Exaggerated mandibles are correlated with enhanced foraging efficacy in male Auckland tree wē tā

Abstract

Sexual selection has driven the evolution of weaponry for males to fight rivals to gain access to females. Although weapons are predicted to increase males' reproductive success, they are also expected to incur costs and may impair functional activities, including foraging. Using feeding assays, we tested whether the enlarged mandibles of Auckland tree wē tā (Hemideina thoracica) impact feeding activity (the total volume of biomass consumed, bite rate, and number of foraging visits) and foraging behaviour (time spent moving, feeding, or stationary). We predicted that increased head capsule size in male wē tā would hinder their foraging efficacy. However, we found that wē tā with longer heads fed at a faster rate and spent less time foraging than wē tā with smaller heads, regardless of sex. Contrary to expectations that weapons impede functional activities, our results demonstrate that exaggerated traits can improve feeding performance and may offer benefits other than increased mating success.