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Clown­fish colours warn of dan­ger – but it’s not the fish that preda­tors are meant to fear.

BBC Wildlife Magazine - - Contents -

Per­se­cu­tion of birds of prey in Scot­land has fallen fol­low­ing new leg­is­la­tion

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.

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