From mating to sperm storage: density-dependent plasticity in pre- and post-copulatory shared mating traits

Mating interactions depend on traits expressed jointly by males and females, yet the extent to which each sex controls variation in these shared mating traits remains unclear. Because the expression of such traits (like mating latency, copulation duration, and sperm transfer) depends on both partners, their evolution is constrained by intersexual correlations yet facilitated by behavioural plasticity that allows each sex to adjust trait expression across environments. In this study we investigated whether shared mating traits are determined by male or female control or if the observed outcomes result from interactions of the developmental environment of both partners. Drawing from the well-known mating system of the banded cricket, Gryllodes sigillatus, we used a fully factorial mating design using combinations of male and female partners reared at high or low density and tested how they shape shared pre- and post-copulatory traits. We found that female developmental density affected mating latency, with low-density females exhibiting longer latencies, suggesting female control and mate choice. In contrast, male developmental density affected sperm transfer and subsequent sperm storage, with males from high-density treatments transferring significantly more sperm consistent with adaptive ejaculate adjustment to sperm competition risk, as well as contributing to higher sperm storage in females. Copulation duration varied with female body mass but not density, indicating plastic responses to partner quality rather than social context. By partitioning environmental effects between the sexes, our study highlights how developmental context can be used to examine sex-specific contributions to shared mating traits.