Lizards often expand their throat, inflating a section of skin beneath the lower jaw. This distinctive behavior, while seemingly simple, serves various purposes. Understanding why lizards engage in this display reveals insights into their communication strategies and physiological adaptations.
Communication Through Display
Lizards expand their throats as a visual signal in social interactions. This behavior plays a role in territorial defense, where males use the display to warn off rivals and assert dominance. By puffing out their throat, often with head bobs and push-ups, they appear larger and more intimidating, deterring competitors without physical conflict. Anole lizards, for example, extend their brightly colored throat flaps, called dewlaps, when another male intrudes upon their territory.
Throat expansion also attracts mates, especially among males. They display their enlarged, often vibrantly colored, dewlaps to signal fitness and genetic quality to potential female partners. The dewlap’s size, color, and patterns convey information about a male’s health and desirability. Some species, like the red-headed agama, bob their inflated throats to captivate females.
Beyond intraspecies communication, throat expansion can warn predators. When threatened, a lizard might inflate its throat to appear larger and more formidable. This defensive display deters predators by suggesting the lizard is too big to swallow or too challenging to pursue. Such visual signals help lizards avoid direct confrontation.
The Anatomy of Throat Expansion
Lizards expand their throats using a specialized anatomical structure known as the hyoid apparatus. This complex framework of bones and cartilage, located in the neck, supports the tongue and soft tissues of the throat. In species with prominent throat expansion, such as anoles, the hyoid apparatus is adapted for this function.
A key component is the dewlap, an extendable flap of skin typically folded beneath the throat. Muscles connected to the hyoid bone, particularly the M. ceratohyoideus, contract to pull the hyoid apparatus forward and downward. This movement causes the dewlap to unfurl and stretch out, revealing its vivid coloration. The elasticity of the skin allows the dewlap to retract back to its resting position when these muscles relax.
In green anole lizards, for example, the M. ceratohyoideus muscles activate, causing the hyoid apparatus to extend forward. This action unfurls the dewlap, creating a prominent display. This muscular and skeletal coordination enables the rapid throat expansion observed in many lizard species.
Beyond Display: Other Functions
While social communication is a primary reason for throat expansion, this behavior also serves physiological roles, particularly in respiration and thermoregulation. One function is “gular pumping” or “gular fluttering,” where lizards rapidly move the floor of their mouth and throat. This action helps circulate air over moist membranes, facilitating evaporative cooling.
This evaporative cooling is important for ectothermic lizards, which rely on external sources to regulate their body temperature. When ambient temperatures become too high, gular fluttering allows them to release excess heat. The thin membranes in the throat and mouth, rich in blood vessels, act like an internal radiator, lowering the lizard’s core temperature and preventing overheating.
Gular pumping also assists respiration, particularly during high activity or stress. Some species, like monitor lizards, utilize a positive pressure gular pump to push air into their lungs, supplementing their primary breathing mechanism. This “accessory ventilatory pump” helps maintain oxygen intake when other respiratory muscles are constrained during locomotion. This diverse range of functions highlights the adaptability of throat expansion beyond visual signaling.