Everybody likes cuttlefish, it seems. They’re neat-looking, sociable, and display lots of entertaining behavior. I think it’s about time, then, to start talking about what cuttlefish do best: change color! I’ll start at what is, as far as I can tell, the beginning.
In 1988, Roger Hanlon and John Messenger published a paper called “Adaptive Coloration in Young Cuttlefish (Sepia Officinalis L.): The Morphology and Development of Body Patterns and Their Relation to Behaviour.” This paper lays out a description of the body-patterning behavior of young cuttlefish (S. officinalis), paving the way for many future studies on this behavior and the environmental features mediating it. The authors hatched and raised “more than 50″ cuttlefish, recording their behavior while they were in the laboratory, and then releasing them into the sea and videotaping them. From this (very large) set of data, they developed a systematic description of the various components of cuttlefish body patterns, as well as some ideas about what adaptive function they serve to the cuttlefish to use them. In addition, they did some microscopic analyses of the animal’s brains and skins, which I will spend less time on here.
The authors decided, based on precident as well as their own ingenuity, to describe the body patterns of cuttlefish (that is, the patterns of postures and colors that cuttlefish display) using a hierarchical scheme. In this scheme, each body pattern corresponds to one or a few behaviors, during which it is expressed. The body pattern is itself composed of multiple components – it has chromatic components (specific patterns of coloration,) textural components (specific patterns of skin texture,) postural components ( specific ways the cuttlefish holds its body,) and locomotor components (the ways the cuttlefish moves its body during the display.) Each of these components is made up of several units. The term “unit” as used here refers to a group of muscles that acts together to produce a local effect, many of which add up to become a body pattern component. For example, the group of muscles in each arm that hold that arm in a certain position make up a postural unit, and all of the postural units (that is, all of the arm and mantle muscle groups) together make up a postural body pattern component. Each unit is in turn made up of a number of elements, which are the smallest possible pieces that can display a particular tiny piece of a body pattern – for example, a single arm or skin muscle, or a single chromatophore. If that confused you, just take a look at their first figure, diagramming this concept:
Click through for a larger version.
The authors identify 54 components in all: 34 chromatic components, 6 textural components, 8 postural components, and 6 locomotor components. They also identify 13 distinct body patterns that are made out of these components: 6 chronic patterns (those expressed stably for a long time) and 7 acute patterns (those expressed transiently, usually in reaction to some significant or disturbing event.)
As an aside, I’d like take a moment to throw around a few counter-arguments to a common abuse of this line of research – namely, the claim that people like to throw around that cuttlefish and squid have a “language” that they express with their skin.
Firstly, cuttlefish displays are not symbolic – a cuttlefish who displays (for example) a pattern associated with mating is symoblizing sex, or the desire to have sex – the fact is that cuttlefish that want to have sex behave in a particular way. Calling this language is like saying that your dog is speaking to you when he humps your leg. He’s not telling you that he wants to have sex – he’s just doing what amorous dogs do.
Secondly, cuttlefish displays do not seem to have syntax. One of the things that makes language useful, and indeed defines language, is the ability to use various components of that language in novel ways, to communicate novel ideas. Related to this is the fact that the meanings of symbols are arbitrary – they can change, and do not neccessarily resemble or otherwise relate to whatever is being symbolized. There is simply no evidence that cuttlefish body patterns are this flexible, or ever mean anything besides making the behaviors they are part of more distinctive or effective. They may serve as an avenue of communication between conspecifics in some instances (in fact, they almost certainly do) but it is woefully inaccurate to describe them as language, especially without any further qualification.
Even if cuttlefish body patterning were a language, it would be a poor one. In most languages, a small number of symbols are used in various combinations to make a variety of units of meaning. For example, letters combine to form words, which combine to form short phrases. In english, there are 26 letters and many thousands of words and short phrases. Combining letters generates new information, not contained in the individual letters. The transition from components to body patterns in cuttlefish, on the other hand, causes information to be lost. Out of many components, cuttlefish put together only a few units of meaning.
So dear internet: I know how much you love cuttlefish, and I know that you want everybody else to love them, too. Exaggerating the evidence to make them seem more “intelligent” is not a valid way to do this, and makes you look unintelligent, dishonest, or both. Please, for your own good and the good of cephalopods everywhere, stop.
Anyways, back to the paper:
What do cuttlefish use these body patterns for? Most of the chronic body patterns are used for crypsis, or camoflage. A cuttlefish will use these patterns to blend into whatever is around them, so that they don’t get eaten. The plate below shows three cuttlefish in different developmental stages blending into the same substrate. The youngest one (towards the bottom of the photograph) is showing (as well as I can tell) a “strong disruptive” pattern, made up of highly contrasting dark and light components. The next oldest one (towards the top of the photograph) is showing a “weak disruptive” pattern, with the same basic scheme but with less contrast. The oldest one (right in the middle) is showing a “dark mottle” pattern, which is just what it sounds like:
When hiding fails, cuttlefish will show a variety of acute patterns in defense. Included among these are “uniform blanching” and “uniform darkening”, both of which are used to confuse would predators. A posture called “flamboyant”, where the cuttlefish waves its arms in the water, is used to startle predators. Adult cuttlefish use a pattern called the “deimatic” pattern, where the cuttlefish flattens and turns completely white except for a few dark markings on the mantle is theorized to be a sort of bluff: it makes the cuttlefish look bigger, and (hopefully) frightenes whatever predator is pursuing the cuttlefish enough to drive it off.
Patterns called “zebra” and “intense zebra” are used in social behavior, which primarily consists of sexual behavior and agonistic behavior (fighting or aggressive displays.) Variations on these patterns are used to distinguish between males and females. The picture below shows a male displaying the “intense zebra” pattern to a female. The authors note the critical inclusion of the extended and densely patterned fourth arm (the one most towards the bottom of the photograph,) the absence of which is one of the things that distinguishes the female “zebra” display from the male “zebra” display.
Click through for a larger version.
Finally, (and this is what I like best about this paper,) the authors close with a call for work “towards a comparative cephalopod ethology.” I can’t say it any better than they did:
It is clear from our work and [others] that cephalopod body patterns are inextricably linked with cephalopod behaviour so that study of body patterns becomes central to cephalopod ethology…
Recently there has been increased interest in ecological studies of cephalopods and we hope field researchers will begin to record systematically ethological data such as adaptive coloration, with the long-term goal of providing a more comprehensive view of their behaviour and life style.
Thanks for reading! I only covered this paper in the roughest way, so I urge those who want to know more to check it out – it’s available from Royal Society Publishing.
Hanlon, R., & Messenger, J. (1988). Adaptive Coloration in Young Cuttlefish (Sepia Officinalis L.): The Morphology and Development of Body Patterns and Their Relation to Behaviour Philosophical Transactions of the Royal Society B: Biological Sciences, 320 (1200), 437-487 DOI: 10.1098/rstb.1988.0087