Introduction

The embryonic development of many reptiles takes place within an egg oviposited outside the body of the female. Energy stored in the egg is transformed into tissue as the embryo grows from a few cells to a hatchling capable of independent existence. The transformation requires oxygen while producing carbon dioxide, water and heat. All are exchanged between the embryo and the environment across the eggshell. If development is to occur successfully, these exchanges must operate within appropriate limits which describe an environmental niche within which development is feasible. Even within these limits development may vary as a function of environmental gradients.

The reptile egg is typically exposed to an environment shaped by local edaphic, hydrologic, climatic and biotic variables. The female can influence the environment to which her eggs are exposed in several ways. This influence may occur through the timing of reproduction, through nest site selection, through nest construction, through variation in clutch size and in a few cases, through the exercise of parental care. The physical character of the incubation environment and of the eggs, as well as the physiological processes occurring inside the eggs, determine the microclimate in which embryonic development occurs (Fig. 12.1).

Our understanding of how reptilian embryonic development is adapted to the incubation environment is not extensive. There is little information available to describe how variation in soil characteristics, hydrology, topography or local climates influence the environment around eggs.