Communicating In Colour

There are more than 160 known species of chameleons. The main distribution is in

Africa and Madagascar, and other tropical regions, although some species are also

found in parts of southern Europe and Asia. There are introduced populations in

Hawaii and probably in California and Florida too.

New species are still discovered quite frequently. Dr. Andrew Marshall, a

conservationist from York University, was surveying monkeys in Tanzania.

Accidently, he stumbled across a twig snake in the Magombera forest, which,

frightened, coughed up a chameleon and fled. Though a colleague persuaded him

not to touch it because of the venom’s risk, Marshall suspected it might be a new

species and took a photograph to send to colleagues, who confirmed his suspicions.

Kinyongia Magombera, literally “the chameleon from Magombera,” is the result, and

the fact it was not easy to identify is precisely what made it unique. The most

remarkable features of chameleons are their ability to change colour and ability

rivalled only by cuttlefish and octopi in the animal kingdom. Because of this, colour is

not the best thing for telling chameleons apart, and different species are usually

identified based on the patterning and shape of the head, and the arrangement of

scales. In this case, it was the bulge of scales on the chameleon’s nose.

Chameleons can use colour for both communication and camouflage by switching

from bright, showy colours to the exact colour of a twig within seconds. They show

an extraordinary range of colours, from nearly black to bright blues, oranges, pinks,

and greens, even several at once. A popular misconception is that chameleons can

match whatever background they are placed on, whether a chequered red and

yellow shirt or a Smartie box. But each species has a characteristic set of cells

containing pigment distributed over their bodies in a specific pattern, which

determines the range of colours and patterns they can show. To the great

disappointment of many children, placing a chameleon on a Smartie box generally

results in a stressed, confused, dark grey or mottled chameleon.

Chameleons are visual animals with excellent eyesight, and they communicate with

colour. When two male dwarf chameleons encounter each other, each shows its

brightest colours. They puff out their throats and present themselves side-on with

their bodies flattened to appear as large as possible and show off their colours. This

enables them to assess each other from a distance. If one is clearly superior, the

other quickly changes to submissive colouration, usually a dull combination of greys

or browns. If the opponents are closely matched and both maintain their bright

colours, the contest can escalate to physical fighting and jaw-locking, each trying to

push each other along the branch in a contest of strength. Eventually, the loser will

signal his defeat with submissive colouration.

Females also have aggressive displays used to repel male attempts at courtship.

When courting a female, males display the same bright colours that they use during

contests. Most of the time, females are unreceptive and aggressively reject males by

displaying a contrasting light and dark colour pattern, with their mouths open and

moving their bodies rapidly from side to side. If the male continues to court a female,

she often chases and bites him until he retreats. The range of colour-change during

female displays, although impressive, is not as great as that shown by males.

Many people assume that colour change evolved to enable chameleons to match a

greater variety of backgrounds in their environment. If this was the case, then

chameleons’ ability to change colours should be associated with the range of

background colours in the chameleon’s habitat, but there is no evidence for such a

pattern. For example, forest habitats might have a greater range of brown and green

background colours than grasslands, so forest-dwelling species might be expected

to have higher colour change powers. Instead, the males whose display colours are

the most eye-catching, show the greatest colour change.

Their displays are composed of colours that contrast highly with each other and the

background vegetation. This suggests that the species that evolved the most

impressive capacities for colour change did so to enable them to intimidate rivals or

attract mates rather than to facilitate camouflage.

How do we know that chameleon display colours are eye-catching to another

chameleon – or, for that matter, to a predatory bird? Getting a view from the

perspective of chameleons or their bird predators requires information on the

chameleon’s or bird’s visual system and how their brains might process visual

information. This is because the perceived colours of an object depend on the brain’s

wiring as on the physical properties of the object itself. Luckily, recent scientific

advances have made it possible to obtain such measurements in the field, and

information on visual systems of a variety of animals is becoming increasingly

available.

The spectacular diversity of colours and ornaments in nature has inspired biologists

for centuries. But if we want to understand the function and evolution of animal

colour patterns, we need to know how they are perceived by the animals themselves

– or their predators. After all, camouflage and conspicuousness are in the eye of the

beholder