Background matching explains repeatable individual variation in the defence strategies of a stick insect

Abstract

Visually matching the background environment is an important means by which many animals avoid predation. Yet natural habitats are rarely uniform over space and time. A key question is whether prey behaviour depends on an individual’s perceived vulnerability. Using the crowned stick insect (Onchestus rentzi) as a model, we ask whether individuals’ willingness to take risks, and their decision to react or to remain motionless when facing a predator threat, is explained by their appearance matching with the background and/or variation in their life history traits. Over four consecutive weeks, we assayed individuals’ tendencies to take risks and exhibit defensive displays in response to predation risk. We also measured individuals’ body reflectance relative to their background (i.e. contrast), and traits related to life history that might influence risk-taking behaviours—including reproductive traits in both males and females. Individuals differed consistently from each other in their behaviour over time, with risk prone individuals engaging more in defensive displays than risk averse animals. Although we found no effects of body reflectance per se on individual variation in behaviour, we observed a strong positive correlation between defensive behaviours and reflectance relative to the background (i.e. contrast), revealing a functional link between behavioural variation and perceived vulnerability that is independent of life-history traits.