A Model for Male Mate Discrimination in Butterflies

Male butterflies can only perform a limited number of matings during their lifetime, due to the fact that they transfer a substantial amount of energy and non-renewable nutrients to females during each copulation. At least in some species the males seem to need a longer or shorter time to recover after each mating. This makes it advantageous to male butterflies to mate preferentially with large, newly eclosed females, which usually have the highest expected egg production. However, the cost of discrimination is that searching time will increase in relation to the proportion of females that will be refused. In this paper I present a model that investigates how these two consequences of mate discrimination influence the expected number of offspring a male will have. The model predicts no mate discrimination in sparse populations or when mortality rate is high. When the density of available females is high or mortality is low, there is an advantage to males preferring newly eclosed, large females. In species with long male recovery time or low male mating capacity, male discrimination among females should be more frequent.