Meeting Abstract

70.6  Monday, Jan. 6 09:15  Mobilization of Eggshell Calcium Promotes Embryonic Growth in an Oviparous Snake STEWART, J.R.*; ECAY, T.W.; East Tennessee State University, Johnson City stewarjr@etsu.edu

The mineralized eggshell of Reptilia was a major innovation in evolution of the amniotic egg. Inorganic components strengthen the eggshell and their proximity to embryonic tissues provides a potential source of nutrients to developing embryos. Evolution of a mechanism in the embryonic chorioallantoic membrane to mobilize eggshell calcium released the embryo from total dependence on yolk for calcium nutrition and increased the potential for further innovation in embryonic calcium acquisition. Embryos of many squamate reptiles are heavily dependent on yolk for calcium nutrition, yet mobilize some calcium from the eggshell. This nutritional pattern suggests that acquisition of eggshell calcium is facultative; i.e., yolk provides sufficient calcium for successful embryonic development, yet supplemental calcium from eggshell enhances embryonic nutrition. Embryos of the oviparous corn snake, Pantherophis guttatus, are highly dependent on calcium from yolk. We tested the hypothesis that embryonic development is dependent on eggshell calcium by manipulating eggshell calcium content. We peeled the outer layer of the eggshell of 12 clutches of recently oviposited eggs; control eggs were left intact. We sampled peeled and intact eggs periodically throughout incubation and measured calcium content of egg compartments. There was no difference in survivorship between treatments. Hatchlings from intact eggs contained 25% more calcium than siblings from peeled eggs. The increased calcium availability significantly impacted hatchling size. Hatchlings from intact eggs had 10% greater length and mass than siblings from peeled eggs. Our results indicate that mobilization of eggshell calcium is facultative and the ability of embryos to augment yolk calcium enhances hatchling fitness.