Males of the dragonfly Diastatops obscura fight according to predictions from game theory models

Abstract

Agonistic interactions between males for the ownership of mating territories are common among animal species. There are at least three theoretical models aimed to clarify the rules used by rivals to decide the contest winner: war of attrition model (WOA), sequential assessment model (SAM) and cumulative assessment model (CAM). However, few empirical investigations have simultaneously tested predictions from these three models, reducing our ability to infer each model's explanatory power. In this study, we used males of the dragonfly Diastatops obscura to identify traits that affect individual fighting ability (resource-holding potential, RHP) and to test predictions derived from WOA, SAM and CAM models. For this, we identified morphological and physiological male traits related to chances of victory, timed contests between males and evaluated the relationship between male traits, contest duration and performance of costly behaviours. Individual body mass represented the main trait affecting RHP. Contest duration decreased with increasing winner body mass and increased with increasing loser body mass, rejecting the WOA model. The probability of physical contact increased with decreasing mass differences between rivals. Additionally, when considering pairs of rivals that showed similar mass differences, contest duration was unrelated to loser body mass. Since fights can lead to physical contact, body mass may affect the capacity to inflict costs on the rivals. Also, the relationships between contest duration and RHP and between the probability of physical contact and RHP difference between rivals indicate that males perform mutual assessment of fighting ability, as presumed by SAM.