Chameleons communicate with complex colour changes during contests: different body regions convey different information

Abstract

Many animals display static coloration (e.g. of feathers or fur) that can serve as a reliable sexual or social signal, but the communication function of rapidly changing colours (as in chameleons and cephalopods) is poorly understood. We used recently developed photographic and mathematical modelling tools to examine how rapid colour changes of veiled chameleons Chamaeleo calyptratus predict aggressive behaviour during male-male competitions. Males that achieved brighter stripe coloration were more likely to approach their opponent, and those that attained brighter head coloration were more likely to win fights; speed of head colour change was also an important predictor of contest outcome. This correlative study represents the first quantification of rapid colour change using organism-specific visual models and provides evidence that the rate of colour change, in addition to maximum display coloration, can be an important component of communication. Interestingly, the body and head locations of the relevant colour signals map onto the behavioural displays given during specific contest stages, with lateral displays from a distance followed by directed, head-on approaches prior to combat, suggesting that different colour change signals may evolve to communicate different information (motivation and fighting ability, respectively).

Keywords: Chamaeleo calyptratus; agonistic signalling; colour signals; combat; communication; physiological colour change.

Figure 1.

Colour patches measured during male–male competition between veiled chameleons. (a,b) Interindividual variation in location of colour patches can be seen by comparing the location of colour patches in (a) to those in (b). Because exact locations of colour patches varied among individuals, we focused on similarly located colour patches of equivalent pigmentary and structural makeup. Descriptions of colour patches and relevant principal component loadings are located in the electronic supplementary material, table S4.

Figure 2.

Explanatory variables associated with escalating and winning contests. Multi-model averaging indicates that average maximum stripe brightness (principal component, PC) best explains the likelihood of (a,c) a chameleon approaching his opponent and (b,d) that average maximum head brightness (PC) best explains the likelihood of a chameleon winning a fight. (a,b) Bar length is proportional to RI values of variables predicting (a) likelihood of approaching an opponent or (b) likelihood of winning an aggressive interaction, with green bars indicating RI values greater than 0.60 and orange bars indicating RI values greater than 0.30. Average parameter estimates of regression coefficients (β) were obtained using multi-model-averaging approaches and dots indicate parameter estimates with absolute values less than 0.005. (c) Regression of chameleon stripe brightness and approach ability calculated across trials. Average stripe brightness values represent PC scores, all of which had negative loadings of maximum brightness values (chameleons with brighter bodies had negative PC scores). (d) Regression of head brightness on fighting ability. Colour-metric predictor variables in (a–d) represent principal component scores from multiple colour patches within a region (see electronic supplementary material, table S4). Abilities plotted in (c,d) represent Bradley–Terry ‘ability’ scores.