Biologists discover the secrets of “invisible” animals

This story at the origin Appeared on Dark Atlas and is part of Climate Office collaboration.

While hiking in the Peruvian rainforest, an eight-hour boat ride from the nearest jungle colony, biologist Aaron Pomerantz saw what appeared to be tiny invisible jets crossing the trail. “I was there with a net trying to catch things,” he said, “and these just changed direction and disappeared.”

It was his first close encounter with butterflies with pale wings, insects which inhabit the forests of Central and South America and which possess a remarkable means of camouflage: transparent or “glass” wings which make them particularly difficult to see. spot in the dense understory.

“It’s like the power of invisibility,” says Pomerantz, lead author of a recent study in the Journal of Experimental Biology which examines how clear wings develop. “If you can put on an invisibility cloak, it’s much harder for predators to find you.” In oceanic environments there are many transparent species, but on land it is much less common. And that really begs the question of “what does it take to be transparent on earth?” “”

By studying the wings of the species Greta oto, also known as the glass-winged butterfly, in various stages of pupa development, Pomerantz and his colleagues at the University of California at Berkeley, the Marine Biological Laboratory at Woods Hole, and Caltech found a few factors. There are changes in the shape and density of the microscopic scales that typically create the colorful patterns of a butterfly. A layer of tiny waxy pillars also acts as an additional anti-reflective coating.

If this sounds like a one-time adaptation, it isn’t. “It has evolved several times,” explains Pomerantz. There are several hundred species of butterflies and glass-winged moths, he notes. Although they represent only a small part of the order Lepidoptera, they constitute most of the rare cases of such transparency on land. Another example is glass frogs, which exhibit varying degrees of skin translucency.

The ocean, on the other hand, is teeming with transparent species, from jellyfish and sponges to crustaceans, cephalopods and even fish. Earlier in the summer of 2021, two rare sightings of a glass octopus were made during an expedition, aboard the Schmidt Ocean Institute research vessel Falkor, in the aquatic depths off the remote islands of Phoenix in the Pacific Ocean. It turns out that being invisible is much easier to achieve in the ocean than on land, in part because of the visual and physical properties of water.

“You can think of it like having a piece of glass in water,” says marine biologist Laura Bagge. “This environment is much less characteristic than it is on earth, and you don’t have to face gravity. So most of these animals are some sort of aquatic, floating thing with no backbones or dense structures needed to survive on land. “

Imagine this classic Jaws scene – that from the point of view of the shark – where the silhouette of a swimmer stands against the light which descends from above. Where the sun is shining, it’s easy for underwater predators to see opaque shapes, so being transparent helps you pass. Deeper in the ocean, it remains useful because even in the aphotic zone – depths where little or no sunlight penetrates – many bioluminescent animals emit their own light, Bagge says.

Now a senior biologist at Torch Technologies in Florida, Bagge became fascinated by animal transparency during a research cruise for her thesis at Duke University. She had dipped her hand into a bucket of sea creatures and extracted a mysterious specimen. “It was tough, like a lobster, but it was quite a clear animal,” she says. It was a crustacean resembling a shrimp, Cystisoma, which can reach the size of a human hand. “They are so cool because they have a tough outer shell and are full of muscle. How do you clarify this? “

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