From ABC News in Science, 30 October 2014:
The charismatic Australian bearded dragon changes colour in sync with its circadian rhythm, researchers have found.
The study, published today in PLoS ONE , shows that the dragon continues to change from dark colours during the early part of the day, to light at night, even when kept in the dark for 24 hours.
The central bearded dragon (Pogona vitticeps) is one of just a few reptiles known to show rhythmical colour changes, in addition to its more spectacular mating displays and its ability to camouflage against its background.
Researchers from the University of Exeter and University of Melbourne were studying the thermal benefits of colour change in the bearded dragon, and decided to explore the cyclical nature of the dragons’ colour change.
“We have been measuring colour change across the full solar spectrum and then looking at how that affects the speed at which they heat up and cool down,” says co-author and evolutionary biologist Dr Devi Stuart-Fox, from the University of Melbourne.
Dragons are typically dark-brown in the morning, which helps them to absorb more heat to reach their active body temperature. Then, when they need to control their body temperature during the heat of the afternoon, their skin turns a light cream or orange colour, and remains that way throughout the night.
However the researchers were surprised to discover that this pattern persisted—albeit in a slightly less pronounced fashion—even when the lizards where kept in the dark for 24 hours, suggesting the colour change wasn’t just tied to light exposure. Read more.