Lizards do change colors, but this ability is not shared by every species within the vast lizard family. This physiological phenomenon, where a lizard can alter its skin hue, is a specialized survival trait found predominantly in specific groups like chameleons and anoles. The change is a dynamic process, driven by internal physiological signals rather than a conscious effort to perfectly match every background.
The Biological Machinery Behind Color Change
The ability to shift skin tone begins at the cellular level within specialized pigment cells called chromatophores, which are located in the lizard’s dermis. These cells are organized into layers, forming a functional arrangement known as the dermal chromatophore unit. This unit typically consists of three main cell types stacked one upon the other.
The deepest layer contains melanophores, which hold the dark pigment melanin in small packets called melanosomes. Overlying the melanophores are iridophores, structural cells that contain light-reflecting crystal platelets, often made of guanine. These platelets scatter light to create bright, iridescent, or blue colors. The topmost layer features xanthophores, which contain yellow and red pigments.
Color change is achieved by the rapid movement of pigment granules within these cells, a process called physiological color change. When a lizard needs to darken, hormonal or nervous signals cause the melanosomes in the melanophores to disperse outward, covering the overlying iridophores and xanthophores. This dark screen absorbs light, resulting in a darker appearance. Conversely, when the lizard lightens, the melanosomes aggregate back into the center of the cell, uncovering the reflective iridophores. The spacing of the crystal platelets within the iridophores can also be adjusted, changing the way light is scattered and resulting in shifts in structural colors.
Functional Roles of Shifting Hues
The primary function of color change is not always camouflage, though blending into the background is a benefit for many species. Color shifts are most frequently triggered by the need for thermoregulation, which is how these cold-blooded animals manage their body temperature. Lizards will often darken their skin when they are cold to increase the absorption of solar radiation, helping them warm up faster. Once a lizard reaches its optimal internal temperature, it will lighten its skin to reflect more sunlight and prevent overheating. Studies show this ability to change color for thermal regulation can significantly reduce the amount of time a lizard must spend basking.
The second major role is social signaling, where color change acts as a form of nonverbal communication among individuals. Lizards use rapid shifts in hue to convey messages about their emotional state, dominance, or reproductive readiness. During mating season, male lizards often display bright, high-contrast colors to attract females or to intimidate rivals. Aggressive encounters between males frequently involve a display of the darkest coloration to establish a clear dominance hierarchy. Color changes can also be partitioned to different body regions, such as the throat or beard, allowing the lizard to simultaneously regulate temperature with its back while using its neck for social communication.
Species That Utilize Rapid Color Shifts
The most famous examples of this phenomenon are chameleons, which possess an advanced ability to quickly manipulate the spacing of crystals within their iridophore cells to produce vibrant, iridescent colors. They use these shifts primarily for social signaling and regulating their body temperature, with camouflage often a secondary effect. Their color changes are complex, communicating information about their mood, such as fear, excitement, or a willingness to mate.
The Carolina anole, sometimes mistakenly called the American chameleon, also demonstrates a notable color-changing capacity, shifting between a bright green and a deep brown. This shift is slower than a chameleon’s, often taking several minutes, and is triggered by temperature fluctuations, stress, or social interaction, such as displaying their prominent dewlap.
The bearded dragon (Pogona vitticeps) exhibits a more localized form of color change. They can darken their dorsal surface for faster warming, while their throat and “beard” area can change dramatically from a pale color to jet black during social displays of aggression or territorial defense.