Hormonal control of polymorphic and sexually dimorphic coloration in the lizard Sceloporus undulatus erythrocheilus.

This study investigated the influence of sex steroids on the expression of seasonally labile and sexually dimorphic coloration in the red-lipped plateau lizard. The responses of ventral blue and polymorphic facial coloration to exogenous steroid administration were assessed. Though facial color is usually dimorphic in nature, males and females did not differ in the degree to which they expressed facial coloration following administration of testosterone (T). Both sexes developed significantly more ventral blue coloration than controls, but a fundamental dimorphism in intensity, favoring males, was maintained throughout the experiment. These results indicate that facial coloration is under activational influence of T. The ventral blue coloration is probably organized at sexual maturation, thus manifesting the more vivid expression in males. Males of this subspecies are polymorphic for facial coloration. Administration of T did not cause any lizards to change hue, whether their color morph was yellow or orange or lacked the facial pigments altogether. The difference among color morphs is probably not controlled by differences in circulating steroid concentrations and is hypothesized to be under genetic control.