Perspectives in Ornithology Putting Sexual Traits into the Context of an Organism: a Life-history Perspective in Studies of Sexual Selection

BECAUSE SEXUAL TRAITS are often so striking, even bizarre, and seemingly different from other traits, researchers commonly study those traits in isolation from the rest of an organism, drawing evolutionary conclusions from the relation between the expression of a sexual trait and current reproductive success. However, because adaptation results from lifetime performance of an entire organism, it is not generally warranted to study the evolution of sexual displays in isolation from the performance of the entire organism and from the organism’s interactions with its ecological and social environment. Moreover, it is often assumed that the evolution of elaborate sexual displays is favored by mate preferences for further exaggeration. That is because the costs associated with the production and maintenance of a more exaggerated ornament are expected to facilitate the condition-dependence of ornament expression (Zahavi 1975, Andersson 1982, Grafen 1990). In turn, females mating with the most ornamented males are assumed to choose the best adapted mates that should sire the best adapted offspring (Andersson 1986, Pomiankowski 1988, Iwasa et al. 1991) and provide females with more phenotypic benefits (such as help with raising offspring; Hoelzer 1989, Price et al.