Eggshell Calcium Influences Embryonic Growth in Pantherophis guttatus

The eggshells of oviparous reptiles provide structural stability during development and are a significant source of embryonic calcium. Hatchling corn snakes ( Pantherophis guttatus ) obtain approximately 25% of their calcium from the eggshell, primarily in late development. Removing eggshell calcium by peeling away the outer shell layers at early stages results in significantly shorter and lighter hatchlings. To test whether embryos can access environmental calcium to compensate for shell calcium lost to peeling, we incubated peeled and intact eggs in media with increasing calcium and monitored egg uptake of calcium with a calcium electrode. Intact eggs lose calcium in low calcium media (≤ 5 mM calcium) until about 10 days before hatching when they accumulate calcium. The timing of this calcium accumulation is consistent with expression of calcium transport pathways in tissues lining the inner shell. In contrast, peeled eggs in low calcium slowly accumulate calcium early and accelerate uptake at late stages in parallel with intact eggs. In high calcium media (20 mM) peeled and intact eggs exhibit a parallel pattern of increased calcium uptake at all stages. We conclude that corn snake eggs can access environmental calcium and that eggshell peeling and calcium supplementation is an experimental model to study the role of shell calcium in embryonic development and metabolism. (NSF Grant IOB‐06515695)