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Red Devil's Tongue: Chromatic Communication in the Dark



The transmission of information to humans has always been one of the main social aspects of existence. With the evolution and development of technology, information transfer methods became more and more. Once they were rock paintings, now just click a couple of buttons on your smartphone and the person on the other side of the planet will receive news from you. But communication between individuals is not the only method of transmitting information: paintings, symphonies, sculptures, etc. All this is also a form of transmission of certain information, an idea, laid down by the creator in his creation.

In the wildlife world, different species also transmit information to each other in a variety of ways: from verbal to tactile. However, many of these information signals are directly dependent on the habitat of the animal. Given this, the question arises - how do the Humboldt squids manage to communicate with each other at a depth of 700 m in the twilight zone, where total darkness prevails? A group of scientists from Stanford University found the answer to this question by observing the collective hunting of these amazing deep-sea predators. What are the features of squid communication and how complex is their information network? We learn about this from the report of the research group. Go.

Study basis


Before you begin to consider the study itself, it is worth getting a little acquainted with its main character.

Dosidicus gigas or Humboldt squid - a species of squid that lives in the waters of the Humboldt Current in the Pacific Ocean. He is a lonely representative of the genus Dosidicus from the subfamily Ommastrephinae (family Ommastrephidae ).


Dosidicus gigas

Squid Humboldt is considered one of the largest species of squid. He, of course, is far from the dimensions of his colossal relative, but Dosidicus gigas can grow up to about 2.5 m and weigh up to 50 kg.

In relation to humans, these creatures are not particularly aggressive, but for small fish, the Humboldt squid is a real disaster. Firstly, they are predators. Secondly, they travel through the ocean depths not alone, but with schools of up to 1200 individuals. The speed of the squid can reach up to 24 km / h.

The squid moves through a siphon through which they push the stream of water, as well as through the two fins on the top of the head (if I may say so about squids).

You can not talk about squids and not to mention their famous tentacles, or rather hands. In Dosidicus gigasthere are ten of them: eight for swimming and grabbing something, are covered with suction cups (about 200 each) and two, covered with cloves, to tighten the prey closer to its beak. The speed of the ejection of these two tentacles and the tightening of the victim is so fast that sometimes a person can successfully miss the whole process. If the prey is too big or excessively resists the inevitable death, the Humboldt squid can go down to great depths with it, where the pressure of the water column will do all the “dirty work”.


Dosidicus gigas during the hunt.

The large size and the presence of the awesome "toothed" tentacles already play against the reputation of Humboldt squids. In addition, many researchers call this species extremely aggressive in relation to everything that moves. Such characteristics in the summary served as the appearance of the corresponding nickname - “ diablos rojos ” (red devils). However, there is evidence that such behavior is inherent in this species exclusively during feeding. In other circumstances, the Humboldt squids are more curious than aggressive.


Another unique (and very frightening, especially thanks to this video) deep-sea squid is Magnapinna, which lives at a depth of about 2000 m.

Predatory nature, suckers, tentacles and beak are not all the features of Humboldt squid. They have one of the most unique ability in the animal world - to change color due to the special organ of photophores and chromatophore cells.

Changing your appearance can be useful both for hunting and for protection from predators. In the case of the Humboldt squid, it is also an excellent method of communication. True, before, no one could really explain exactly how and what they were talking about.

In order to examine in detail the color-light communication of squids, scientists conducted observations of their behavior in their natural habitat (California Current) at depths from 266 to 848 m using HD cameras attached to the ROV (remote-controlled uninhabited underwater vehicle).

Researchers note that Dosidicus gigas are not the only ones who can communicate collectively in the deep ocean. However, it was this species that was chosen for research, not only for their “unusualness”, but also for their cool attitude to ROV, in the presence of which they calmly continue to hunt, swim and communicate with each other. Consequently, the observation process itself will have a minimal effect on its results.

Scientists also note that Dosidicus gigasconstantly migrate vertically, spending most of the time in areas of the water column, where there is less light than on a moonless night on the surface of the ocean. Despite the virtually complete lack of lighting, all individuals in the squid flock communicate well, probably “discussing” various aspects of their behavior: where to look for food, when to start feeding, and how not to interfere with each other in the process.



A variety of chromatic (color) variations of the appearance of the squid Dosidicus gigas was also established , each of which can be regarded as a separate signal (image above).

In the process of observation, it was possible to photograph a group of 30 individuals that showed various nonrandom color options. An important word here is “nonrandom,” since this suggests that such permanent changes in color are not defects in shooting or thoughtlessly changing an individual's appearance for the sake of beauty, so to speak.

Research results


The first thing that was discovered after analyzing the observational data was the fact that D. gigas significantly more often use the chromatic signals “blink” (abrupt change from pale to dark color) and “flicker” (dynamic mosaic of diffuse pigmentation) in the presence of a large number of individuals its kind.


Image No. 1

Using the principal components method, scientists found that the dispersion of chromatic behavioral components in D. gigas at depth was related to the state of feeding (18.3%; 1A ) and the number of individuals (12.4%; 1B ). It follows from this that chromatic changes are signals during group activities.

Since Humboldt squids rely on color far more than on locomotion, scientists were able to isolate much more chromatic behavioral components than locomotor ones. Of the 18 chromatic components, thirteen appeared exclusively in the presence of a large number of relatives ( 1C ).

It is also curious that some of the color signals found in the Humboldt squid are also used by other species. For example, pale and dark areas along the longitudinal axis ( 1C and 1D ) are used during the breeding season by competing males of the Caribbean reef squid ( Sepioteuthis sepioidea ) and mourning cuttlefish ( Sepia plangon ).

Humboldt squids, who could become the best students of Hannibal Lecter, demonstrate this color during feeding (especially with insufficient food), when there are a lot of relatives around. It is likely that this is a kind of warning "do not bother me to hunt, dear relative, otherwise you will become prey."

It has already been suggested that some species of predators, hunting in groups, use certain types of signals to organize hunting in such a way as not to interfere with each other. This theory received its practical confirmation, since during the observation of squid it was clear that no matter how fast and randomly (at first glance) the group of individuals moved, they never came into contact with each other and never competed for prey. This behavior really makes sense, because there is no need to compete for food if there is a lot of it, putting yourself at risk of injury and giving this prey a chance to slip away. Each squid visually notifies its relatives that it attacks the prey, and this makes them understand that this particular prey is already taken and it is worth looking for another.

In addition to individual signals, which themselves can carry certain information, there is a syntax of signals, that is, different combinations of different signals that can also carry a certain meaning.

Of course, to say that cephalopods have their own language, similar to ours, would be an exaggeration. However, for example, two shallow-water squid species S. sepioidea and Sepioteuthis lessoniana demonstrate the use of syntax in the chromatic components of communication. As for D. gigas and other deep-sea species, their syntactic abilities have hardly been studied.


Image No. 2

During the observations, it was possible to fix the typical behavior of squids before capturing prey ( 2A and2B ). At the time of capture, D. gigas showed the typical squid locomotion ( 2D ) and body position ( 2C ), preceding and following impacts on prey ( 2E , 2G, and 2H ).

The ability to accurately capture the moment of an attack on a mining allows a better look at the chromatic signal components of this process.

Despite a small sample of observations (30 individuals), it was still possible to successfully analyze the obtained data and establish that D. gigas during hunting can consistently display chromatic components in a hierarchical manner, i.e. their varied color patterns have their own syntax.

The color of the squid that pursued the prey was predominantly dark (D), sandy (S) or painted according to the principle of “ anti-shadow ” * (CS).
“Shade” * (Thayer's law) - a variant of the masking color in animals when the upper body is darker than the lower.


One of Thayer's works entitled The Favorite Kitten.

Named after American artist and naturalist Abbot Henderson Thayer. He noticed that the parts of the body of animals that are more often turned to the light have a darker color than those that most of the time are in the shade.
However, right before the attack on the prey, the squid color changed to “attacking” pigmentation (BPD), when dark and pale areas alternate along the longitudinal axis ( 1C ). During the attack, the tentacles for prey changed color to dark (D), and then to pale (P) ( 2E and 2F ).

The above chromatic components were bright and noticeable, they are comparable with the words in the sentence. In addition to them, there were less noticeable color signals, such as punctuation marks: pale stripes along the lateral mantle (PLS) preceded CS; dark stripes on the tentacles (DAS) occurred before and after S; a dark spot on the head (SE) preceded BPD and followed CS; the darkened leading edge of the mantle (DMB) followed S, CS, and BPD ( 2F ).

If large and noticeable color signals can indicate the hunting process itself (finding prey, the moment before the attack and the attack itself), then the above mini-signals can indicate additional information (prey position and its type).

Together, all of these signals can form the basis of a squid flock hunting strategy.

During feeding (searching for prey and hunting for it), squids constantly showed a transition between the pale edges of the fin (PFE) and the dark edges of the fin (DFE), then between DFE and completely dark fins (DF) and, finally, back from DFE to PFE ( 2F ).

SE, DMB, the chromatic components of the fins, and the pale tip of the mantle (PVS) were displayed for a rather long time, comparable to the duration of signals of the S, CS, and BPD types.

These mini-signals may be related to the social aspect, and not to hunting, i.e. squids can use them to demonstrate dominance over other relatives. For example, the combination of DFE and SE signals in S. lessoniana (a type of reef squid) is a demonstration of the winner in fights between males.


Table of all detected chromatic signal variants.

Another theory of additional chromatic signals suggests that they are needed for self-defense. The observations were carried out using the ROV apparatus, which could be regarded by squids as a likely threat. And rapid changes in color and color patterns could serve as a distraction. Also, do not forget that this type of squid is famous for cannibalism.

The beauty and variety of color patterns on the body of the squid should go unnoticed by anyone, since their environment is devoid of light sources. However, for Humboldt squids this is not a problem, given the presence of bioluminescent backlight.

Typically, bioluminescent signals include changes in light intensity, they can be generated by changing conditions inside the photophores or by manipulating the emitted light through other anatomical features of the body.

Squids D. gigas would not be so curious creatures if they followed the classical tactics of bioluminescent deep-sea creatures. Instead of adjusting the light intensity, they use pigment patterns to selectively show and hide various areas of the fully luminescent body.


Image No. 3

While in most cases photophores are external and designed to project light outward, D. gigas photophores are instead internal and emit light in the muscle tissue of the fins, mantle, head and arms. Numerous (one D. gigas specimen may have hundreds) small subcutaneous photophores, which consist of relatively elementary clusters of photogenic tissue, penetrate into muscle tissue ( 3A - 3C ) and cause luminescence of the entire specimen.

Pigment patterns are formed due to these subcutaneous chromatophores. Thus, the squid can illuminate from the inside that color pattern that it demonstrates in order to more effectively transmit information to its relatives.

The anatomical study of several individuals showed that although photophores are distributed throughout the body, large clusters are located precisely in those parts of the body where the brightest and most important chromatic signals are shown (during capture of prey and during the presence of a large number of relatives).

It is worth noting that the ROV underwater spy camera and the human eye do not see like the eyes of the squid D. gigas . As their eyes see, it is still unknown exactly, although according to some reports it is believed that they can perfectly see in the dark at a distance of up to 1 meter. Scientists themselves intend to conduct a few more observations in the future with the use of more advanced cameras, which will allow us to see the change in pigmentation and bioluminescent behavior of squids as they themselves see it.

For a more detailed acquaintance with the nuances of the study, I recommend that you look into the report of scientists and additional materials to it.

Epilogue


One of the problems of studying the chromatic features of squid species D. gigas is their habitat. The bottom line is that observing squids in the wild does not always work out as scientists want: either squids are not enough to fully quantify the characteristics, then squid behavior does not correspond to their normal behavior due to the presence of ROV, etc. Observing squids in laboratory conditions also does not have any significant advantages, since the deep-sea species of the family Ommastrephidae , to which D. gigas belongs , are very difficult to carry up to the surface and live in captivity for very short periods. As a result, the poor animal dies, and scientists never get the data they need.

Nevertheless, in the study we examined today, scientists still managed to get some information regarding the communication of squids in extreme darkness. The first thing that catches your eye is the non-standard use of light. Most bioluminescent deep-sea creatures use precisely light to transmit information, regulating its intensity. Humboldt squids use light to illuminate their colored patterns on the body.

There are many variants of these patterns, combinations are even greater. Each pattern and combination of patterns carry a specific signal, information for relatives.

It is obvious that social beings in one way or another form a form of communication in order to transmit important information to each other. But communication methods are different not only in form and type, but also in complexity. Scientists boldly declare that the Humboldt squid communication network is quite complex and consists of many signals that they can build into whole sentences, that is, use syntax. Yes, the barefoots were always distinguished by their intelligence and quick wits, but scientists did not expect this.

The depths of the oceans have always been associated with mystery and unexplored. The creatures that live there also remain largely a mystery to us, however, the constant improvement of technology allows us to open the curtain of mystery.

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Thank you for your attention, stay curious and have a great weekend everyone, guys! :)

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