Data from: 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 propose that ancestral anemonefishes had multiple stripes
that served for hiding/camouflage among the hosts’ long tentacles, while
increased specialisation towards fewer and more toxic hosts (with shorter
tentacles) led to the use of colouration as an aposematic signal. The
intriguing notion that an aposematic signal could advertise the defence of
another species may reflect the unique symbiotic relationship between
anemonefishes and their hosts.