Steroid levels sand gravid coloration in Crotaphytus collaris.

Abstract

Progesterone and testosterone were measured by radioimmunoassay in serum samples taken from female Crotaphytus collaris. Data indicate that progesterone levels are higher than testosterone in gravid colored females, even though levels for both hormones were unexpectedly low. In specimens exhibiting orange-red coloration, the serum concentrations of testosterone were 0.046 ng/ml and 0.014 ng/ml. Other testosterone concentrations were low and unreliable. Other specimens with orange-red coloration had a mean serum concentration of progesterone of 2.07 ng/ml + 0.75. It was hypothesized that increases and decreases of gravid color intensity would accompany increases and decreases in the steroid levels. Gravid coloration was analyzed and then compared to the steroid levels. Similar patterns between gravid color intensities and testosterone levels were evident in two specimens. However, no final conclusion can be drawn because of inconclusive data. Data comparing gravid coloration and progesterone levels were also inconclusive.