Abstract
A fibrous and calcified shell characterizes eggs of oviparous amniotes and likely serves multiple roles during development. Calcium deposited on the outer shell surface is transported to the embryo late in development by the chorioallantoic membrane. Embryos of the egg‐laying corn snake Pantherophis guttatus acquire 28% of their calcium from the shell. To test the hypothesis that shell calcium is required for embryonic development, we reduced shell calcium by manually removing (peeling) the outer shell layer shortly after oviposition. Embryonic growth, calcium accumulation, bone ossification and chorioallantoic calcium transport protein expression were compared between treated and control groups. Hatchlings from peeled eggs were significantly shorter and lighter. Peeling delayed skull ossification (8 of 26 bones) early in development, although differences disappeared by hatching. However, hatchlings from peeled eggs showed significantly reduced ossification of caudal vertebrae. Calbindin‐D28K expression (marker for calcium transport activity) in the chorioallantois was reduced in peeled eggs. We conclude that reduced shell calcium retards growth of embryos and alters ossification patterns in corn snakes. Furthermore, the mechanism of calcium mobilization from the eggshell is responsive to variation in shell calcium content. (NSF grant IOB‐06515695. WTR supported by AOA fellowship.)
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