The handicap hypothesis of sexual selection predicts that females prefer exaggerated male sexual ornaments because these traits signal male genetic quality. Males in good genetic condition are assumed to signal their quality through greater sexual trait size or more vigorous courtship display. Males in worse condition are unable to do this because they cannot bear the viability costs associated with such extravagance. Condition (or quality) is viewed as a trait closely related to viability, where higher values confer greater fitness. Models of the handicap hypothesis show that it can be a potent force in the coevolution of female preferences for exaggerated male sexual ornament (Pomiankowski, 1987; Grafen, 1990; Iwasa et al., 1991; Iwasa and Pomiankowski, 1994). Models show how the sexual ornament size and dependence on male quality respond to female preference. They predict that the handicap process leads to the evolution of heightened condition-dependent expression of the sexual traits. The samelogic applies when male quality varies due to environmental conditions and females gain directly (e.g. resources or parenting) from their mate choice, as we expect the cost of ornament exaggeration to have the same dependence on environmental quality asit does on genetic quality (Iwasa and Pomiankowski, 1999). So sexual trait condition dependence can evolve to signal both genetic and environmental qualities of males.
展开▼
