A leopard gecko.
Gecko lizards occasionally puff out their neck pouches when interacting with each other. They engage in gular--or throat--expansion for various types of displays and communication.
Threat Displays
Many geckos swell their throats as part of aggressive displays. Depending on the species, these displays may involve a series of rapid neck-pouch extensions and retractions, according to a December 1990 article in the "Journal of Herpetology" and combinations of gular expansion with intimidating stances, nudges or bites, according to a report in the January 1943 issue of "Physiological Zoology"
Significance
The reasons for intimidating gular expansion and related displays are not always clear. They may involve establishing territory at a distance, preludes to fights or even provoked responses to homosexual mating attempts--a common cause of fighting between males.
Courtship
Many geckos engage in visual courtship displays that include puffing out the neck pouch--some species show off their colors this way, according to a 1977 article in "American Zoologist." Depending on the species, mating rituals might resemble or greatly differ from threats that also involve gular expansion. In the April 1978 "Journal of Herpetology," Benjamin Dial describes courtship displays that combine gular expansion with tongue flicking and other behavior.
Considerations
A green anole (not a gecko), with its dewlap extended.
When not puffed out, the neck pouches of geckos are not particularly noticeable. Geckos do not have the dewlaps--hanging flaps or dramatically extendable fans under the neck or chin--that are characteristic of some other lizards, such as iguanas, anoles and bearded dragons.
Features
Some geckos, such as mourning geckos, day geckos and tokay geckos, accumulate calcium in the endolymphatic sacs on the sides of their neck--behind the ears--which can cause the sacs to bulge noticeably. According to a December 1989 article in the "Journal of Herpetology," it is most likely that mature females use this calcium storage to help regulate egg development.
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