Non-visual crypsis: an updated review of current understanding

Crypsis, a form of camouflage wherein an organism conceals itself by hindering initial detection by a receiver, is widespread in the animal kingdom. Though crypsis has been the focus of much research, discussions of its function and evolution are mostly restricted to the visual domain. Crypsis is nevertheless a concept that can be usefully applied to non-visual sensory perception; and indeed, there have been major developments in the field of non-visual crypsis in the past decade. In this review, we first offer a definition of crypsis– one not restricted to the visual senses– before critically considering current avenues of study into non-visual crypsis and highlighting key, up-to-date findings. We examine which non-visual senses have the most convincing examples of crypsis, finding that auditory and olfactory crypsis have the most support, but this may be due to greater research efforts towards these senses rather than a natural dearth of examples in other senses. We also discuss the possibility of crypsis in underexplored senses, including mechanoreception, heat sensing, and touch. For all non-visual senses, we see great opportunities for future theoretical and empirical studies to explore the mechanism, ecological impact, and evolutionary and co-evolutionary implications of cryptic adaptations. We hope this review will provide an informative base for researchers, and encourage a shift away from restrictive, vision-centric definitions of crypsis.