Insulin-like peptide has antagonistic pleiotropic effects on male combat traits and survival traits in an armed beetle.

The expression of sexually selected traits, such as exaggerated weapons and ornaments, often entails trade-offs against life-history traits. While phenotypic trade-offs are well documented, the underlying molecular physiological mechanisms remain largely unexplored. In this study, we investigated the potential role of an insulin-like peptide, ILP2, in mediating the trade-off between sexually selected combat traits and survival traits in the broad-horned flour beetle, Gnatocerus cornutus. RNA interference (RNAi)-mediated knockdown (KD) of ILP2 during larval stages resulted in a reduction in the development of mandibular horns and overall body size. Interestingly, ILP2 KD males had increased lipid storage and enhanced starvation tolerance, indicating a shift in resource allocation from sexually selected traits to survival traits. Behaviorally, ILP2 KD males showed decreased locomotor activity and reduced aggression, leading to lower combat success. These findings suggest that ILP2 functions as a key mediator in the allocation of resources between combat and survival traits, highlighting its pleiotropic effects on morphology, metabolism and behavior. Our study provides novel insights into the molecular physiological mechanisms underlying life-history trade-offs associated with sexually selected traits.