If you describe someone as a chameleon, you probably mean that they’re great at blending in, at changing their behaviour to suit different social situations. You probably don’t mean that they make their heads really bright when they’re about to get in a fight. The latter, however, would be more fitting.
Chameleons are famed for their ability to change colour, and people usually assume that this helps them to camouflage themselves from predators or prey. But in 2008, Devi Stuart-Fox and Adnan Moussalli showed that chameleons probably evolved their dynamic palettes to be social rather than secretive, to stand out rather than blend in.
The duo studied 21 species and sub-species of South African dwarf chameleons and found that those that undergo the most dramatic colour changes show stronger contrasts between different body parts, and stand out more strongly against their normal environments. It was communication not disguise that drove their capacity for colour change.
But what are they communicating? It’s possible that their messages are very sophisticated because they can change colour very quickly, and control the hues of different body parts independently. Their bodies don’t just flip between two settings. They’re dynamic living displays. And Russell Ligon and Kevin McGraw from Arizona State University have now shown that chameleons can convey different information by changing the colours of different body parts.
The duo set up duels between male veiled chameleons—a large species that grows up to two feet long, and has a reputation for being aggressive. When males meet each other, they react aggressively. They hiss, rock and curl their tails. They turn sideways and change the shape of their bodies from a narrow tube into a flat panel, filled with bright stripes and fleckles of green, turquoise, orange, yellow, lilac and charcoal.
“The changes essentially, turn the chameleon’s entire body into a billboard advertisement,” says Ligon. “The situation can escalate rather quickly. If neither chameleon backs down, they fight with full-body lunges and bites.” This usually lasts for just a few seconds, before one combatant realises he’s outmatched and backs down. Ligon and McGraw only had to intervene in one of their staged bouts, when a smaller rival pushed his luck so far that his opponent drew blood.
As the lizards squared off, the duo photographed them every four seconds, and measured the brightness and colours of 28 body parts. They also converted their photos according to the technical specifications of chameleon eyes, to see the individuals as other chameleons would see them.
They found that the brightness of the chameleons’ stripes predicted how likely they were to approach their rivals. This factor alone accounted for 71 percent of the variation in their motivation. Meanwhile, the brightness of their heads predicted their odds of actually winning their fights, and accounted for 83 percent of the variation in their fighting ability. (To a lesser extent, the speed of their colour change also says something about their combat skills.)
So, if you were a veiled chameleon facing off against a rival, pay attention to their stripe. If it becomes much brighter, they’re fixing for a fight. If their head becomes really bright, and does so quickly, they’re one tough lizard, and they’ve got a good chance of winning. And ignore the actual colours—making big jumps from one hue to another doesn’t tell you very much.
Stuart-Fox, who was not involved in the study, praised it for being the first to look at colour change as it would be perceived by actual chameleons—something that no one has done before when assessing contests.“It shows for the first time that the speed of colour change can affect contest dynamics – a discovery only possible because of the sophisticated way they quantified colour change,” he says.
Why do different body parts convey different information? “If I had to guess, I would say that these links exist because selection favoured the display of signals which could be accentuated at different, appropriate stages of an aggressive interaction,” says Ligon.
Chameleons are slow-moving, and their fights progress through a series of gradual stages. When they’re threatening each other, they face side-on, so it makes sense for their stripes to communicate their motivation for a fight. When they actually come to blows, they face head-on; again, it makes sense that their heads should signal their prowess in combat.
So far, Ligon and McGraw have found some intriguing correlations. Next, they want to start doing experiments, by controlling the changing colours of a chameleon model or robot to see how a rival reacts. Ligon also wants to know how the males use their colour-changing abilities during courtship, rather than just combat. “There’s a lot left to be done,” he says.
Reference: Ligon & McGraw. 2013. Chameleons communicate with complex colour changes during contests: different body regions convey different information. Biology Letters http://dx.doi.org/10.1098/rsbl.2013.0892