What drives patrolling behaviour by nasute termites? A model and an empirical assessment

Abstract

AbstractAnimals have evolved a number of antipredator strategies, which can reflect both intrinsic and extrinsic factors related to predation risk. In many termite species, a chemically armed soldier caste known as “nasute” engages in patrols upon breaching of foraging galleries, suggesting an adaptive response to imminent risk of mortality. However, the drivers of this collective behaviour are poorly understood. Here, I describe and test a qualitative model of patrolling behaviour upon gallery breaching by the arboreal termite Nasutitermes corniger (Termitidae: Nasutitermitinae). Patrolling behaviour is postulated to change throughout colony ontogeny, thus scaling with colony size. Further, this pattern is expected to be modulated by extrinsic cues for predation risk. Accordingly, patroller number increased with tree circumference at breast height, a surrogate for colony size. However, for any tree size, more soldiers engaged in patrols after repeated breaching, suggesting sensitization to structural damage. In parallel, patrolling rate (i.e., patroller number per time unit) was higher in smaller trees due to a disproportionate increase in patrol duration with patroller number. However, this response only occurred after repeated breaching; otherwise, patrolling rate was constant across tree sizes. Overall, patrolling behaviour by N. corniger seems to reflect intrinsic risks related to colony growth, adjusted by the extrinsic risk imposed by structural damage.