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Speaking in colors

A look at the prismatic body language of squid

By Evan Lubofsky | September 23, 2021

A mating pair of squid swim through a spawning area in northeastern Taiwan. The larger animal, a male, displays a lined pattern across its body to communicate “let’s swim together” while the smaller, female squid uses spots. (Photo by Dr. Chun-Yen Lin, National Tsing Hua University)

The surprising social lives of squids

By Evan Lubofsky | September 22, 2021

A mating pair of squid swim through a spawning area in northeastern Taiwan. The larger animal, a male, displays a lined pattern across its body to communicate “let’s swim together” while the smaller, female squid uses spots. (Photo by Dr. Chun-Yen Lin, National Tsing Hua University)

When it comes to communicating our emotions, we humans have a lot of options. Particularly nonverbal ones. The moment we feel scared, territorial, excited, or yes, even smitten, we can say so with a limitless number of facial expressions, body language gestures, and eye gazes. Even emojis can do the trick. :\

Squid, it turns out, have a lot of options, too.

“Squid are very sophisticated, and have a wealth of color-patterning capabilities that they use for communicating and social interactions,” says WHOI associate scientist Aran Mooney, who has been studying squid and other cephalopods for nearly fifteen years.

Impressively, squid can draw from a collection of more than a dozen different body patterns. Whether lighting up for love or turning pale from fear, these enigmatic creatures apparently know when—and when not—to stand out from the crowd. They can spice up their fins with polka dots, send stripes down their bodies, or turn their tentacles black to blend in with the ocean's sunless depths.

Mooney has witnessed this body patterning phenomenon while investigating how squid respond to sounds in the ocean. Mainly human-made sounds like shipping noise, seismic surveys, and marine construction activity.

“With squid, there are a whole suite of color patterns and gradations we can see and evaluate to help determine how abrasive they find particular sounds,” Mooney says. “Impulsive sounds like pile-driving and other sources of construction noise tend to be the most abrasive to them. If they’re not too startled by it, they may turn a pale color. But when these sounds really startle them, they’ll often respond by showing rapid color changes and darker patterning.”

WHOI associate scientist Aran Mooney holds a year-old squid during experiments he conducted to measure the impact of sound on squid behavior. (Photo by Daniel Hentz, © Woods Hole Oceanographic Institution)

WHOI associate scientist Aran Mooney holds a year-old squid during experiments he conducted to measure the impact of sound on squid behavior. (Photo by Daniel Hentz, © Woods Hole Oceanographic Institution)

Surprisingly, squid can also display multiple colors and patterns to convey different emotions at the same time—a potential boon for their social lives. A male squid, for example, can use certain patterns to woo a female on its left while signaling “Keep your distance, pal!” to a male on its right.

WHOI fish ecologist Joel Llopiz recently put one of these social multitaskers under the microscope and recorded a video of the body patterning bonanza. Like the camouflage rock star that it is, the animal put on a dazzling light show, using its muscles to activate a series of pigment-containing cells, known as chromatophores. In the video, you can see tiny red, yellow, and black-hued sacs expanding and contracting across the squid’s see-through skin. The effect is dramatic.

But the mechanics behind these intricate body patterns are mysterious. Squid nervous systems are incredibly complex and researchers are only beginning to gain insights into the link between their neurons and the motor functions responsible for squid sign language.

In laboratory experiments, Dr. Chuan-Chin Chiao, a neuroscientist at National Tsing Hua University in Taiwan, used electrodes to stimulate the optic lobe of a species of squid known as the oval squid (S. lessoniana). Then he observed the resulting body pattern changes. To Dr. Chiao's surprise, he discovered a major difference between the way human brains and squid nervous systems are organized: in our brains, a single point controls the motor function of a specific body part, whereas with squid, there is no such one-to-one correspondence.

A squid uses its muscles to activate a series of pigment-containing cells, known as chromatophores. (Photo by Paul Caiger, © Woods Hole Oceanographic Institution)

A squid uses its muscles to activate a series of pigment-contained cells, known as chromatophores. (Photo by Paul Caiger, © Woods Hole Oceanographic Institution)

“We found no direct relationship between the optic lobe and the muscles responsible for changing color patterns,” says Chiao. “The optic lobe is the upper motor command center of the squid, but there are several lower motor centers in the brain to further control these patterns.”

Squid body patterning, it seems, is a bit more complex than Chiao and other researchers had previously thought. “We do not find any other animal group who has such a unique system,” he adds.

Mooney says Dr. Chiao’s work helps bridge critical gaps in our understanding of squid behavior, and reinforces the need to figure out how these sophisticated neurons work.

“These guys are set up differently from us in that they don’t have a centralized brain that is processing information cognitively,” says Mooney. “They’re more reactive and responsive to the environment.”

Given all the social interactions squid have on a day-to-day basis below the surface, that’s probably not such a bad thing.