Colour change evolved for communication
The two primary explanations for the evolution of colour change are that it evolved to enable camouflage against a variety of backgrounds; or that it evolved to allow animals to use highly conspicuous social signals (while remaining camouflaged at other times).
We tested these alternative explanations in a comparative study of southern African dwarf chameleons (Bradypodion spp.). We conducted field-based behavioural trials on 21 lineages of dwarf chameleon and measured their colour change in response to predators and other chameleons. Chameleons showed the greatest colour change during “duels” between males. If a male was challenged by another male they both began by showing their brightest colours – until one conceded defeat and changed to a submissive, dark, ‘don’t beat me up colour’. We measured colour with a spectrometer, which measures both the UV and visual colour range, and combined this with information on the chameleon visual system to model chameleon colour perception.
Our results indicated that the evolutionary changes in the capacity for colour change in dwarf chameleons are associated with increasingly conspicuous signals used in male contests. By contrast, the degree of colour change among species was unrelated to the habitat they occupied or variety of background colours. Our results suggested that selection for conspicuous social signals drives the evolution of colour change in dwarf chameleons.
To learn more, read the full paper:
Stuart-Fox, D. and Moussalli, A. 2008. Selection for social signalling drives the evolution of chameleon colour change. PLoS Biology 6: e25. PDF
Or read the media coverage of the study:
Calculating chameleons – BBC Wildlife Magazine (December 2009)
Conspicuous social signaling drives evolution of chameleon color change – Science Daily (3 February 2008)
Chameleon colour not to blend in – BBC News (29 January 2008)
New theory on colour-changing chameleons – Cosmos Magazine (29 January 2008)
There’s no hiding this camoflage – Science (29 January 2008)
Chameleons evolved color changing to communicate – National Geographic (28 January 2008)
Photo credit: Adnan Moussalli & Devi Stuart-Fox