En garde!: Two male knysna dwarf chameleons Bradypodion damaranum in a stand-off. The male on the left is showing dominant colouration (green) whilst the male on the right is showing submissive colouration (dark brown).
Credit: Devi Stuart-Fox and Adnan Moussalli
SYDNEY: Everyone knows that chameleons change colour to expertly camouflage themselves in the environment… or do they? New research turns that idea on its head with evidence that the ability evolved for flashy social displays instead.
The findings, published in the journal PLoS Biology give us new insights into myriad of ways animals communicate.
"Chameleons are famous for their ability to change colour and most people think that this is so that they can match different backgrounds," said Devi Stuart-Fox, lead author of the study and expert on animal behaviour at the University of Melbourne in Australia. "Not many people think that the evolution of colour change might be driven by the need to have conspicuous signals that can be quickly flashed to another chameleon."
Rainbow of variation
The evolution of colour change has occurred in many groups of animals, the more well-known being cephalopods (octopuses and squids) and chameleons. Chameleons are famous for their rapid ability to change colour, and the range of colours varies between species.
This variation between the colour range of different species allowed Stuart-Fox and her co-worker Adnan Moussalli, of Museum Victoria in Melbourne, to test a hypothesis about why the ability evolved.
They argued that chameleons that live in more diverse environments would be expected to have more variation in their colour changing ability if the ability had evolved to camouflage them. To test this they pitted males of 21 species against each other in colour changing 'duels' where they sat two chameleons opposite one another on a branch and measured the amount of variation in colour.
"If chameleons evolved colour change so that they could match a variety of backgrounds, then we would expect a relationship between a species capacity for colour change and the variation of backgrounds that chameleons match in their environment. However we found no evidence for this," said Stuart-Fox.
Aggression and seduction
Instead the pair compared the evolutionary relationships of the species to find evidence that the ability evolved to allow the reptiles to aggressively display to competitors and seduce mates. Though they now use the trick for camouflage too, this wasn't its primary use, they said.
Males display a vivid colouration to court females and to signal dominance to other males, however when a male chameleon loses a contest or is rejected by a female, he displays submissive, dull colouration, said Stuart-Fox. Because these conspicuous signals are only briefly displayed during these times, the chameleons can be hidden from predators the remainder of the time.
"The study solves an interesting puzzle about why colour change evolved and why some species show much greater colour change than others," she added.
"This study shows with crystal clarity that there isn't any strong relationship between an ability to change colour and your camouflage against the environment," commented reptile ecologist Rick Shine, from the University of Sydney. "It is, in fact, driven by social display and highlights the advantages of showing up very clearly when trying to communicate with neighbouring chameleons."
