A case of the blues: linking guild coloration to service quality in a marine cleaning mutualism

Mutualisms are drivers of global biodiversity and are maintained via signaling between interacting parties. In marine cleaning mutualisms, where ‘cleaners' remove ectoparasites from ‘clients', guild coloration signals have evolved across dedicated cleaner species. Cleaner coloration is condition‐dependent. Color saturation could therefore be an honest signal for service quality. Using in situartificial cleaner experiments, standardized photography, and natural observations of the Caribbean neon goby Elacatinus lobeli , we show 1) potential clients interact significantly more with artificial cleaners that match the blue saturation of real cleaners; and 2) positive associations between E. lobeli blue saturation and cleaning frequency are dependent on client identity and ecology. We shed light on how color saturation can work as an honest signal for cleaning quality in the field exposed to diverse clients and discuss how it might affect client composition and resource partitioning.