The metabolism of lipid and inorganic ions during embryonic development of the turtle was studied using the species Chelydra serpentina (snapping turtle) and Pseudemys rubriventris (red-bellied turtle). Further, a preliminary study on the effects of acidic deposition on the embryonic development of turtles was performed. During development, numerous changes occurred in the lipid proportions and fatty acid compositions as lipids were transported from the yolk to the hatchling. Lipid utilization was characterized by a large decrease in triglycerides and phospholipids and a corresponding increase in free fatty acids during the period of rapid growth in the embryo. This indicated that lipids were hydrolyzed in the yolk prior to transport to the yolk sac membrane (YSM). This was in contrast to what occurs during the much-studied avian metabolism where lipids are hydrolyzed in the YSM. In addition, triglyceride-derived polyunsaturated fatty acids (PUFAs) were preferentially utilized compared to other fatty acids present in the yolk and became concentrated in the brain, eyes, and heart of the hatchling, often as free fatty acids or phospholipids. However, the amount of PUFAs present in each organ was <1% of the amount originally present in the yolk, indicating a more than adequate PUFA content. Once in the YSM, docosahexaenoic acid (DHA) and arachidonic acid (ARA) were selectively incorporated into triglycerides and phospholipids, respectively.
The mobilization of eggshell calcium and magnesium was followed using chemical and microscopic techniques. Calcium was preferentially mobilized from the bottom and sides of the eggshell, facilitating pipping and resulting in a brittle, flaky eggshell. The embryonic turtle utilized the eggshell as a source of magnesium as well as calcium. This is the first study to show eggshell magnesium usage in an embryonic turtle.
Finally, a pilot study was performed to determine the effects of an acidic environment on egg production, growth, and development in embryonic turtles. Several limitations in sample design and size prohibit definitive conclusions and applicability to all turtles. Turtle egg production was unaffected by an acidic environment as indicated by clutch size and egg mass. In addition, the presence of heavy metals was not detected in any of the eggs and there were no significant differences in hatchling mass and carapace length from acidic environments versus hatchlings from non-acidic environments.
This thesis greatly expands the previously limited knowledge of lipid, calcium, and magnesium metabolism during embryonic development of the turtle. Because metabolism was investigated throughout development, a clearer picture is presented of the utilization and transformations of lipids that occur compared to previous studies, which only compare the freshly laid egg to the hatchling. Several characteristics of turtle embryonic lipid metabolism were unique when compared to the most-studied oviparous creature, the chicken, and may be characteristic of all reptilian embryonic development.