Behaviourally mediated camouflage in the furrowed crab (Xantho Hydrophilus)

Abstract

Camouflage is a classic adaptation used to conceal an individual and avoid detection or recognition by both predator and prey. Research on camouflage spans both artificial systems and real animals, often focussing on the types of camouflage that exist and how they work. It has long been known that many animals also use behaviour to facilitate camouflage, but many questions remain, and most studies are limited to certain taxa such as moths and birds. Here we use behavioural choice experiments, testing the responses of furrowed crabs (Xantho hydrophilus) to backgrounds differing in brightness, substrate grain size, and complexity to determine if individuals use behavioural choice to facilitate camouflage. Crabs preferentially chose backgrounds that were more similar in brightness to their own appearance but showed no preference for substrate size. In addition, crabs showed some tentative, but not statistically significant, preferences for complex, high contrast environments, providing some support for recent theories on the importance of environmental complexity in facilitating improved camouflage. We also found that furrowed crabs exhibit reduced intraspecific variation in carapace colour with age, which most likely reflects ontogenetic changes in coloration that are common in crabs or may be due to greater predation on less well-camouflaged individuals. There was also some evidence that the propensity to choose backgrounds increased with age. Thus, individuals can improve their camouflage through substrate choice, and this may improve with age. These findings provide insights into the camouflage behaviour and ecology of crabs and other animals, with implications for the tuning and efficacy of camouflage strategies.