Calcium metabolism in olive ridley turtle eggs during embryonic development

Analyses of calcium, magnesium, sulphur, potassium and phosphorus content of the eggshell, yolk-albumen and embryos of olive ridley turtle, Lepidochelys olivacea, have been carried out at various stages of embryonic development. Calcium is the major inorganic constituent in the egg (shell and yolk-albumen) and embryos. Other elements are present either in trace or in minute trace amounts. The egg contents (yolk and albumen) provide only 40% of the embryonic calcium requirement of the hatchling. The remaining 60% is provided by the eggshell. The eggshell also undergoes a similar reduction in its calcium content from laying to hatching. Elements other than calcium present in the yolk-albumen are sufficient for normal embryonic development. The movement of calcium from the eggshell to the embryo starts at about the 40th day of development at 29.5 degrees C. Birds, turtles and crocodiles use their eggshell as the secondary source of embryonic calcium requirement. This dependence on the eggshell varies in different groups which is highest in birds and lowest in crocodiles.

Ultrastructure and characteristics of eggshells of the olive ridley turtle (Lepidochelys olivacea) from Gahirmatha, India

The structure of a chelonian eggshell is of prime importance for the developing embryo. It acts as a protective covering as well as mediator in the exchange of heat and water. The fresh eggshell of the olive ridley (Lepidochelys olivacea) turtle displays a variety of structural forms in their aragonite framework. Its netted substrate, loose texture and poorly organised crystallites favour the easy exchange of air and water during its development. The shell consists mostly of calcium in carbonate form and K, Mg, Fe, Ni, Pb, Zn, Co, Cr, Cu, Mn and Cd in traces. Ba and Sr in traces are also a feature of the thermal analysis graph. Phosphorous was not detected in the shell and its absence eliminates an earlier suggestion of it being a key factor in the development of aragonite crystals in the inorganic structure of marine turtle eggshells. Its combustion characteristics, which have not been previously reported, are recorded.