The erroneous courtship hypothesis: do insects really engage in aerial wars of attrition? (#534)
Males of various flying insects perform conspicuous aerial interactions around their mating stations. The broadly accepted interpretation of their aerial interaction is a war of attrition, where two contestants perform costly displays, and the one that reaches its cost threshold earlier gives up. The particular requirement in this model is that some forces to match the intensity of display of the two contestants are necessary, and failure to enforce matching allows foul contestants that delay or stop their display to avoid paying contest costs. In addition, wars of attrition require flying insects to distinguish the sex of flying conspecifics, because their aerial interactions begin when intruders fly into the territory. We investigated past research on the behavior of territorial odonates and butterflies to clarify whether the two prerequisites of wars of attrition are fulfilled: 1) contestants can inflict substantial costs on non-displaying opponents, 2) contestants can discriminate the sex of flying conspecifics. In territorial odonates, we found an abundance of evidence that contests involve physical attack and that the ability of sexual discrimination is sufficient. Therefore, wars of attrition may occur in odonates. In territorial butterflies, however, we could not find any evidence that the two prerequisites are filled. Based on Lloyd Morgan’s Canon: the principle of parsimony in comparative psychology, males of territorial butterflies cannot distinguish the sex of flying conspecifics, and their aerial interactions are better interpreted as erroneous courtship between sexually active males. We constructed a model of male-male interactions of butterflies assuming that they maximize their fitness under the constraint that they cannot discriminate the sexes of flying conspecifics. We could interpret past research on butterfly contests by this erroneous courtship model. We think that the erroneous courtship model is far simpler than the war of attrition model, and that it is adequate for butterflies.