The truth about chameleons

Everyone knows chameleons can change colour, but why do they do it? Suppose you were given these three options: (a) to blend in with their surroundings, (b) to get a mate, or (c) to impress humans.

For most chameleons, changing colour is all about obtaining a mate

I think most people would instinctively lump for the camouflage option. But the real answer is (b).

It's not a hard-and-fast rule: there is some evidence that the colourful antics of chameleons can be a disguise. For instance, the dwarf chameleon Bradypodion taeniabronchum seems to match its surroundings more closely when confronted with a predator with better colour vision.

For most chameleons, however, changing colour is all about obtaining a mate. 

In their natural environment, most chameleons blend in with their surroundings pretty well, says ecologist Kristopher Karsten of California Lutheran University in Thousand Oaks.

A chameleon in the midst of a colour change probably isn't so much acting shifty as it is sexually aroused

So when they change colour, they tend to make themselves more conspicuous. "They get away from the cryptic," says Karsten.

Competing males will often battle it out with a colour-change face-off. Both males and females will try to impress with a dermal flush.

So when we use the word "chameleon" to describe people who are a bit fickle or changeable, we are getting it wrong. A chameleon in the midst of a colour change probably isn't so much acting shifty as it is sexually aroused.

The colour-change process doesn't work the way you might expect it to either.

Most of us would assume it is achieved by some kind of dyes or pigments. But a study published in March 2015 suggests that the chromatic shenanigans have nothing to do with chemistry at all.

The chameleons were able to split their gaze, each eye independently tracking a different blob

Instead, it turns out there are two superimposed layers of nanocrystals embedded within the chameleon's cells. By altering the positions of these crystals, the chameleon can reflect different shades of colour.

It's not just about how chameleons look. They are also unusually good at using their eyes.

In a neat study published in July 2015, zoologists presented chameleons with two animated objects that buzzed around a computer screen. The chameleons were able to split their gaze, each eye independently tracking a different blob.

Eventually, the reptiles seemed to make a choice, both eyes locking onto the same target. By switching to stereoscopic vision, they could do a better job of judging how away the objects were – and thus how far to shoot out their tongues.

Talking of tongues, a chameleon's tongue is as worthy of celebration as its polychromatic skin.

There is a lot that we still don't know about chameleons

A 2004 study used slow-motion footage to show that a chameleon tongue is fired by an ingenious elastic catapult-like mechanism.

The researchers found that the tongue of a giant one-horned chameleon reached a top speed of 6 m/s. At that rate, it would slam into a prey item 1.5 body lengths away in less than a tenth of a second.

All that said, there is a lot that we still don't know about chameleons.

At the latest count published in 2015, taxonomists recognized more than 200 species. Around half of these live in Madagascar.

I could find adults but very few of them, and I couldn't find any juveniles

That includes the world's smallest chameleon, Brookesia micra, which was discovered in 2012 on a tiny island called Nosy Hara – the same island, incidentally, where a new population of dwarf lemurs was recently found. Males of B. micra appear to be less than 1.6 cm from snout to anus.

Other chameleons have evolved distinctly weird lifestyles, as Karsten discovered during his PhD.

During his first field season in western Madagascar in 2003, he struggled to get data on one species: Labord's chameleon (Furcifer labordi).

"I could find adults but very few of them, and I couldn't find any juveniles or any smaller chameleons," says Karsten. "I can't tell you how depressed I was. I felt like such a failure."

So in his second year, Karsten went out to Madagascar a little earlier.

"I found a lot more of them but they were a lot smaller," he says. That gave him an idea: "Maybe they are an annual species."

It spends more of the year as an egg than hatched out

Labord's chameleon, it turns out,has one of the shortest life cycles of any land-dwelling backboned animal.

Eggs are laid around February and sit out the next eight months in a state of suspended development. When the rains come, around October, the hatchlings emerge, mature in a couple of months, reproduce and then die.

"It spends more of the year as an egg than hatched out," says Karsten. That sort of thing is common in insects, which often spend months as a larva or caterpillar then have a brief adulthood, but among backboned animals it is bizarre.

/By BBC/