Damage from intraspecific combat is costly

Abstract

When individuals engage in fights with conspecifics over access to resources, injuries can occur. Most theoretical models suggest that the costs associated with these injuries should influence an individual’s decision to retreat from a fight. Thus, damage from intraspecific combat is frequently noted and quantified. However, the fitness-related costs associated with this damage are not. Quantifying the cost of fighting-related damage is important because most theoretical models assume that it is the cost associated with the damage (not the damage itself) that should influence an individual’s decision to retreat. Here, we quantified the cost of fighting-related injuries in the giant mesquite bug, Thasus neocalifornicus. We demonstrate that experimentally simulated fighting injuries result in metabolic costs and costs to flight performance. We also show that flight costs are more severe when the injuries are larger. Overall, our results provide empirical support for the fundamental assumption that damage acquired during intraspecific combat is costly.

Sexually selected weapons can wear out, decreasing their effectiveness in combat

“…Thus, males with dull weapons likely have a reduced ability to inflict injury (i.e. a fighting cost [39]) onto their rivals, potentially allowing the rivals to persist in fights for longer [35,36,53,54]. It could also be argued that males with dull weapons have a harder time landing strikes on their opponent, potentially because they are unable to reach their rivals [55].…”

“…None of the specimens collected early in their season (0/60) had fighting-related injures on their wings [39], suggesting that they had yet to start fighting over access to mates and resources. Thus, these early-season specimens should provide insights into the natural variation in spine sharpness that is present when excluding weapon wear.…”

“…Adults of this univoltine species generally begin to emerge in June or July, with the adult abundance notably declining in September. For this first objective, previously collected specimens that were acquired early in a season (June/July 2020; n = 60 [39]) and later in a season (August 2021; n = 60 [31]) were used. Two of the individuals collected late in their season were missing their right hind legs due to autotomy, a common occurrence in this clade [40,41].…”

Genetic correlation between aggressive signals and fighting

“…Many animals rely on aggression for access to desirable resources and mates. While such aggression has obvious potential fitness advantages, fighting may also have severe costs, which range from lost time and energy to wounding and death [1–3]. The vast majority of aggressive encounters, however, do not involve fighting.…”