Good genes, oxidative stress and condition-dependent sexual signals

The immune and the detoxication systems of animals are characterized by all elic polymorphisms, which underlie individual differences in ability to com bat assaults from pathogens and toxic compounds. Previous studies have show n that females may improve offspring survival by selecting mates on the bas is of sexual ornaments and signals that honestly reveal health. In many cas es the expression of these ornaments appears to be particularly sensitive t o oxidative stress. Activated immune and detoxication systems often generat e oxidative stress by an extensive production of reactive metabolites and f ree radicals. Given that tolerance or resistance to toxic compounds and pat hogens can be inherited, female choice should promote the evolution of male ornaments that reliably reveal the status of the bearers' level of oxidati ve stress. Hence, oxidative stress may be one important agent linking the e xpression of sexual ornaments to genetic variation in fitness-related trait s, thus promoting the evolution of female mate choice and male sexual ornam entation, a controversial issue in evolutionary biology ever since Darwin.