Sex differences in plasma corticosterone levels in alligator (Alligator mississippiensis) embryos

Abstract

The sex of alligator embryos is determined by incubation temperature. Females are produced at temperatures between 29°C and 31°C and males at 33°C. As part of an ongoing study on the hormonal basis of sex determination in the alligator, we collected plasma and urogenital tissue from alligator embryos incubated at 30°C (females) and 33°C (males). Progesterone and corticosterone were determined by radioimmunoassay (RIA) in both plasma and urogenital tissue in embryos prior to the temperature-sensitive period (stage 17 in females and stage 20 in males) and at weekly intervals throughout the remainder of development until hatch. Corticosterone began increasing by stage 25 in both tissue and plasma of both sexes and continued to rise until hatching. Plasma progesterone on the other hand was very low throughout the second half of incubation in both sexes. Tissue levels of progesterone were low early in development and increased later in development. Plasma corticosterone values were significantly higher in female than in male embryos in the last week of incubation. However, by 3 weeks after hatch, plasma corticosterone levels had decreased significantly in both sexes and were not significantly different from one another. Plasma estradiol was significantly higher in female hatchlings than in male hatchlings. J. Exp. Zool. 280:238–244, 1998. © 1998 Wiley-Liss, Inc.