Dewlaps are colorful flaps of skin that hang off the throats of male lizards. When deployed, this expandable fan can rapidly transform a lizard from drab to fab (as you can see in the picture above). Not only does it attract females, it also repels rival males and discourages predator attacks. At least one species has taken it a step further: Under some lighting conditions, the dewlap of a Jamaican gray anole appears to glow, and vividly so.
The lighting in forests can be pretty dim. And while rocks, dirt, leaf clusters, and tree trunks might reflect light, they don’t transmit it – at least not in the way that a lampshade might. The dewlap of the Jamaican lizard Anolis lineatopus, on the other hand, is translucent, which allows it to transmit a lot of diffuse light. If a beam of sunshine strikes the back of its colorful dewlap, it’ll look like it’s emitting light. Natural selection seemed to favor the evolution of a translucent dewlap as a way of increasing the lizard’s signaling in dimly-lit shady forests. But does this translucence increase the dewlap’s contrast with the lizard’s low-lit background or does it make the colors more recognizable?
To investigate, a team led by Leo Fleishman of Union College calculated dewlap color for the lizard – with and without transmitted light – at their natural perch sites along the north shore of Jamaica near Robin’s Bay and Priory. In addition to watching undisturbed lizards for up to 10 minutes or until they displayed their dewlap, the team also examined the light-sensing photoreceptors in their eyes to see how they perceive the throat fans.
They found that the glow didn’t create more contrast with the background, New Scientist reports, but the glow did reduce the visual overlap between dewlaps and the various other colors found in their natural backdrops. At least that’s the way the lizard’s eyes would experience it.
Their findings were published online in Functional Ecology last month. Check out this New Scientist video for some spectacular dewlap displays: