Chromatophores are specialized pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and cephalopods. When rubbed or stimulated, chromatophores can rapidly change color, creating fascinating and visually striking effects on an organism’s appearance.
If you’re short on time, here’s a quick answer to what happens when you rub chromatophores: rubbing or stimulating chromatophores leads to rapid color changes in surface cells and tissues as the pigments within the chromatophores disperse or concentrate.
In this comprehensive article, we will explore the structure and function of chromatophores, the mechanisms behind their color-changing abilities, and specifically what occurs at the cellular level when these chromatophores are rubbed or stimulated.
Chromatophore Structure and Function
Chromatophore Types and Pigments
Chromatophores are specialized pigment-containing and light-reflecting cells found in many fish, amphibians, reptiles, crustaceans, and cephalopods like squid and octopuses. There are several different types of chromatophores, each containing their own unique pigments that allow the animal to change its color and pattern.
Here are some of the most common chromatophore types:
- Melanophores – Contain black or brown melanin pigments
- Xanthophores – Contain yellow xanthine pigments
- Erythrophores – Contain red erythrine pigments
- Cyanophores – Contain blue pigments
- Leucophores – Contain reflective purines that produce white colors
- Iridophores – Contain crystalline purines that produce iridescent colors
These pigments are contained within organelles called melanosomes. By aggregating or dispersing melanosomes using the cytoskeleton, the cell can change its color and reflectance. For example, aggregating melanin in a melanophore will make it appear darker, while dispersing the melanin makes it appear lighter.
The variety of chromatophore types and pigments allows animals to create complex color patterns for camouflage and communication.
The Cellular Mechanics Behind Chromatophore Color Changes
Chromatophores change color using a fascinating cellular process that allows pigments to be translocated within the cell on demand. This process relies on the cytoskeleton, motor proteins, and signaling from the nervous system.
Within each chromatophore are hundreds of sac-like melanosomes containing pigment. These melanosomes are linked to microtubule filaments that make up part of the cytoskeleton. When the cell receives a signal to change color, motor proteins called dyneins “walk” along the microtubules carrying melanosomes towards the center or periphery of the cell.
- Centering melanosomes makes the cell appear lighter or less colorful, since pigments amalgamate and reflect less light.
- Dispersing melanosomes towards the periphery makes the cell appear darker or more vibrant, since the pigments are spread through the cytoplasm.
These color shifts can happen quite quickly – some cephalopods like squid can completely change their appearance in just a few seconds! The speed and coordination of thousands of chromatophores allows for dynamic camouflage and intricate displays.
The chromatophore changes are controlled by the brain and nervous system via hormones and neurotransmitters. For example, in fish chromatophores may react to melatonin levels, while in cephalopods they respond to neural and endocrine signals. This allows animals to consciously control their colors.
The Effects of Rubbing Chromatophores
Mechanical Stimulation Triggers Hormonal Signals
Chromatophores are specialized pigment-containing and light-reflecting cells found in fish, amphibians, reptiles, crustaceans and cephalopods (1). They allow animals to change skin color for camouflage, communication, thermoregulation or ultraviolet protection.
Mechanical stimulation or rubbing of the skin triggers internal hormonal signals that cause pigment dispersion or concentration within the chromatophores (2).
For example, stress hormones like cortisol and adrenaline can initiate pigment dispersion as part of an animal’s fear response. By contrast, rubbing that mimics mating behavior may release reproductive hormones triggering aggregation of pigments within the chromatophores (3).
The effects are rapid and reversible.
Pigment Dispersion and Concentration
Chromatophores contain vesicles filled with differently colored pigments like melanins (black/brown), carotenoids (red/yellow), pteridines (red/white) or reflectins (iridophores causing iridescence) (4).
When stimulated, pigment sacs move towards the periphery dispersing color across a larger surface area. When relaxed, pigments contract towards the center concentrating color into a smaller space (5). These changes happen via microtubule reorganization within chromatophores.
Interestingly, some species can selectively disperse one type of pigment without affecting others allowing complex and dynamic color shifts. Dispersion state also interacts with ambient light properties, structural colors and anatomical features (e.g.
skin folds or iridophores) to generate further optical effects.
Differences Across Chromatophore Types
While all chromatophores demonstrate dispersion/concentration, exact mechanisms differ across cell types:
- Melanophores use actin filaments transporting melanin via motor proteins.
- Erythrophores and xanthophores rely on microtubules shuttling pigments in vesicles.
- Iridophores have protein platelets that reflect/scatter light. Platelet position affects iridescence.
Furthermore, non-pigment mechanisms like skin folding, erythrophore broadband reflectors and iridophore diffraction grating adjustments enable additional rapid color change abilities (6).
| Chromatophore Type | Key Pigments | Color Change Mechanism |
| Melanophores | Melanins (black, brown) | Actin filaments move melanosomes |
| Xanthophores | Carotenoids (red, yellow) | Microtubules shuttle pigment vesicles |
| Iridophores | Reflectins, purines (iridocytes) | Reflective platelet repositioning |
Evolutionary Advantages of Rapid Color Change
Camouflage and Mimicry
The ability to rapidly change color provides critical evolutionary advantages to organisms with chromatophores. A key benefit is camouflage, allowing an animal to blend into its surroundings to avoid predation.
For example, the octopus can seamlessly match the colors and patterns of rocks, sand, and coral to conceal itself from prey and predators (Reference). Chameleons also leverage quick color changes to camouflage themselves amid leaves and twigs.
Beyond camouflage, mimicking the colors of dangerous species via rapid chromatophore adjustments can ward off predators. Multiple harmless snake species closely copy the vibrant red, yellow, and black banding of deadly coral snakes to protect themselves.
Communication and Social Signaling
The chromatophore system further enables complex communication and social signaling essential for survival and reproduction. Squids utilize chromatic, postural, and locomotor signals during courtship and spawning, with males exhibiting dynamic color and texture patterns to attract females (Reference).
The Caribbean reef squid flashes red and white to signal aggression between competing males. Additionally, cephalopod hatchlings may leverage chromatophore fluctuations to facilitate schooling and coordinating movements with siblings.
Thermoregulation
Rapid color change also plays a thermoregulatory role for some species. For example, bearded dragons and chameleons darken their skin to absorb heat from sunlight, while becoming paler to reflect radiation and cool down.
According to a study, shifting skin darkness by just 10-20% enables effective temperature regulation to suit environments. This mechanism lets the Panther chameleon thrive across a range spanning over 60°F.
Some cephalopods like octopuses may also leverage chromatophore adjustments to support thermoregulation needs.
Conclusion
In summary, when chromatophores are rubbed or stimulated, complex hormonal signaling and cytoskeletal mechanics within the cells cause the pigments to quickly disperse or aggregate, leading to dramatic changes in an organism’s coloration and appearance.
The ability to rapidly transform color has evolved to serve essential functions related to predator avoidance, mating rituals, temperature regulation and more. Understanding the physicochemical basis behind chromatophore color shifts continues to be an active area of research with promising applications in bioinspired optics and adaptive materials.
