Has physical combat shaped the evolution of morphological and demographic traits in gladiator frogs (genus Boana)?

Abstract Since territorial behavior is one of the main forms of intrasexual competition, it has the potential to drive the evolution of traits that convey an advantage during contests, but also to constrain the evolution of other traits because of its energetic costs. However, most phylogenetic comparative studies have evaluated only whether territoriality has shaped the evolution of body size (i.e., the male combat hypothesis), coding this behavior as a binary variable. Here, we evaluate how the most aggressive component of territorial behavior (i.e., physical combat) has shaped the evolution of body size (snout–vent length), sexual size dimorphism, the relative size of the head, prepollical spine, and limbs, fighting experience (reproductive lifespan), and body growth rate, using gladiator frogs (genus Boana ) as a model system. Through phylogenetic generalized least squares regressions, we found that male snout–vent length was positively correlated with the percentage of individuals with dorsal scars and quantity of dorsal scars. Reproductive lifespan was positively correlated with quantity of dorsal scars and growth rate was positively correlated with the percentage of individuals with dorsal scars. Phylogenetic path analyses suggest that physical combat directly increases male snout–vent length and reproductive lifespan. Our results add further evidence for the importance of physical combat in the evolution of body size and reproductive lifespan. Conversely, the results suggest that physical combat may not drive the evolution of weapon size in territorial animals that do not use them in displays, but use them to inflict injuries by piercing while in direct body contact. Finally, we provide evidence of links of self-assessment models during physical contests and their frequency.