size and character symmetry w as larger for secondary sexual characters than for ordinary morphological c haracters at the level of analysis of samples. The results lend support to the conclusion that symmetry plays an important general role in sexual sele ction, especially symmetry of secondary sexual characters.