Steroid correlates of multiple color traits in the spiny lizard, Sceloporus pyrocephalus

Conspicuous coloration in females is less well studied compared to that in males. Adult female Mexican boulder spiny lizards (Sceloporus pyrocephalus) have conspicuously colored throat, or gular, regions, ranging from red to yellow, while adult males only weakly express such color in their gular region. Both sexes have dark blue-black gular stripes and venter stripes. Understanding proximate mechanisms underlying trait expression can aid in understanding trait function. To characterize the proximate mechanisms potentially influencing color variation among field-captured male and female S. pyrocephalus, we quantified three aspects of color (hue, saturation, brightness) for three body locations (gular region, gular stripes, venter stripes) and then assessed how color was related to reproductive state and concentrations of the plasma steroid hormones testosterone (T) and corticosterone (CORT) in males and T, CORT, and 17-beta estradiol (E-2) in females. Testes volume was not related to variation in color or in hormones, perhaps because most males were in peak reproductive condition. Large vitellogenic follicles as opposed to oviductal eggs were associated with higher E-2 in females. Males with more dull gular stripes and females with dull venter stripes had significantly higher CORT. Females with red gular regions and pale grey gular stripes had higher T and E-2 concentrations compared to females with a more yellow gular region and darker gular stripes. Thus, gular region color in females could communicate reproductive state; dull gular stripes in males and dull venter stripes in females could communicate stress status.