Orange ornamentation increases sex-specific conspicuousness of juvenile males to conspecifics and predators

Many animal species have evolved striking colour patterns that attract the opposite sex and intimidate rivals. Although conspicuous coloration is usually restricted to adults in the context of reproduction, this is not always the case. Juvenile collared lizards (Crotaphytus collaris) are sexually dichromatic, wherein males exhibit ‘dorsolateral bars’ that are bright orange and showy, whereas females are light tan and inconspicuous. Given that adult male collared lizards suffer increased predation because of bright adult coloration, we hypothesized that juvenile males might also be more detectable to predators owing to the conspicuousness of their dorsolateral bars. To test this hypothesis, we measured the reflectance of the dorsolateral bars, non-bar background body regions, and the rocky habitat in which the lizards live. We modelled the vision of our study species and its dominant predators to quantify and compare statistically the contrasts of male and female dorsolateral bars against the natural rock background. We also calculated lizard survivorship over a 4 year study period. We found that male orange bars exhibited significantly higher chromatic contrast, but significantly lower achromatic contrast, than female bars when perceived through all visual models. However, the dorsolateral background colour of juvenile males and females did not differ significantly in chromatic or achromatic contrast from rocks in any visual model. Female lizards survived better than male lizards to the yearling (reproductive) stage. Our findings indicate that juvenile male bars are conspicuous both to conspecifics and to predators and that the bars probably increase predation on juvenile males.