Phenotype-dependent mate choice in Propylea dissecta and its fitness consequences

Sexual selection in relation to male or female polymorphism has been investigated across the taxa. However, how polymorphism influences sexual selection has been investigated less in most organisms including ladybirds, with most studies in the latter on mating incidences in the field. Laboratory studies on morph-dependent sexual selection in ladybirds have assessed resultant reproductive performance but not consequences on offspring attributes, as well as maintenance of polymorphism. In the current study, we assessed mate choice in a dimorphic ladybird, Propylea dissecta, and its effects on fitness in terms of reproductive performance and offspring development. Females mate significantly more readily with typical darker morphs than with pale ones. Whether this is female choice or male–male competition requires more investigation. Better reproductive performance and increased offspring development and survival in monomorphic typical pairs indicated fitness benefits for individuals obtaining typical mates. Typical females had higher fecundity and their offspring developed faster and survived better than those of pale females. Females paired with typical males had higher egg hatchability than those paired with pale ones. Significantly more offspring of dimorphic pairs were of typical phenotypes whereas offspring of monomorphic pairs expressed the same phenotype as their parents. Female preference for typical males and the dominance of the typical trait likely explain the preponderance of typical morphs in the field.