Meeting Abstract

137.4  Monday, Jan. 7  Importance of the calcareous eggshell to normal skeletal development in the American alligator MEMBRENO, N.A.*; ELSEY, R.M.; OWERKOWICZ, T.; California State University, San Bernardino; Rockefeller Wildlife Refuge, Louisiana Dept of Wildlife and Fisheries, Grand Chenier; California State University, San Bernardino membrenn@coyote.csusb.edu

During development, oviparous reptiles rely on both yolk and eggshell calcium stores for skeletal growth of the embryo. By hatching time, squamates and chelonians deplete the yolk almost completely of calcium. In contrast, embryonic archosaurs (crocodilians and birds) sequester calcium from the heavily mineralized eggshell and store it in yolk, so that the yolk sac can serve as a mobile calcium source in hatchlings. We studied the relative importance of eggshell calcium to normal development and growth of the American alligator (Alligator mississippiensis). At approximately three weeks after egg laying, the calcareous eggshell layer of the experimental eggs was completely peeled by hand, while clutch-matched control eggs were sham-handled but not altered. All eggs were incubated at 30°C and 100% humidity, and embryos were sampled at regular intervals until hatching. At first, there was no discernible difference in embryo growth. As incubation progressed, however, experimental embryos grew more slowly than sham embryos. At hatching, experimental embryos were 36% smaller than their sham siblings, whereas their yolk sacs were 3-4x larger. Despite being diminutive, experimental hatchlings were active and apparently healthy. Our results suggest that eggshell calcium is important for embryonic growth in alligator, but sufficient calcium reserves are found in the yolk. Shell-less embryos are capable of survival until and after hatching. We posit that evolution of heavily mineralized eggshells of archosaurs may have been driven by factors other than the need for calcium mobilization during embryonic skeletal development.