Invisible Shrimp: Exercise Disrupts Transparent Camouflage

Marine creatures such as the Pederson's cleaner shrimp use a sort of transparent camouflage that makes their bodies nearly see-through and invisible to predators. Ironically enough, however, any sort of "exercise" -- or rather three quick tail flips -- used by these shrimp to scurry away from predators disrupts their sneaky camouflage, turning their bodies from clear to opaque or cloudy. In the latest study from Duke University, researchers investigate why the shrimp have clear bodies to begin with and what about exercise-like movements causes them to shed their invisibility cloaks.

Under normal conditions, the body of a Pederson's cleaner shrimp (Ancylomenes pedersoni) is clear enough for them to easily blend in with any color of coral reef around them. For an eye to see an object, light must bounce off the object and hit the photoreceptors of the eye, researchers explained. So to be transparent means animals essentially allow light to pass through their bodies, rather than scatter, according to a news release. (Scroll to read more...)

Unlike most see-through creatures that float about in the ocean, embracing a blob-like existence, cleaner shrimp work hard for a living as fish groomers, thus forming symbiotic relationships with a few neighboring reef species, such as anemones, researchers say. Therefore many species of cleaner shrimp have evolved a body color pattern that matches that of their host. But Pederson's cleaner shrimp are the oddballs in the family: They have bodies that are almost completely see-through -- except for when they wiggle their tails.

For their study, Ph.D. student Laura Bagge of Duke University and a team of researchers investigate how such movement turns these clear shrimp cloudy. Ultimately they found exercise changes the shrimps' physiology: Muscles used for rapid tail flips use up oxygen, which needs to be replenished by blood flow. Therefore, increasing the volume of blood between muscle fibers causes more light to scatter and the shrimp to become opaque and visible.

"It's taken for granted that see-through animals are transparent all the time, but that's actually not the case. In these complex animals that are full of muscle, transparency can be disrupted and my study gets at one cause of that disruption," Bagge said in a statement.

To confirm her findings, Bagge conducted another experiment, in which she gave the shrimp small wounds. This caused blood to pool at the wound sites, which subsequently turned opaque, while the rest of the animal remained transparent.

The results of their study were recently presented at the 2016 annual conference of the Society of Integrative and Comparative Biology in Portland, Oregon.

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