Sublethal Clothianidin Exposure Increases Trait Variation and Drives Sex-Specific Selection in the Water Strider...

Agricultural insecticides pose significant risks to non-target insects, extending beyond immediate mortality to sublethal effects that can alter evolutionary trajectories. While sublethal exposure may reduce average trait expression, it can also unmask hidden genetic variation, thereby increasing trait variance. Moreover, if coupled with sex-specific selection, such exposure could reshape sexual dimorphism. However, the role of sublethal insecticide exposure in driving these evolutionary dynamics remains poorly understood, particularly for semi-aquatic insects in agroecosystems. Here, we investigated how sublethal exposure to clothianidin, a widely used neonicotinoid, affects trait means, variance, and selection in male and female water striders (Gerris latiabdominis). We monitored lifespan and repeatedly measured body mass and activity of adults exposed to a sublethal concentration of clothianidin during their final nymphal stage, comparing with unexposed controls. Clothianidin exposure increased adult mortality risk and reduced body mass (male: -8.3%; female: -8.5%). Importantly, exposure substantially increased among-individual variance in body mass (male: 222%; female: 326%) and lifespan (male: 111%; female: 203%). Although these changes in means and variances were not statistically sex-specific, the increase in variance was more pronounced in females. In addition, positive viability selection on body mass was observed only in exposed females. These findings suggest that sublethal clothianidin exposure has the potential to influence the evolution of increased sexual dimorphism in body mass. Our results highlight the importance of considering insecticide effects on trait variance and selection-not merely trait means-to fully understand evolutionary changes in non-target populations. We suggest incorporating sublethal effects on semi-aquatic predatory insects into ecological risk assessments on agroecosystems.