Is water uptake by reptilian eggs regulated by physiological processes of embryos or a passive hydraulic response to developmental environments?

Moisture availability is critical for successful embryonic development in many organisms. In most oviparous reptiles, for example, water exchange between eggs and the surrounding environment can have substantial fitness consequences, but regulation of this process is unclear. Here, we evaluate whether water uptake by eggs of the lizard Anolis sagrei is regulated by the presence of a live embryo or is a passive hydraulic response to substrate moisture conditions. Many eggs laid in our captive colony were infertile or contained embryos that died during early stages of development, yet these ‘dead’ eggs continued to gain mass similar to that of ‘live’ eggs at least during the first half of incubation. Our results suggest that water uptake by eggs is largely a passive hydraulic process during the first half of incubation, but active regulation by embryos may be necessary during latter stages. Maternal effects (e.g., deposition of salts into yolk) could influence this passive process during early incubation.