Meeting Abstract
The mineralized eggshell of Reptilia was a major innovation in the evolution of the amniotic egg. Maternally deposited calcium serves to strengthen the eggshell and provide a source of nutrients for developing embryos. Embryos of oviparous reptiles extract calcium from eggshells but vary in their dependence on this source. In the corn snake, Pantherophis guttatus, embryos obtain most calcium from yolk, but also mobilize calcium from the eggshell. This suggests that acquisition of eggshell calcium may be facultative and that yolk provides sufficient calcium for successful development. We tested the hypothesis that embryonic development is not dependent on eggshell calcium by manipulating calcium availability. The outer calcareous layer of the eggshell was either left intact (control) or peeled off recently oviposited eggs. There was no difference in survivorship or length of incubation between treatments. We measured calcium content of hatchlings and analyzed skeletal development using cleared & stained specimens. Hatchlings from intact eggs contained more calcium and were larger in mass and length than siblings from peeled eggs. There were no observable differences in ossification but hatchlings from intact eggs had longer skulls and vertebrae. Our results indicate that mobilization of eggshell calcium is not a requirement for successful embryonic development of P. guttatus but does serve to augment yolk calcium. This pattern would favor embryos with a greater capacity to mobilize calcium from the eggshell by promoting growth and enhancing hatchling fitness.
