Expanded tibiae enhance male mating success in the damselfly Platycnemis phyllopoda

In insects, elaborate male secondary sexual traits have evolved through sexual selection driven by visual signals. In odonates, such displays typically feature wing pigmentation or flight behavior; however, investigations into non-wing morphological ornaments remain relatively rare. To address this gap, we investigated the damselfly Platycnemis phyllopoda, in which males possess conspicuously expanded, white mid and hind tibiae. Our findings revealed that males perform sequential courtship displays utilizing their UV-reflective tibiae. Field monitoring demonstrated that males with larger hind tibial areas achieved significantly higher mating success; however, they exhibited lower resighting frequencies and shorter observation spans, suggesting potential survival costs or increased dispersal. Combined with positive allometry, these results indicate that the expanded tibiae may function as sexually selected ornaments. Ultimately, opposing selection acting on these structures likely constrains their evolutionary exaggeration, highlighting the complex interplay of selections shaping tibial morphology in odonates.