Chilling Out or Heating Up? Thermal Plasticity of Seminal Fluid Proteins in Drosophila melanogaster.

Seminal fluid proteins (SFPs) play crucial roles in reproduction by shaping female post-mating physiology and behaviour, male sperm competition and sexual conflict between the sexes. However, we know little about how abiotic ecological factors regulate SFP expression and transfer. Here, we use quantitative proteomics in adult flies from a wild Drosophila melanogaster population to test how exposure to natural temperature variation (20°C, 24°C and 28°C) across two time scales (48 h and 13d), and under either no- or high-sperm competition risk, interact to shape SFP production and transfer. Short-term exposure to different temperatures resulted in lower SFP production and transfer at 24°C under no sperm competition risk, but no differences under high sperm competition risk. In contrast, both the production and transfer of SFPs were consistently reduced across sperm competition treatments after long-term (13d) exposure to low (20°C) and high (28°C) temperatures, including for key proteins in the sex peptide and ovulin networks that mediate female post-copulatory responses, sperm competition and sexual conflict. Our results show that natural temperature fluctuations can have a strong effect on SFP production and transfer, and thus on post-copulatory sexual selection dynamics.