Effects of eggshell removal on embryonic skeletal development in the American alligator (Alligator mississippiensis)

• Main Author: Membreno, Nelson Armando
• Format: Others
• Published: CSUSB ScholarWorks 2017
• Subjects: Eggshell; Eggs; Archosaur; Alligator; Calcium; Biology
• Online Access: https://scholarworks.lib.csusb.edu/etd/529; https://scholarworks.lib.csusb.edu/cgi/viewcontent.cgi?article=1626&context=etd

The eggshell of reptiles is essential for not only protecting the embryo, but can also serve as source of calcium for embryonic skeletal development. Whereas embryonic lepidosaurs and chelonians rely on their yolk sac for calcium during development, embryonic archosaurs mobilise eggshell calcium supply to both the embryo and the yolk sac. By the time archosaurs hatch, their residual yolk sacs have a calcium content equal or greater than at time of oviposition, which is used to support post-hatching growth. To date, no study has looked into how removal of the calcareous eggshell affects embryonic development in archosaurs. I tested how the removal of the calcareous eggshell affects embryonic and hatchling growth and biomechanic function of the skeleton in embryos and hatchlings of the American alligator (Alligator mississippiensis). Experimental eggs had their eggshell manually peeled, while control eggs were sham handled but otherwise not altered. Sampling of eggs occurred on a weekly basis until the end of incubation. Embryos, yolk sacs, and eggshells were removed and analyzed for morphological, histological and biomechanical parameters. Results show that at the time of eggshell peeling yolk sac calcium reserves were sufficient for experimental embryos to develop, but animals hatched in diminutive state. Serial clearing and staining of embryos revealed that onset of bone mineralization was similar for both treatment groups. Growth trajectory of experimental hatchlings parallelled that of control animals, without compensatory growth. Experimental hatchlings were observed to have flexible lower jaws and produced a weaker bite force than control hatchlings. Cross-sections of the mandible and femoral mid-diaphysis had a significantly reduced cross-sectional area in experimental hatchlings. I conclude that loss of the calcareous eggshell during incubation leads to severe constraint on growth and biomechanics of the alligator skeleton.