SEX-DIFFERENCES IN PLASMA-CORTICOSTERONE LEVELS IN ALLIGATOR (ALLIGATOR-MISSISSIPPIENSIS) EMBRYOS

The sex of alligator embryos is determined by incubation temperature. Females are produced at temperatures between 29 degrees C and 31 degre es C and males at 33 degrees C. As part of an ongoing study on the hor monal basis of sex determination in the alligator, we collected plasma and urogenital tissue from alligator embryos incubated at 30 degrees C (females) and 33 degrees C (males). Progesterone and corticosterone were determined by radioimmunoassay (RIA) in both plasma and urogenita l tissue in embryos prior to the temperature-sensitive period (stage 1 7 in females and stage 20 in males) and at weekly intervals throughout the remainder of development until hatch. Corticosterone began increa sing by stage 25 in both tissue and plasma of both sexes and continued to rise until hatching. Plasma progesterone on the other hand was ver y low throughout the second half of incubation in both sexes. Tissue l evels of progesterone were low early in development and increased late r in development. Plasma corticosterone values were significantly high er in female than in male embryos in the last week of incubation. Howe ver, by 3 weeks after hatch, plasma corticosterone levels had decrease d significantly in both sexes and were not significantly different fro m one another. Plasma estradiol was significantly higher in female hat chlings than in male hatchlings. (C) 1998 Wiley-Liss, Inc.