2023-06-29 02:15:31
many species of cephalopods they are able to camouflage themselves by adapting their appearance to the environment. For this they use a motor system that controls the expansion of several million cpigment cells of the skin, called chromatophores. The generation of skin patterns depends on the instinctive coordination of thousands of motoneurons that interpret complex visual scenes, a mechanism of which there are hardly any studies.
“This ability is possessed by some coleoid cephalopods, including cuttlefish, octopus and, to a lesser extent, squid,” he told SINC Guilles Laurent, scientist at the Max Planck Institute for Brain Research (Germany). The expert leads an observation work that suggests that, in the case of the common sepia (Sepia officinalis), this system is very flexible and adaptable, which provides new insights into this complex physiological process. The results of the study are published today in Nature.
“We studied how animals establish camouflage by observing and quantifying the change in the skin pattern, at chromatophore resolution, in hundreds of thousands of them, and over time,” adds Laurent.
Pigments are contained in these individual cells, or chromatophores, of the skin. Each of them is a cell whose diameter can be modified by a set of about 20 small muscles per cell. When the muscles contract, the diameter of the chromatophore increases. If they relax, it decreases. Thus, each chromatophore can vary between about 10 and 300 microns.
The muscles of each chromatophore are under the control of a motor neuron located in the brain. An adult cuttlefish has about a million chromatophoresTherefore, his skin is a visualization system, “a bit like a high-definition television screen, where the pixels are the chromatophores, and their control is by size rather than by intensity,” the scientist exemplifies. In cuttlefish, the pigments are of three colors: yellow, red, and dark brown.
“When an animal wants to hide from a prey or a predator, it first observes with its eyes the substrate it wants to match and controls the state of all its chromatophores with its brain. The ultimate goal is to match the texture or pattern of that substrate,” explains Laurent.
A very detailed copy
To learn about the camouflage behavior of these animals, they used natural and artificial backgrounds, gathering more than 200,000 images that were used to map the color change process at single-cell resolution. The data from these maps indicated that each pattern was highly detailed and that the same background could produce many different results.
“What we show is that animals generate a given camouflage differently each time (even for the same target substrate), and build it up progressively over many seconds, using a progressive approximation and improvement processinterrupted by stops, during which the animals seem to compare the state of their pattern with the one they are trying to match”, says the expert.
This assumes that they have a form of continuous feedback and the final camouflage is the product of successive bug fixing steps, indicating that the process is highly adaptive and does not follow a fixed path.
In the face of a threat they are quick and direct
The exception to this rule occurred during ‘scalding’, a defense mechanism in which cephalopods blanch in response to threatening stimuli. “They turn white and once the threat has disappeared, they return to their initial camouflage pattern,” says the researcher. It was observed that this process was quick and direct, and that the retained memory of the initial camouflage returned to expression once the threat was removed.
“The chromatophore system is used in many ways. When blanching, it serves to scare potential predators. We also studied bleaching using the same approach and found that it differs fundamentally from camouflage in that it is targeted, reliable, and superimposes a co-existing, attenuated pattern,” says Laurent.
These results provide valuable insights into how these coping mechanisms interact with each other and how the complex process of color matching is accomplished on a cellular scale.
References Gilles Laurent et al. The dynamics of pattern matching in camouflaging cuttlefish. Nature (June, 2023).
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