Clownfish colours warn of danger – but it’s not the fish that predators are meant to fear.
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Nemo, the cartoon clownfish that lost its way, is not the most intimidating of characters. And yet new research has found clownfish colours evolved, in part, to instil fear into predators. But these are warning colours with a big difference.
Clownfish are famous for the intimate relationships they form with sea anemones. They seek protection among anemone tentacles, apparently immune to stings, and in return they aerate their hosts and fertilise them with nutrients. The 30-odd clownfish species specialise in partnering different species of anemone and come in a wide range of bright colours and white stripes.
“I’ve had the question about the function of their peculiar coloration in my head for a long while,” says Sami Merilaita of Finland’s University of Turku, who led the work. And now he has an answer. Working with Jennifer Kelley of The University of Western Australia, he has found a correlation between the colour patterns of the fish and the potency of venom deployed by their hosts. The more dangerous the anemone, the brighter the clownfish’s colours. The fish are palatable: it’s the host anemone that the fish are warning predators about. “We do not know of any other animal groups that might advertise a defence possessed by another species,” write the biologists.
Less venomous anemones host less colourful clownfish species sporting more white stripes, which Merilaita and Kelley believe is more to do with camouflage among the tentacles. But what of the classic Nemo clownfish look, with both bright colours and white stripes? Merilaita says it may be a compromise between camouflage and threat.
“The balance is between avoidance of detection by predators at long range and warning of the toxicity of the host at a closer range.” Nemo, it seems, would rather not be found. But should he be spotted, his message is clear:
“Get lost!” SB
FIND OUT MORE Journal of Evolutionary Biology: https://onlinelibrary.wiley.com/doi/abs/10.1111/jeb.13350
Clownfish Amphiprion ocellaris signal their host anemone’s danger. Inset, below: A. ephippium’s warning coloration is not compromised with camouflaging stripes.