Chameleon aggressive display change
Colour is a great cue for animals. There is no better terrestrial master of the trade of colour communication than the chameleon. Russell Ligon and Kevin McGraw chose the poorly understood area of colour change for the latest photographic and mathematical modelling techniques. Chameleo calyptratus is the veiled chameleon, found particularly in the Yemen, Saudi Arabia and the Emirate mountains, although its habitat is limited by an arboreal habit! They are quite feisty, so males take the chameleonic approach to aggression by first showing a broadside, before any faceto-face approach. This leads the stripes on the side to assume great importance in signalling, before the facial colour takes over for later confrontation.
With their fixed colour, mating or territorial displays in birds, fish and others have a local display function. Cephalopods and chameleons have far more complex change, involving many more parts of their body. This research concentrated on the maximum stripe brightness and maximum head brightness displayed by this reptile species. Also, the rate of change proved important, with the speed of head colour change determining who won aggressive encounters. Both motivation and fighting ability seem to be displayed by these males, as they limber up for vital battles.
The paper uncovers for the first time how change occurred as 2 males observe each other sideways from a distance. The escalation of conflict was predicted by the stripe display on the side of the body. Close approach enabled their own assessment of head coloration . This gives the prediction of who is going to win and lose, so the sensible male would now either stop, or escalate the aggression. Mathematical correlations provided the key evidence of the colour/behaviour connection.
This kind of signal of an outcome is rare, and very useful to this species. Hormone status and energy reserves possibly play a part in brightening the display, helping the animals to survive injury by avoiding actual action. We are genuinely looking forward to further research on this little-worked area.
Russell A. Ligon and Kevin J. McGraw are continuing their research at Arizona State University in the US, publishing today in Biology Letters of the Royal Society.