科学美国人60秒 SSS Color-Changing Skin Aids Climate Control and Communication（在线收听）

Various animals evolved coloration that keeps them hidden. A jaguar's patterns help it slink undetected across the sun-dappled rainforest floor. The mottled pigmentation on the wings of some let them rest on tree bark undisturbed. And then there are animals that can quickly change their appearance—for example, the Central Bearded Dragon.

This two-foot-long lizard lives in the more arid parts of Australia. 

"They can change color really quickly, just in a matter of seconds or minutes.”

University of Melbourne biologist Katie Smith.

“And they do this by moving pigments within specialized skin cells called chromatophores." 

Bearded dragons modify their colors for camouflage, or to maintain their body temperature, or to communicate with other dragons. Smith wanted to know how they meet all those needs with the same tool kit. 

So she and her team rounded up twelve bearded dragons and put them through a series of tests before releasing them back into the wild. They found that when the dragons want to communicate with other members of their species, they change the colors on their neck. 

"This is actually one of the reasons they're called bearded dragons—because they look like they have a really serious five o'clock shadow."

Changes to their backs were for temperature regulation. Shifting to yellow lets them to cool off during extreme heat, while darker greys allow them to soak up more heat during cooler weather. 

"They actually save about, on average, 22 minutes a day at the darker colors than the lighter colors. That's about 85 hours throughout the whole year." 

Eighty-five hours a year NOT spent out in the open and exposed to potential predators. The results were published in the Proceedings of the Royal Society: B. [Kathleen R. Smith, Viviana Cadena, John A. Endler, Warren P. Porter, Michael R. Kearney, & Devi Stuart-Fox. Colour change on different body regions provides thermal and signalling advantages in bearded dragon lizards.]

The lizards can clearly control each part of their body separately, resulting in an efficient system. Temperature regulation involves the back, which is facing the sun. Social signaling uses the neck, easily visible to another lizard they’re faced off with. 

The researchers' next task is to see what happens when the lizards have to deal with simultaneous but conflicting coloration requirements—situations that could give a bearded dragon a close shave. 

—Jason G. Goldman