Female Breeding Coloration
In all species of the family Crotaphytidae (Gambelia and Crotaphytus), females develop bright red or orange pigmentation on the sides of the head, lateral torso, and ventral surface of the tail during the breeding season. In older literature, the term gravid coloration was used to describe this type of coloration, but in most species, the color actually develops before the female is gravid (pregnant).This coloration develops as hormone levels (specifically progesterone and estrogen) increase in females during the breeding season. Once the color has developed, it remains until the female deposits her clutch of eggs. It is thought that female breeding coloration plays a role in mate choice decisions, either deterring or attracting males. In some species, such as Crotaphytus collaris, breeding coloration is a signal that stimulates courtship (Baird, 2004). Yet in other iguanian lizard species, such as Holbrookia maculata, the intensity of the coloration allows males to monitor when females become receptive (Hager, 2001). Generally, the role of this bright coloration is poorly understood in most lizard species.
Interestingly, subadult male collared lizards develop a similar color pattern that resembles female breeding coloration. It was thought that this color develops as a mechanism to mimic females and thus reduce male aggression. But studies have shown that males are equally aggressive to subadults with and without coloration (Husak et al., 2004).
Whatever the role of female breeding coloration (or its mimic in juvenile males), it is present when the lizard is most vulnerable (while gravid or when still a subadult), and makes these otherwise inconspicuous lizards more visible to predators. So the signal communicated through these bright markings must have important fitness benefits.
Crotaphytus vestigium -- Baja Black-collared Lizard
Baird, T. A. 2004. Reproductive coloration in female collared lizards, Crotaphytus collaris, stimulates courtship by males. Herpetologica 60:337-348.
Fox, S. F., J. K. McCoy, and T. A. Baird (eds.). 2003. Lizard Social Behavior. Johns Hopkins Univ. Press, Baltimore, MD.
Hager, S. B. 2001. The role of nuptial coloration in female Holbrookia maculata: evidence for a dual signaling system. Journal of Herpetology 25:624-632.
Husak, J. F., J. K. McCoy, S. F. Fox, and T. A. Baird. 2004. Is coloration of juvenile male collared lizards (Crotaphytus collaris) female mimicry? An experimental test. Journal of Herpetology 38:156-160.