Speaking Squid: How Squid Glow to Communicate in Dark Oceans
The deep, open ocean may seem like an inhospitable environment, but many species like human-sized Humboldt squids are well-adapted to the harsh conditions. 1,500 feet below the ocean's surface, these voracious predators could be having complex conversations by glowing and changing patterns on their skin that researchers are just beginning to decipher.
In a study published Monday in the Proceedings of the National Academy of Sciences of United States of America, scientists from Stanford University and the Monterey Bay Aquarium Research Institute (MBARI) captured and analyzed footage of Humboldt squids off the Northern California coast using unmanned, robotic submarines called remotely operated vehicles (ROVs) to better understand this squid's visual communication.
Humboldt squids hunt in groups, and their collective foraging has been described as a "feeding frenzy." The ROV footage and new research, however, suggest that the squids actually communicate with each other as they hunt and socialize. They do so by changing patterns of light and dark pigmentation on their skin, the study shows. The changes can be seen even in pitch-black deep ocean because the squids make their entire bodies glow in the dark, reports MBARI.
Humboldt squids have numerous, small bioluminescent organs called photophores embedded subcutaneously throughout their muscle tissue that make them glow, the study's abstract explains. They use this "backlighting" to "boost the contrast" for skin patterning changes, says a Stanford University news report.
Chromatophores, or pigment cells embedded in the skin, create those pattern changes, reports Scimex. MBARI reports how those are then "backlit like words on an e-reader screen."
"Maybe they need this ability to glow and display these pigmentation patterns to facilitate group behaviors in order to survive out there," suggests study collaborator Ben Burford in the Stanford report. "Many squid live in fairly shallow water and don't have these light-producing organs, so it's possible this is a key evolutionary innovation for being able to inhabit the open ocean."
Burford and senior author Bruce Robison compared where the light organs are in Humboldt squid to where the most detailed skin patterns appear. They found an overlap of where the most densely-packed photophores were and where the most intricate patterns occur, the Stanford report explains. The finding lends weight to their hypothesis about the squids' evolution and use of background glow and changing skin patterns to communicate, the study postures.
Burford analyzed ROV video of 30 Humboldt squids, identifying individuals and observing their interactions. Keeping track of behaviors and skin patterns while squids were swimming alone, in small and large groups and while feeding, Burford realized that Humboldt squids exhibit specific color patterns when interacting with one another in groups, reports MBARI.
The scientists suggest these color changes are a way for the squids to communicate with one another. MBARI explains that a half-light/half-dark pattern that Humboldt squid often display while feeding could be a warning: "Look out — I'm going to grab that lanternfish!"
The squids are able to move through the darkness with exceptional precision, never colliding or competing for prey, the Stanford report notes. "This suggests that their pigmentation changes may be an effective means of communication, analogous to humans using turn signals in traffic," explains MBARI. Scimex reports that the changes could be a "signaling of intent during competitive foraging."
The scientists also found that the squids used patterns in specific sequences, "similar to how humans arrange words in a sentence," describes MBARI. A small sample size prohibited the researchers from understanding the meaning of these sequences, but they believe that certain patterns modify the meaning of other patterns, creating a form of "syntax" or something akin to an alphabet, MBARI continues.
In squid talk, "One sequence of patterns might mean 'Look out! — I'm going to grab that lanternfish,' but a different sequence might mean 'Look out! — If you don't get out of my way, I'm going to eat you!'" reports MBARI.
Though the exact meaning of the signals remains unknown and though it is too early to conclude whether the pattern changes constitute a "human-like" language, the findings suggest that the squid communications could be a complex form of animal communication never-before described in deep-sea animals.
Burford concludes, telling MBARI, "What I like about this paper is that we're investigating really basic questions about life in the deep sea. Even though the deep sea is the Earth's largest habitat, it's also the least known. So we're still making a lot of exciting discoveries in natural history and animal behavior."
The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.
"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."
The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.
They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.
They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.
But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.
"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.
What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.
It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.
To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.
First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.
Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.
University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.
"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."
Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.
"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.
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