A life-history perspective on strategic mating effort in male scorpionflies

Abstract

In species with high male mating effort, there is a trade-off between mating effort spent in a current mating and resources left for future matings. Consequently, to maximize their reproductive success, males have to invest strategically, saving resources in matings with low reproductive gain for future, more valuable matings. However, as males age, the expected future reproductive success constantly declines. Thus, the importance of resource rationing may drastically change during a lifetime. Males of the scorpionfly Panorpa cognata offer females a costly nuptial gift before copulation, which functions as male mating effort. Resources for the production of these salivary masses are severely limited for males in poor condition. We found that males invested more in copulations with high-quality females than in copulations with low-quality females. However, males ceased to discriminate as they became older. Old males, with a relative small number of expected future matings, did not invest differentially in copulations with high- versus low-quality females. In copulations with low-quality females, males invested more in late than in initial matings, whereas in matings with high-quality females, time of mating had no influence on mating effort. These results imply that males adaptively change their resource allocation strategy during the course of the season. Initial matings seem to be characterized by male prudence; in later matings, males seem to adopt a more opportunistic mating strategy.