When the words "chameleon" or "octopus" immediately arises an association with bright colors that change each other. Green foliage and grass, colorful flowers and fruits, a variety of colors for aquarium fish and amazing color animals. All this is the world that surrounds us. Living organisms owe this multicolor to special cellular structures - chromatophores. What are these strange entities, what is their function and how do they work - this article is about this.
Color bearing
This is how the word "chromatophores" is translated. What is this substance, it is worth explaining in accordance with various groups of living organisms. In crustaceans, mollusks, fish, amphibians, reptiles, these are reflective cells and cells containing pigment. They are responsible for the color of the eyes and skin and are formed only during embryogenesis in the neural crest. After a ripening period, they spread throughout the body. By tone in white, they are divided into cantophores (yellow), erythrophors (red), iridophores (radiant), leucophores (white), melanophores (black or brown). The structure of the chromatophore in different groups is different, and we will return to this question below.
Photosynthetic Plastids
What are algal chromatophores? These are single-membrane organelles of brown and green algae ribbon or star-shaped, containing colored granules (chlorophylls and carotenoids). In microorganisms and bacteria, these are membraneless organelles of very different shapes and for different purposes. For example, the chromatophore of chlamydomonas is represented by a chloroplast in the form of a bowl (starch is stored in it) with a red pigment body containing a hematochrome (red pigment). Thanks to him, this simplest one has the ability to sense light. In a unicellular alga chlorella, the chromatophore is represented by granules of chlorophyll-a and chlorophyll-b, floating in large numbers in the cytoplasm of the cell. With their help, this algae provides the most effective photosynthesis from a minimum of resources. Thus, it is characteristic of protozoa and unicellular algae that, in addition to the photosynthetic function of the chromatophore, it is storage and photosensitive. It is worth noting that algal chromatophores differ from higher plant chloroplasts in a simpler structure and other types of chlorophyll (green pigment with a magnesium complex).
Pigment cells of animals
In humans and many animals there are cells containing only one pigment - melatonin. These cells are found in the skin, hair, hair and feathers, in the iris and retina. The color saturation depends on the concentration. These cells are called chromatocytes, they are formed throughout the life of the body and can only be of one type - melanocytes.
Work specifics
What are chromatophores? The idea of their work, which is necessary for their classification, was formed in the 60s of the last century. Recent biochemistry data have not changed these provisions, but clarified the principles of their work. Two types are distinguished in chromatophores: biochromes and chemochromes. The first are true (real) pigments - carotenoids (various carotene derivatives) and pteridins. They absorb one part of the visible light and reflect the other. Structural colors (chemochromes) form color by interference or scattering (reflection of waves of one length and transmission of waves of another length).
Color classification
The division of the chromatophore by color is rather arbitrary. And that's why. Xanthophores and erythrophors can be contained in one cell, and then its color will depend on the amount of yellow and red pigments. Iridophores are chemochromes containing guanine crystals. It is crystals that reflect light and give an iridescent color. Zumellanin melanophore has a high light-absorbing ability and forms black and brown colors.
The biological role of pigments
Melanin, the most common pigment in living organisms, acts as a shield cell by absorbing light. It does not transmit ultraviolet rays into the deeper layers of the skin, protecting internal tissues from radiation damage. The role of pigment in the adaptive mechanisms of living organisms cannot be underestimated. What is a chromatophore in the life of pollinating insects and the plants pollinated by them is known to everyone. Body coloration plays an important role in protecting against enemies, tracking prey, warning of danger, and reproductive behavior. Chlorophyll, bacteriorhodopsin are photosynthetic pigments, and hemoglobin and hemocyanin are respiratory chromogens.
Property to change
The most interesting and mysterious phenomenon is the change in color of some animals. This phenomenon is called physiological color change. This mechanism is complex and continues to amaze scientists. Quite a lot of representatives of various phylogenetic branches in the process of evolution gained this ability. Chameleons and cephalopods (octopuses and cuttlefish) are quite distant organisms in the evolutionary ladder of life, but unconditional leaders in the ranking of the most "volatile". This is surprising, but the mechanisms of work of the chromatophores are the same.
How do they do it
Some representatives among cephalopods, arthropods, crustaceans, fish, amphibians and reptiles have elastic cells under the skin, such as rubber. Their chromatophores have a membrane and are filled with paint, like watercolor tubes. Each such cell at rest is a ball, and when excited, it is a disk stretched by many muscle expanders (dilators). They stretch the chromatophore, increasing its area many times, sometimes sixty. And they do it very quickly - in half a second. In chromatophores, pigment grains can be located in the center or be scattered throughout the cell, they can be many or few. Each dilator is connected by nerves to the command post - the brain of the animal. Color changes occur under the influence of two groups of factors: physiological (changes in environmental factors or pain) and emotional. Fright, aggression, sympathy for the opposite sex and intense attention - all these emotional experiences change the color of the animal.
Process cytology
When the animal is at rest, all pigment grains appear in the center and the skin becomes light (white or yellowish). It is such a frosted glass that cuttlefish with a black spot of an ink bag looks like. When the dark pigment appears in the branches of the chromatophore, the skin becomes dark. The combination of pigments of various layers and gives the whole gamut of shades. Green and blue colors result from the refraction of light in guanidine crystals in the upper layers of the skin. Skin color can quickly change and capture the entire body or its parts, sometimes creating a very bizarre pattern. In addition, the chromatophores themselves can sink into the deeper layers of the skin or rise to the surface.
Chief Commander - Eyes
Scientists have established a close relationship between vision and color change. Light through the organ of vision acts on the nervous system, and it gives signals to chromatophores. Some are stretched, others are reduced, and at the same time, the maximum correspondence of paints for masking is achieved. It is interesting that even a blinded octopus can change color - it perceives color also with suction cups, and if at least one remains, the octopus will change color. It's amazing what bizarre patterns he can repeat on his body. There is evidence that the octopus was able to reproduce in a second the text of the newspaper, which was next to the aquarium. And it looks like mysticism.
Some interesting facts
In addition to the amazing ability of octopuses and chameleons to change color, they also have some more amazing features that you did not know about.
The octopus brain is the most developed among invertebrates. The largest octopus weighed 180 kilograms. It was 8 meters long (caught in 1945). Some octopuses can walk on land, resting on tentacles.
One of the most poisonous animals on the planet is the deep-ringed inhabitant of the Indian Ocean. After his bite, a person dies within 1.5 hours. But there is no antidote.
The smallest chameleon is Madagascar brukesia with a size of less than 3 centimeters, and the largest is Malagasy, grows up to 70 centimeters in length. They are practically deaf, but they will see the smallest insect at a distance of 10 meters. The angle of their vision is 360 degrees, and each eye sees its own picture of the world.