Variation in male fertility in a polymorphic moth, Parasemia plantaginis

Abstract

The maintenance of multiple morphs in warning signals is enigmatic because directional selection through predator avoidance should lead to the rapid loss of such variation. Opposing natural and sexual selection is a good candidate driving the maintenance of multiple male morphs but it also includes another enigma: when warning signal efficiency differs between male morphs, why would females choose a phenotype with lower survival? We tested the hypothesis that indirect responses to selection on correlated characters through sexual selection may substantially shape the evolution of male coloration. If male phenotypes differ in their fertilization ability, female choice against the best surviving phenotype can evolve. The wood tiger moth, Parasemia plantaginis, has two coexisting male morphs in Europe. Previous studies have shown that yellow males are better defended against predators, but that white males have a higher mating success. We examined differences in fertility between white and yellow males in terms of sperm production, number of sperm transferred and rate of sperm replenishment, and association between these fertility traits, female mate choice and reproductive output. If white morphs have greater fertility than yellow males, then this could explain why females prefer to mate with white males. However, we did not find any difference between male colour morphs either in mating probability, fertility (i.e. sperm availability and sperm transferred) or reproductive success (i.e. number of eggs laid and hatching success). We discuss our results in relation to context-dependent mating success and maintenance of colour polymorphism within populations.