Condition dependence of the multimodal courtship of a parasitoid wasp (Leptopilina heterotoma).

Abstract

Courtship displays often consist of more than 1 modality, despite additional costs associated with multiple modalities. Because courtship signals under strong sexual selection often show heightened condition dependence, they may convey information about mate quality. However, much of the research on condition dependence has focused on individual modalities. Theoretically, different modalities within 1 multimodal signal could show different degrees of condition dependence, depending on how strong the selection pressure is on each modality. Here, we investigate how male condition affects the multimodal courtship of the parasitoid wasp Leptopilina heterotoma. Specifically, we tested how 2 components of the multimodal courtship-a chemical signal (cuticular hydrocarbons, CHCs) and a vibratory signal (wing fanning)-are affected by age and nutritional state. We found that the 2 modalities responded differently to the male condition: Wing fanning was affected by both age and nutrition, whereas the chemical profile was only affected by age. In combination with previous studies, we conclude that wing fanning signals male quality and thus should be condition dependent, while the CHC profiles signal species identity and should remain stable. This further supports that L. heterotoma has a multimodal courtship display that conveys multiple messages. Additionally, we show that males increase their wing fanning frequency when mounted on the female. This behavioral adjustment during the courtship sequence is likely an energy-saving strategy, given the high energetic cost of wing fanning.