The price of adulthood: ontogenetic patterns of mandibular wear in a drywood termite

Introduction In eusocial insects, the division of labor often entails significant mechanical costs for working individuals. In one-piece nesting termites, such as the Chilean endemic drywood termite, Neotermes chilensis , the colony's labor is performed by totipotent immatures that inhabit and consume structurally sound wood. This translates directly into severe mandibular wear. While the intense wood-processing activity of immatures has traditionally been viewed as an altruistic behavior that benefits the colony, recent evolutionary frameworks suggest it may represent a selfish developmental cost, the mechanical "price of adulthood", to fuel their own ontogeny into winged reproductives (alates). Conversely, alates, which can no longer molt to renew cuticular structures, must preserve their mandibles to excavate a nuptial chamber and found a new colony. Methods To investigate this, we quantified structural wear using a Mandibular Wear Index (MWI) and high-resolution scanning electron microscopy (SEM) across different developmental stages and sexes of N. chilensis (N = 147). To rule out size-related allometric artifacts, absolute mandibular dimensions were evaluated using an interactive Ordinary Least Squares (OLS) log -log model and estimated marginal means at a standardized common size (512.4 µm). Results Our results revealed no sexual dimorphism in wear but highly significant differences among castes that persisted independently of absolute mandibular size. Nymphs exhibited the most severe mandibular wear, consistent with their feeding activity to sustain energetic developmental demands. In stark contrast, swarmed alates possessed the sharpest, least worn mandibles. Primary reproductives and pseudergates displayed intermediate levels of wear. Discussion These findings reveal a caste-specific balance between mandibular wear in working immatures and preservation of mandibular structure in adult dispersers.