You are what you eat: Diet-induced chemical crypsis in a coral-feeding reef fish

Abstract

The vastmajority of research into the mechanisms of camouflage has focused on forms that confound visual perception. However, many organisms primarily interact with their surroundings using chemosensory systems and may have evolved mechanisms to ‘blend in’ with chemical components of their habitat. One potential mechanism is ‘chemical crypsis’ via the sequestration of dietary elements, causing a consumer’s odour to chemically match that of its prey. Here,we test the potential for chemical crypsis in the coral-feeding filefish, Oxymonacanthus longirostris, by examining olfactory discrimination in obligate coraldwelling crabs and a predatory cod. The crabs, which inhabit the corals consumed by O. longirostris, were used as a bioassay to determine the effect of coral diet on fish odour. Crabs preferred the odour of filefish fed their preferred coral over the odour of filefish fed a non-preferred coral, suggesting coralspecific dietary elements that influence odour are sequestered. Crabs also exhibited a similar preference for the odour of filefish fed their preferred coral and odour directly fromthat coral, suggesting a close chemicalmatch. In behavioural trials, predatory codwere less attracted to filefish odour when presented alongside the coral it had been fed on, suggesting diet can reduce detectability. This is, we believe, the first evidence of diet-induced chemical crypsis in a vertebrate.