Evolutionarily costly courtship displays in a wolf spider: a test of viability indicator theory

The costs of secondary sexual traits are crucial to our understanding of sexual selection. Although it is broadly accepted that sexual traits are indirectly or directly costly to express, few studies have quantified such costs. Thus, it is unclear if costs are evolutionarily meaningful and to what degree. Costs play a key role in viability indicator models, which assume that 1) the expression of sexual traits reduces the fitness of the trait bearer, 2) sexual trait expression is dependent on condition, and 3) the costs of sexual trait expression are borne differentially, that is, they are less for individuals in good condition. Using 2 syntopic species of wolf spiders, we addressed the importance of direct predation costs on the viability indicator mechanism. Pardosa milvina is a small wolf spider that has conspicuous male courtship behaviors in the form of front leg raises. Hogna helluo is a large species that preys on P. milvina. In laboratory experiments, we discovered that predation risk from H. helluo was higher for courting P. milvina males than noncourting males, male P. milvina manipulated to be in good condition courted at higher rates than males manipulated to be in poor condition, and males in good condition survived predation risk better than males in poor condition. Our study suggests that predation is a significant, evolutionary cost that can satisfy viability indicator mechanism assumptions. Copyright 2008, Oxford University Press.