Estimating the mating success of male butterflies in the field

Abstract

Sexual dimorphism in wing coloration is pervasive in butterflies and has been attributed to the process of sexual selection. However, this view has rarely been tested, partly owing to difficulties in estimating the mating success of males in the field. In the present study, we describe a method for assessing the mating success of male pipevine swallowtail (Battus philenor) butterflies, based on the appearance of their reproductive tracts. Laboratory experiments indicated that, in response to mating, components of the males' reproductive tracts become shorter, decrease in mass, and change in appearance, irrespective of age; and these changes persist for at least 2 days. Using these indicators of recent mating, we examined the reproductive tracts of 68 field-caught males and found that the color of the dorsal hindwing, a feature that females use in mate choice, was significantly greener in males that had recently mated than in males that had not.