Interrelations Among Water and Energy Relations of Reptilian Eggs, Embryos, and Hatchlings

Reptilian eggs previously categorized with respect to the flexibility of eggshells appear to fall into two groups: endohydric eggs are those that are invested, by the female parent at the time of oviposition, with all of the water necessary to complete embryogenesis; and ectohydric eggs which need to absorb water from the nest medium tocomplete embryogenesis. Eggs of the Galapagos land iguana are unusual among most lepidosaurians by having very permeable parchment shells, but containing a large albumen (apparently serving as a reservoir of water for the embryo). It appears that the eggs of Galapagos land iguanas can exploit an endohydric habit without the rigid, impermeable shell seen in other endohydric eggs. This ability appears to be mediated by two factors: eggs of Galapagos land iguanas are laid in dry soils which are essentially impermeable to water, and the very large eggs of land iguanas have a relatively small surface area tovolume ratio which results in a relatively small exchange of water across the eggshell. It appears too that the water relations of Galapagos land iguana eggs will affect the energetics of both the contained embryo and the subsequent hatchling. Without adequate water, land iguana eggs will produce hatchlings that are both smaller and possess less fat to sustain thejuvenile during the first year of life.