“Color change for thermoregulation versus camouflage in free-ranging lizards”

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Kathleen R. Smith, Viviana Cadena, John A. Endler, Michael R. Kearney, Warren P. Porter, and Devi Stuart-Fox

Bearded dragon lizards use color change to improve both thermoregulation and camouflage in the wild

Bearded dragons (Pogona vitticeps) use many different habitats, and colors to help them regulate body temperature in the wild. Here, this bearded dragon is being a true ‘lounge lizard’ by cooling down on some branches on a hot spring afternoon. Photographed in Walpeup, Australia.
(Credit: Kathleen R. Smith)

Why change color? Octopuses and chameleons are famous for their ability to rapidly change color, but they are not the only ones. Many frogs, fish and lizards, such as the Australian bearded dragon lizard, share this remarkable ability. Color change could give animals several advantages, such as the abilities to match different backgrounds, to regulate body temperature by becoming darker when cold to absorb more energy from the sun (especially for cold-blooded terrestrial animals), or both. But what do animals prioritize in the wild? Until now, this question has remained unanswered because of the challenges of measuring rapid color change in free-ranging animals.

Color change in an individual of the inland bearded dragon lizard (Pogona vitticeps).
(Credit: Adam Elliot)

By radio-tracking individual bearded dragon lizards in the wild and measuring their color from photos, a team of researchers from The University of Melbourne, Deakin University and The University of Wisconsin Madison has showed that these lizards change color to match their backgrounds almost perfectly, thereby protecting them from detection by predators. But they also change color depending on their body temperature. When they are cold in the morning, the lizards become dark to enable them to warm up more quickly so they can reach the body temperatures needed to forage, defend territories from rivals, and find mates. Once lizards are warm and active, the study suggests that bearded dragons use color change more for camouflage and communication than temperature regulation, because they can regulate temperature in other ways, like shuttling in and out of shade.

The researchers tested the possibility that lizards used more sophisticated ways to maximize the benefits of color change. For example, lizards might get the best of both worlds by choosing dark backgrounds when cold (so they are both camouflaged and get the benefits of faster warming), or even modifying how their skin reflects near-infrared wavelengths of sunlight, but found no evidence for this. But thanks to this study, we now have evidence for several simultaneous benefits of being able to rapidly change color. Read the Article