When observing certain lizards, a brightly colored flap of skin often extends suddenly from the throat. This specialized structure is a visual communication tool, often exhibiting vivid reds, oranges, yellows, or blues. It plays a fundamental role in the social life of the reptile, signaling intent and status without physical confrontation.
The Anatomy of the Dewlap
The structure is scientifically known as a dewlap or a gular fan, an extendable fold of skin located beneath the lower jaw. This flap is inconspicuous when the animal is at rest, but snaps into a prominent display when activated. The vibrant coloration is derived from pigments like pterins and carotenoids, which help the display stand out against background foliage.
The mechanism for extending this flap is rooted in the lizard’s specialized hyoid apparatus, a complex of bone and cartilage found in the throat. This apparatus, which supports the tongue, is modified to act as a lever. Elongated skeletal elements, the second ceratobranchials, swing forward and down when muscles contract. This rotation unfurls the skin, transforming the relaxed throat into a broad, eye-catching signal.
Communication and Behavioral Function
The primary purpose of the dewlap is to facilitate visual communication over short to medium distances in environments where scent or sound signals are less effective. One of its most frequent uses is in the establishment and defense of territory. A male lizard will flash its dewlap at a rival male (a conspecific) to signal dominance and warn against intrusion, often making the animal appear larger and more formidable than it truly is.
Gular displays are coupled with rapid, rhythmic body movements, such as head-bobbing or “push-ups,” which increase the signal’s visibility. The combination of bright, moving color and body posture communicates a threat display, often allowing the dominant lizard to deter a rival without a physical fight. The bright color is important in dense, shaded habitats, as it stands out even in low-light conditions.
The dewlap is also instrumental in courtship and sexual selection, serving as a display to attract potential mates. Males use the extended fan to advertise their presence, fitness, and species identity to females. The size, color, and pattern of the dewlap, along with the specific cadence of the accompanying head-bobbing, are all factors that a female uses to assess the male’s quality and determine whether he is of the correct species.
Species Known for Gular Displays
The most prominent and well-studied examples of lizards using this gular display belong to the genus Anolis, commonly known as anoles. These small, arboreal lizards are found throughout the New World, with species like the Green Anole (Anolis carolinensis) and the Brown Anole (Anolis sagrei) being highly recognizable for their brightly colored throat fans. The dewlap in anoles is highly sexually dimorphic, meaning it is typically large and colorful in males, while often being absent or very small in females.
Within the Anolis genus, the color and pattern of the dewlap vary dramatically between species, ranging from solid pink, red, or yellow to intricate patterns. This species-specific variation is crucial for reproductive isolation, ensuring that a male’s signal is recognized only by females of his own species. Similar, though often less elaborate, gular displays are also seen in other groups of lizards, including some species of iguanas and agamas.