Weapon asymmetry indicates fighting ability in an earwig

Morphologies that are conspicuously asymmetric are thought to serve an adaptive\ud function. For the most part, these asymmetries have not been examined with respect to\ud the function of the morphology as a weapon. Animal weapons are often used to defend\ud resources through contests and can signal quality to potential mates and rivals. In this\ud study we describe an unusual right-biased asymmetry in the forceps of male earwigs\ud Anisolabis maritima, and investigate the relative importance of forceps asymmetry and\ud curvature in contests between males over food. The ability to dominate contests with\ud other males translated into a tangible benefit, as winning earwigs fed longer on the\ud resource. We found that in contests between large males, small differences in pronotum\ud width were sufficient to influence the outcome of fights, with larger earwigs winning. In\ud contests between small males, individuals with more asymmetric forceps and a more\ud curved forceps won more fights. An experimental manipulation of forceps asymmetry\ud revealed that a correlate of forceps asymmetry, and not asymmetry per se, affected the\ud outcome of agonistic interaction