AsianScientist (Jun. 16, 2016) – Bearded dragons are able to partition color change to specific body parts, depending on whether they are responding to temperature or communicating with other lizards, a new study has found.
The findings, published in Proceedings of the Royal Society B, revealed that color change in the neck area was linked to social interactions with other bearded dragons. But by changing the color of their backs to a darker shade in cool weather, the lizards were predicted to save approximately 85 hours of basking time during the energy-intensive breeding season.
Many lizards use color change for camouflage, communication and regulating body temperature. In the present study, the researchers wanted to understand how an animal might accommodate all of these different functions at once.
“The ideal internal body temperature for a bearded dragon lizard is 35°C. In order to maintain this temperature, a bearded dragon can change its back to a light yellow color when it is hot to a dark brown color when it is cool,” said Ms. Kathleen Smith, a PhD student from the University of Melbourne who led the research.
Twelve wild-caught bearded dragons (Pogona vitticeps) were observed at different temperatures and during social interactions in the breeding season in northern Victoria, Australia.
Interestingly, the lizards’ chest and beard do not change color in response to temperature, but change dramatically from cream to jet black during social interactions, accompanied by head-bobs and push-ups.
“Our results suggest that a bearded dragon lizard can balance all of its color change requirements by only changing color on the back for regulating temperature (which appears to be beneficial as it is exposed to the sun), and only changing the beard/chest color for social communication (which is the region displayed to other lizards),” she said.
Smith added that the lizards also changed to dark colors very quickly, indicating that this may be an important adaptation for rapidly-warming body temperatures.
The team predicted that the dark color change would allow more of the sun’s energy to enter the lizard’s body and warm it, so they studied the absorption and reflectivity of the bearded dragon’s skin.
The bearded dragons were photographed during exposure to temperatures of 15°C or 40°C, and the levels of light reflected from the lizard’s skin were recorded to collect the energy-rich wavelengths in the UV-visible and near infrared range (700-2,600 nm).
The spectrum of light was analyzed and then incorporated into a computer program that modeled lizard behavior at different temperatures.
“By changing to a darker color in cooler temperatures, the bearded dragons reflected much less light than the paler-colored lizards, at 8 and 23 percent reflectivity respectively,” said Professor John Endler from Deakin University, who carried out the analysis.
“The darker lizards would heat up to their active state an average 22 minutes earlier, thereby allowing them to also move away from predators sooner.”
Endler’s modeling predicted that the lizards with a darker color only on their backs could save approximately 85 hours of basking time needed to reach active body temperatures during the breeding season.
The article can be found at: Smith et al. (2016) Colour Change on Different Body Regions Provides Thermal and Signalling Advantages in Bearded Dragon Lizards.
Source: University of Melbourne; Photo: Mariposa Veterinary Wellness Center/Flickr/CC.
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