![]() That’s really a pretty spectacular but yet unknown mechanism.ĭo cephalopods have a finite set of camouflage to draw on, or is there limitless variation? One of the vexing questions is: How do they control that? These animals don’t have binocular stereopsis like a human does-they have their eyes where your ears are, so they’re looking at the 3-D texture of the background with one eye, and then they reproduce that in their skin. That’s a very crude explanation of how it works, but that’s basically it. And when they contract the vertical ones and relax the concentric ones, the bump goes down, kinda like a balloon full of water-squeeze in the middle, something has to give elsewhere. The papillae in an octopus or a cuttlefish have concentric muscles and vertically oriented muscles, and when they squeeze the concentric ones, they relax the vertical ones, and the bump goes up. In the last few years, we’ve done work to figure out, anatomically, how they make those bumps, and it’s basically a muscular hydrostat. That 3-D texture is an extra attribute in camouflage that is very important for visual deception. Something that’s really unique about these animals that no other animal group has is the malleable 3-D texture of the skin. Cephalopods also have bumps in the skin called papillae. So, these three layers play into color and pattern. When a cephalopod contracts those muscles, the chromatophore opens into a disc of color. Radial muscles extend from each chromatophore “like the spokes of a bike, and they’re anchored out in the periphery,” says Hanlon. The top layer of skin in octopuses, squids, and cuttlefishes contains pigmented organs called chromatophores. A close-up of skin from the common cuttlefish (Sepia officinalis). But if you selectively expand pigments over some parts of the white base layer of leucophores and not others, then you create high contrast. The bottom layer doesn’t have any neurons it always looks the same all the time. Another set of neurons controls the change of iridescence. There’s one big nerve bundle that controls all three layers. The top layer of chromatophores is actually in three colors and three layers-yellow, red, and brown. So there are two mechanisms at play going on in the skin, and the combination of pigments and reflectors gives optical diversity. You have a top layer of chromatophores then you have a middle layer of iridophores, which produce the iridescent structural coloration and then you have a basement layer of leucophores. You’ve described cephalopod coloration as a three-layered system. Science Friday caught up with Hanlon to discuss what he’s learned so far about cephalopod camouflage, what burning questions still remain, and why the octopus footage featured in our SciFri video was particularly impressive. “Their primary source of defense is not being detected or recognized, and they’ve evolved this capability to a greater degree than other animals we know of.” At least 30 of his published studies have entailed experimental setups designed to tease apart how cephalopods change their color and body patterning “so rapidly, with such a sophisticated result.”Īnd Hanlon has another claim to fame: He’s the human star of one of Science Friday’s most popular videos, “ Where’s the Octopus?,” as well as its sequel, “ Where’s the Cuttlefish?” “Very few animals can change their camouflage, especially quickly,” he says. One feature that fascinates Hanlon is the rate at which these soft-bodied creatures can transform. Over the course of 35 years, his team has published more than 200 scientific papers on cephalopods, according to Hanlon. Hanlon is now a senior scientist at the Marine Biological Laboratory in Woods Hole, Massachusetts, where his lab primarily focuses on studying the mechanisms behind cephalopod camouflage and signaling, as well as the behavior and sensory experiences of these soft-bodied creatures. After about 20 minutes, “I was hooked for life,” he says. He patiently observed the creature, taking note of its changing camouflage as it slowly moved around to feed. “I couldn’t see what it was, but just kept staring in this depression of coral, and eventually saw an octopus sitting there.” “I sort of circled around, looking what on earth scared me so much,” he recalls. He was snorkeling in a shallow coral reef in Panama in 1968 when a blast of water swept across his stomach, startling him. Roger Hanlon’s infatuation with cephalopods began shortly after one scared the living daylights out of him. Can you spot it? Photo courtesy of Roger Hanlon A common octopus (Octopus vulgaris) in hiding.
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