The word "chameleon" is almost synonymous with camouflage. But the chameleon's famed ability to change colors may be more about sticking out than blending in: A new study in PLoS Biology suggests color change is a way for the lizards to send each other signals related to mating - but to do so quickly, so as not to attract predators.

Devi Stuart-Fox and Adnan Moussalli at the University of Melbourne examined color change in pairs of adult male chameleons of several species native to southern Africa. They looked at how color change correlated with factors such as color variation in the animals' background (predicted to be high if the animals are camouflaging) and the visibility of dominance signals the two males exchanged in their face-off (predicted to be high if the animals are signaling). They also modeled how color changes would be perceived by the chameleons' visual system and that of one of their key predators, birds.

"We found that the species that show the greatest capacity for chromatic color change have display signals that are highly conspicuous" to members of the species, the authors write. At the same time, color changes did not appear to be related to the variation in their environment, or to their visibility to avian predators. The researchers note that color change in reptiles that are sister families to chameleons does appear to be driven by camouflage. Perhaps camouflage was the original evolutionary driver, they suggest, but some types of chameleons then evolved the use of color changes as a signaling strategy.

The study "is a substantial contribution to our understanding of how social behavior can influence the evolution of physical traits," Jackie Grant, a wildlife ecologist at Michigan Technical University who was not associated with the work, wrote in an Email to The Scientist. It demonstrates that "the chameleons have taken advantage of the very brief nature of their communications to each other to evolve complex signals based on color change," she added.

Grant also noted that the study was unusual in that it took into account how color change might be viewed by a predator. "One of the things they do mention is that they probably should consider other predators such as snakes," she said, but the snake visual system would have been more difficult to model because it is less well understood than that of birds.