Stress, developmental stability and sexual selection.
Sexual selection may give rise to increases in the general level of stress experienced by individuals, either because intense directional selection reduces the ability of individuals to control the stable development of their phenotype, or because extravagant secondary sexual characters on their own impose stress on their bearers. Sexual selection often acts against individuals with asymmetric or otherwise deviant phenotypes, particularly if such phenotypic deviance occurs in secondary sexual characters. A small number of studies suggests that such characters also are more susceptible to the disruptive effects of deviant environmental conditions than are ordinary morphological characters. Plants often show extensive phenotypic asymmetry, and pollinators avoid asymmetric flowers, either because they are generally less attractive or provide fewer pollinator rewards. Floral symmetry may give rise to sexual selection with direct or indirect fitness benefits, as in animals. Sexual selection in animals may result in selection for relatively larger male body size, an overall increase in body size of a lineage and an increased risk of extinction (Cope's rule). Reduced stress resistance associated with intense sexual selection may contribute to this trend.