‘Hangry' Beetles: Reduced aggression in response to food deprivation in a system where males fight for mates

Aggression is a key behavior for acquiring resources necessary for survival and reproduction, but it is both energetically costly and risky. Theory predicts that aggression should reflect a balance between an individual’s resource-holding potential (RHP) and motivation, yet predicting aggression under conditions of resource scarcity is challenging. Nutritional status is particularly important, as food deprivation reduces RHP but may simultaneously increase motivation to fight. Here, we examined how the duration of food deprivation affects male–male aggression in the broad-horned flour beetle, Gnatocerus cornutus , a species where combat is primarily used to secure mating opportunities rather than food. We paired size-matched males that were either fed ad libitum or starved for up to 11 days and recorded their aggressive behaviors during 20-minute trials. Our results show that short-term food deprivation reduces aggression, consistent with reduced RHP. However, as the duration of food deprivation lengthened, aggression in starved males gradually increased, resembling the “hangry” response described in other animals. In contrast, aggression levels in fed males remained stable across time. Importantly, these patterns were not explained by differences in general activity levels. These findings highlight a dynamic interaction between RHP and motivation, showing that severe resource limitation can override poor condition to elevate aggression. This work contributes to understanding behavioral plasticity under resource scarcity and demonstrates that aggression responses to food deprivation are complex and context-dependent.