Novel cost of a sexually selected trait in the rubyspot damselfly Hetaerina americana: Conspicuousness to prey

Conspicuousness to predators frequently has been invoked as a cost of sexually selected traits, but conspicuousness to prey has not. We tested for the latter using rubyspot damselflies (Hetaerina americana) as the predator. Previous work on this species showed that the red spots on male wings are intrasexually selected and reduce survival. Since female wings lack red spots, we first compared male and female weight gain rates per unit hunting time. Females gained weight significantly faster than males in both mg per hour and relative to body weight. We then compared the weight gain rates of females painted with red wing spots to those of control females painted with clear ink or not manipulated. Controls gained weight significantly faster than red-painted females. Behavioral observations revealed that red females attempted to capture prey at normal rates and experienced normal rates of agonistic interference from conspecifics of both sexes. Nevertheless, red females captured fewer prey per minute and per capture attempt than did sham-manipulated and unmanipulated controls. We infer that the red spots reduced female weight gain rates by increasing their visibility to prey. Close similarity between male and red female weight gain rates relative to unmanipulated females suggests that red spots may also be a hunting handicap for males.