Elf, P.K.*; Fivizzani, A.J.: Changes in Sex Steroid Levels in the Yolks of the Leghorn Chicken, Gallus domesticus, During Embryonic Development
We have hypothesized that yolk hormones play a role in sexual differentiation in species with temperature-dependent sex determination (TSD), in which incubation temperature determines the sex of the offspring. To compare possible differences in yolk hormone patterns between TSD animals and those with genetic sex determination (GSD), a series of experiments have been initiated using the Leghorn chicken, Gallus domesticus. The chicken was chosen for this study because its sexual differentiation has been well characterized. The purpose of these investigations was to determine changes in the levels of androstenedione (A), dihydrotestosterone (DHT), estradiol (E) and testosterone (T) in the yolks of chicken eggs during embryonic development. Eggs were collected, labeled for clutch and egg number, and incubated at 37.8oC. Eggs were sacrificed at predetermined times during development, embryos staged and yolk material collected. Yolks were homogenizedand hormones extracted. A, DHT, E and T were separated via column chromatography and hormones measured using RIAs. Results show decreases in the levels of both A and T during embryogenesis, similar to those we reported in the alligator, with A levels being significantly greater initially than those of all other hormones. DHT levels mirrored those of T. Chicken E levels however, differed from those we measured in both the turtle and the alligator. E levels were less than T throughout most of development, and though they do decline slightly, E levels in yolks of chicken eggs show a significant increase between embryonic stages 40 and 45.