Date of Award

1-23-2002

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Albert J.Fivizzani

Abstract

In oviparous vertebrates, maternal contributions to yolk material in the form of steroid hormones are thought to be responsible for several growth and behavior effects in the offspring. We initiated a series of experiments to determine the dynamics of yolk hormones in two species with temperature-dependent sex determination (TSD ), the snapping turtle, Chelydra serpentina, and painted turtle,Chrysemys picta, and one species with genetic sex determination (GSD), the Leghorn chicken,Gallus domesticus. The objectives o f these studies were to determine species and individual female differences in initial yolk steroid hormone levels and to monitor any changes in these levels during embryogenesis. Clutches of snapping and painted turtle, and chicken eggs were collected and individual yolks were analyzed to determine differences in initial hormone levels, between species and among females. For monitoring changes in hormone levels during development, snapping turtle eggs were incubated at a male-producing, female-producing or an intermediate temperature. Chicken eggs were incubated at 37.8°C. Eggs were sacrificed, embryos staged, the yolk material collected, homogenized and hormones extracted. Hormones [estradiol (Ej) and testosterone (T) for turtles; E2, T , androstenedione (A ), dihydrotestosterone (D H T ), for chickens] were separated via column chromatography and levels determined using RIAs. Initial hormone levels were in the nanogram per gram of yolk range for all three species. E . and T differed significantly between turtle species, with E^ levels greater than T in both. In contrast, T was greater than E, in the chicken. For all three species there were significant differences among clutches from different females in both E j and T . In the chicken, those differences existed in A and D H T , also. In the snapping turtle, significant decreases in both EL, and T occurred by the end of development that were significantly affected by incubation temperature. Eggs incubated at female-producing temperatures maintained high E^, those at male-producing temperatures had low EE^, and eggs incubated at pivotal temperatures had intermediate levels of EE^. Declines in T were similar at all temperatures, except just after the sex determining period, when T levels decreased more at the male-producing temperature only. In the chicken, significant decreases occurred in A, DITT and T during embryogenesis. A fter an initial decline, underwent a significant increase between embryonic stages 40 and 45, that may represent early embryonic production o f EL, by the developing gonads

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