Species: The Jamaican Gray anole (Anolis lineatopus)
Habitat: Shaded forests of Jamaica
Luminous lizard lotharios ahoy! In the dark undergrowth of the forest, it鈥檚 not easy to be seen. Male Anolis lizards use colourful throat fans, called dewlaps, to woo females as well as ward off rivals and predators. But one species has a neat trick to make itself stand out even more 鈥� it uses an optical illusion to make its dewlap appear to glow.
The dewlaps are translucent, which means they can transmit as well as reflect light. However, because most objects in the lizards鈥� environment 鈥� such as rocks and tree trunks 鈥� simply reflect light, our eyes 鈥渆xpect鈥� them all to appear relatively dull. By transmitting light from the background, the dewlap tricks our eyes 鈥� and the eyes of other lizards 鈥� into thinking it is actually a light source, says of Union College in Schenectady, New York, who has studied the lizards for years.
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Fleishman鈥檚 team was curious to find out why the trick evolved 鈥� was the glowing dewlap a way to increase contrast with darker backgrounds or a way to make its colour clearer?
To explore the issue, Fleishman鈥檚 team examined the photoreceptors in the lizard鈥檚 eyes to work out how they would view the dewlaps. They found that the glow did not create more contrast with the background, which naturally contains other bright spots 鈥� where a patch of sunlight passes through the vegetation, for instance. But the glow did significantly reduce the visual overlap, as the lizard鈥檚 eyes would experience it, between the throat fans and the colours of natural backgrounds.
The glowing dewlap may be more common than we think. Only a few of some 400 species of Anolis lizards are known to carry the trait, but Fleishman has seen photos suggesting other species鈥� dewlaps might glow too.
鈥淢y guess is that the phenomenon will turn out to be widespread once people start looking, but very few people have looked,鈥� he says.
Journal reference: Functional Ecology, DOI:
