Territorial clashes in the Neotropical butterfly Actinote pellenea (Acraeinae): do disputes differ when contests get physical?

Abstract

In many animals, males interact with or without physical contact to contest the possession of mating sites. The winner in such interactions often has larger body size and is the individual that previously occupied the territory (the resident). However, there is little consensus among studies on territorial insect species concerning which traits determine individual fighting ability, and why residency increases the chances of victory. We studied the butterfly Actinote pellenea to evaluate the hypothesis that stronger males are more likely to become residents, and that traits functionally related to behaviors adopted during contests should be important determinants of fighting ability. Males of A. pellenea grapple in the air and fall to the ground during combat. Therefore, we predicted that traits related to physical strength should be the most important determinants of the outcome of contests. To test our hypothesis, we observed fights between resident and intruder males, and fights in which both rivals were induced to behave as residents. We found that physical fighting was more likely when both rivals behave as residents. In addition, wing length and body mass were more closely related to contest success than age. Our results indicate that previous residency increases male motivation to fight, and that stronger individuals become residents. Although butterflies are considered weaponless, we suggest that traits important to contest resolution change according to behaviors adopted during disputes.