Abstract
Oviparous reptile embryos receive a significant proportion of their calcium from the eggshell. For chickens, ≥ 80% of hatchling calcium originates from the shell while for oviparous snakes the shell accounts for 20–25% of hatchling calcium. The chick chorioallantois, which lies just beneath the eggshell, expresses carbonic anhydrase II (CAII) late in development. CAII is hypothesized to provide protons that are pumped out of the chorionic epithelium to acidify the inner surface of the shell, dissolving calcium carbonate and liberating calcium ions for transport to the embryo. Using immunoblotting, we determined the pattern of chorioallantoic CAII expression during the development of an oviparous (Pantherophis guttatus) and viviparous (Virginia striatula) snake to test the hypotheses that 1) oviparous snakes express a mechanism similar to chickens for dissolving shell calcium and 2) CAII is not expressed placental calcium transport in viviparous snakes. In P. guttatus, chorioallantois expression of CAII increases late in development coincident with shell calcium transport to the snake embryo, supporting hypothesis 1. In V. striatula, chorioallantoic expression of CAII also increases coincident with placental calcium transport late in development suggesting that CAII may be involved in additional chorioallantoic functions such as gas exchange and/or acid‐base balance. Supported by NSF grant IOB‐06515695.
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