Contest dynamics and assessment strategies in combatant monkey beetles (Scarabaeidae: Hopliini)

Some of the most striking examples of intrasexual contest competition are to be found in the insects, whose weaponry and contest behaviors have become highly intricate and diverse. Game theory has been used as a basis to develop models of the competitive assessment strategies that may be used by males either to judge their probability of winning by comparing their own fighting ability to that of their opponents or to persist in contests for a period determined only by their own fighting ability. Conclusions from empirical studies about the means of assessment in their study systems have not, however, always been clear. In view of this, some authors have suggested that utilizing a broad suite of data concerning multiple facets of the study system may assist in gaining clearer insights into animal contests and assessment strategies. The present study integrates data on contest behavior, weapon morphology, residency effects, cost accumulation, and correlates of contest success to test game theory-informed models of competitive assessment strategies in the sexually dimorphic monkey beetle, Heterochelus chiragricus. We found that males of all sizes engaged aggressively in intrasexual contests for mating access to sedentary females, utilizing their hypertrophied hind legs as weapons. Contest outcome was determined by hind femur size and strongly influenced by residency effects. We found mixed support for both pure self-assessment and mutual assessment contest strategies. Such inconclusive findings are not uncommon in animal contest assessment studies, even when contest cost and resource holding power data are contextualized with behavioral and ecological data.