How important are direct fitness benefits of sexual selection?

Females may choose mates based on the expression of secondary sexual charac ters that signal direct, material fitness benefits or indirect, genetic fit ness benefits. Genetic benefits are acquired in the generation subsequent t o that in which mate choice is performed, and the maintenance of genetic va riation in viability has been considered a theoretical problem. Consequentl y, the magnitude of indirect benefits has traditionally been considered to be small. Direct fitness benefits can be maintained without consideration o f mechanisms sustaining genetic variability, and they have thus been equate d with the default benefits acquired by choosy females. There is, however, still debate as to whether or not males should honestly advertise direct be nefits such as their willingness to invest in parental care. We use meta-an alysis to estimate the magnitude of direct fitness benefits in terms of fer tility, fecundity and two measures of paternal care (feeding rate in birds, hatching rate in male guarding ectotherms) based on an extensive literatur e survey. The mean coefficients of determination weighted by sample size we re 6.3%, 2.3%, 1.3% and 23.6%, respectively. This compares to a mean weight ed coefficient of determination of 1.5% for genetic viability benefits in s tudies of sexual selection. Thus, for several fitness components, direct be nefits are only slightly more important than indirect ones arising from fem ale choice. Hatching rate in mate guarding ectotherms was by far the most i mportant direct fitness component, explaining almost a quarter of the varia nce. Our analysis also shows that mate sexual advertisements do not always reliably signal direct fitness benefits.