Maternal body volume constrains water uptake by lizard eggs in utero

1. Flexible shelled eggs of squamate reptiles normally take up substantial amounts of water, and swell accordingly, during development. However, most water uptake occurs after oviposition, beginning immediately or soon after oviposition, and water uptake is severely restricted in eggs that are retained in utero past the normal time of oviposition.

2. These observations suggest that some aspect of retention in the oviductal environment limits the amount of water eggs can absorb prior to oviposition.

3. This paper presents evidence, from two species of Sceloporus lizard, supporting the hypothesis that limited space within the mother’s body cavity physically constrains the ability of eggs to expand, and thereby their ability to absorb water. When adjusted for maternal body size, the water content of a female’s clutch of eggs is negatively correlated with the dry mass of her clutch (the space available in the body cavity is finite, and thus a greater dry mass content leaves less volume for water).

4. If such a constraint on water uptake is widespread, it can have important implications for our understanding of the evolution of viviparity, the costs of reproduction, and the determinants of reproductive output in squamate reptiles.