Skin that changes color according to one’s emotional status may be the stuff of human nightmares; for chameleons, though, it’s essential to survival. The lizards’ hue-changing skin, for one thing, functions as a kind of external thermostat, allowing the creatures to regulate their body temperatures: Dark skin absorbs more heat than pale. But changeable skin also allows the animals to communicate with each other. Males become bright when they’re attempting to express their dominance; they become dark during aggressive encounters with those who would question that dominance. Females use their skin color to signal a willingness—or lack of willingness—to mate. It’s skin that doubles, essentially and a little horrifically, as a flexible mood ring. “Owners of chameleons,” Wired pointed out last year, “can learn to read their pet’s mood based on the color of its skin.”
But how, actually, do the animals carry out their skin-based semaphore? A new study from the journal Nature Communication suggests an answer. Researchers used spectroscopy to examine in detail how light and matter interact within the chameleons’ skin. Their conclusion: The color-changing takes place via crystals—iridophores, they’re called—arranged under the chameleons’ skin. The iridophores are formed from guanine, one of the building blocks of DNA, and they’re “efficiently organized” across the chameleons' skin in a triangular lattice design.