Scary clowns: adaptive function of anemonefish coloration

Clownfishes, with their showy colouration, are well known for their symbiosis with sea anemones and for their hierarchical reproductive system, but the function of their colouration is unclear. We used a phylogeny of 27 clownfish species to test whether fish colouration: (1) serves a protective function that involves their anemone hosts, or (2) signals species identity in species with overlapping host ranges that can potentially share the same host. We tested for an association between fish colour pattern traits, host morphology and host toxicity and examined coloration in relation to host sharing and geographic proximity. Fish with fewer stripes occupied fewer anemone species, and hosts with shorter tentacles, than fish with multiple stripes. There was a negative relationship between anemone toxicity and tentacle length and these protective traits together were correlated with the evolution of stripes. Host sharing or range overlap was not associated with coloration divergence. We prop...