Weapon morphology and performance predict fighting outcomes in the giant mesquite bug, Pachylis neocalifornicus

Many animals engage in direct competition with other members of their species over access to resources. Winning such contests often increases an individual's fitness. Thus, it is important to understand which factors determine contest outcomes. In weapon-bearing species, body size and weapon size have been reported to be important predictors of fighting success. However, it is unclear if one trait is a better predictor of success compared to the other. Additionally, there are mixed results as to whether performance measurements (e.g. force output of a weapon) are better predictors of fighting success than linear measurements (e.g. weapon size and body size). In this study, we randomly paired 124 Pachylis neocalifornicus (Insecta: Hemiptera: Coreidae) males in territorial interactions to investigate whether differences in body size, weapon size or weapon performance best predict fighting outcomes. We found that weapon size and weapon performance are better predictors of fighting outcomes than body size. However, we did not find clear evidence that linear measurements are better than performance measurements at predicting contest winners, as suggested in a recent meta-analysis. These results highlight the importance of weapon performance measurements and encourage future studies to continue investigating how non-size related traits (e.g. performance) influence contest outcomes.