The relative importance of size and asymmetry in sexual selection

Developmental stability reflects the ability of individualsto cope with their environment during ontogeny given their geneticbackground. An inability to cope with environmental and geneticperturbations is reflected in elevated levels of fluctuatingasymmetry and other measures of developmental instability. Bothtrait size and symmetry have been implicated as playing an importantrole in sexual selection, although their relative importancehas never been assessed. We collected information on the relationshipbetween success in sexual competition and size and asymmetry,respectively, to assess the relative importance of these twofactors in sexual selection. Studies that allowed comparisonof the relationships for the same traits' size and symmetryand success in sexual competition constituted the data, whichtotaled 73 samples from 33 studies of 29 species. The averagesample-size weighted correlation coefficients between matingsuccess or attractiveness and size and asymmetry, respectively,were used as measures of effect size in a meta-anatysis. Analysiswas conducted on samples, studies, and species separately. Wefound evidence of an overall larger effect of symmetry at thespecies level of analysis, but similar effects at the sampleor study levels. The difference in effect size for charactersize and character symmetry was larger for secondary sexualcharacters than for ordinary morphological characters at thelevel of analysis of samples. The results lend support to theconclusion that symmetry plays an important general role insexual selection, especially symmetry of secondary sexual characters.