The evolution of flamboyant traits in animals is typically attributed to the selective force of sexual selection. However, natural selection can constrain the degree of elaboration of such traits. Therefore, animal signals reflect a balance between natural and sexual selection. I examined the role of these forces in the maintenance of a complex visual signal: dynamic colour change. Males of the Indian rock agama (Psammophilus dorsalis) exhibit rapid dynamic colour changes on their dorsal and lateral body regions during social interactions. The costs, benefits and adaptive significance of this relatively rare signal type is yet unknown.

Using a combination of visual modelling and field experiments, I first examined the predation risk on social colours and found that the courtship signal of males is costlier than the aggression signal. I then tested whether male colours expressed during aggression convey information about individual physiology and performance measures. Apart from a negative association between testosterone levels and the yellow colour expressed during aggression, body size and bite force were correlated, suggesting that body size could be an honest predictor of fighting ability. In the third chapter, I examined differences in health parameters of males and females that occupy dramatically different habitats as a consequence of urbanization. My results suggest that lizards in urban areas appear to have shifted their innate physiology in order to cope with urban stressors. Finally, I examined the response of receivers to different components of the male colour signals by assessing attention paid by conspecific receivers to each signal component independently and together. Both males and females responded equally to all male social colours although females showed difference in response to achromatic signals. Overall, I conclude that dynamic colour change may have evolved in this species to actively balance the costs of predation risk with the benefits of social signalling.