Glass squid’s ‘leaky’ light gives lesson in biology

Squids may have something to teach us about making the most of a messy situation.

The glass squid is a small deep-sea animal whose body is nearly completely translucent to help it avoid predators. The squid’s only readily apparent, opaque feature is its dark eye spots. Scientists had reasoned that an organ known as a photophore keeps the squid camouflaged through redirecting light around the eye to help it blend in with the natural light of its environment.

Alison Sweeney, an assistant professor in the Department of Physics & Astronomy in the School of Arts & Sciences, and postdoctoral student Amanda Holt, investigate how deep sea creatures interact with light. They wanted to know just how this photophore rearranges natural light to camouflage the squid.

They were surprised to find that that transmission of light through the photophore was a very “leaky” system.

“The photophores are meant to protect them from predators that are looking up and seeing shadows from the bright down-welling light,” Holt says, “but there’s also light coming [out] from the sides.” 

From an engineering standpoint, this light leaking out the sides of the squid before reaching the end of the system would be considered inefficient. But when Sweeney and Holt modeled how light travels in the squid’s natural environment, they found that the leaking is actually advantageous.

Because of leaks in the system, the squid is able to better blend into its environment from many angles. And because of differences among the different kinds of cells in the photophore, they can replicate this camouflage in different water qualities.

“In general, animals are a lot more sophisticated in the ways they use light than we give them credit for,” says Sweeney.  “You also have to have a fair bit of biological insight to know what might be going on and fully understand them.”

The messiness of biological systems like the photophore may help to shed light on a persistent problem in engineering: creating materials on the nano scale.

“In the nano field—where engineers are trying to get control of structures at single to tens of nanometer length scales—it’s hard to scale those processes,” Sweeney says. “You can make a very small batch of some really, really nice well-controlled ones, but then as soon as you try to make more you lose that small scale control.”

Sweeney says that biology is a source of solutions to this problem, since the effectiveness of systems like in the photophore has been proven by natural selection. The trick may be in allowing for a certain amount of messiness.

“If you can more or less make one thing and then a controlled number of variants of that thing, you can actually use that to your advantage to make something that has more functionality than the completely controlled version would have had,” Sweeney says. “I think looking to biology to leverage the mess in some sense can help us better understand how to better take advantage of, rather than completely get rid of, mess in nanofabrication techniques.”