JUANA SUMMERS, HOST:
And now clownfish, those popular splashes of color on coral reefs and aquariums and, of course, "Finding Nemo."
(SOUNDBITE OF FILM, "FINDING NEMO")
ALBERT BROOKS: (As Marlin) Are you woozy?
ALEXANDER GOULD: (As Nemo) No.
BROOKS: (As Marlin) How many stripes do I have?
GOULD: (As Nemo) I'm fine.
BROOKS: (As Marlin) Answer the stripe question.
GOULD: (As Nemo) Three.
BROOKS: (As Marlin) No. See, something's wrong with you. I have one, two, three. That's all I have? Oh. You're OK.
SUMMERS: Well, in some clownfish, those stripes disappear as they grow up, and new work suggests what might be triggering the costume change. Here is science reporter Ari Daniel.
ARI DANIEL, BYLINE: The adult tomato clownfish lives within anemones in the Western Pacific, and it's a striking little thing, says Laurie Mitchell, a marine biologist at the Okinawa Institute of Science and Technology.
LAURIE MITCHELL: Especially the females - they're kind of like a darker, tomato-like red color. The male is a lot smaller, and they tend to have a lighter complexion.
DANIEL: Now, what all adults do share is...
MITCHELL: A single white stripe down the head.
DANIEL: But young tomato clownfish just a couple weeks old have two to three white stripes. This is when they're settling onto an anemone for the first time and joining the pecking order of tomato clownfish already there.
MITCHELL: That's when they first have to interact with others of their own kind to form a functioning social hierarchy or group.
DANIEL: And avoid the alternative - being severely bitten or getting evicted from the anemone.
MITCHELL: That's certain death.
DANIEL: Young clownfish that do join an anemone successfully go on to lose all but one of their stripes, that white head bar.
MITCHELL: The timing of this loss - it's highly variable.
DANIEL: Happening between roughly 1 and 12 months of age, and Mitchell and his colleagues wanted to know what might be triggering that disappearance. The first step was to rear baby tomato clownfish in the lab.
MITCHELL: They're quite fragile as larvae. They're basically like human babies - you know, very demanding.
DANIEL: He then transferred the little guys to one of four experimental tanks. In two of them - one with just water and one with a plastic anemone - the young fish looked more or less the same 20 days later.
MITCHELL: Pretty much quite visible, solid white bars remain.
DANIEL: In the third tank with live anemone, the white stripes faded only slightly. It was in the fourth tank with a live anemone inhabited by a pair of adult clownfish where things were different. The little fish rapidly began losing all their stripes, except the head bar.
MITCHELL: And by the 38-day mark, they were almost completely not visible at all.
DANIEL: Mitchell also found a host of changes in gene expression, including those associated with cell death, affecting the cells producing the white coloration.
MITCHELL: These cells basically fragmenting and shriveling up and dying.
DANIEL: Here's what Mitchell thinks is going on. When young fish first arrive at an anemone, their small size and multiple stripes signal they're no threat to the pecking order.
MITCHELL: They're almost recluse. They're going between the tentacles, you know. But after that, there's no need to keep that multi-bar form because by the time it's gone, they've integrated into the hierarchy, and the function is fulfilled.
DANIEL: In some tomato clownfish in an unpredictable world appear to flexibly adjust when they lose their stripes to fit into a social group. The study's published in the journal, PLOS Biology. Theresa Rueger is a coral reef ecologist at Newcastle University who wasn't involved in the research.
THERESA RUEGER: This is an incredibly interesting paper, where you get the ecological side of the story, understanding how the fish live their lives, but you also get the mechanisms for us to understand how animals change these colors as they grow up.
DANIEL: Which Rueger says offers insights into biodiversity more broadly and how coloration is both influenced by the social environment and used as a signal within it. As for Laurie Mitchell, he's eager to see how this all plays out in the wild under natural conditions.
MITCHELL: They are such fascinating fish, you know? They have so many different unusual biological quirks.
DANIEL: Offering him plenty to learn inside a very colorful school. For NPR News, I'm Ari Daniel.
(SOUNDBITE OF KHRUANGBIN'S "MARIA TAMBIEN") Transcript provided by NPR, Copyright NPR.
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.
