Effects of Eggshell Removal on Embryonic Skeletal Development and Post-Hatching in the American Alligator (Alligator mississipiensis)

RM 210

Embryonic archosaurs (crocodilians and birds) are known to sequester calcium from their heavily mineralized eggshell and use it to mineralize their developing skeleton. In order to test the importance of eggshell calcium to embryonic growth, we studied growth of embryos and hatchlings of the American alligator with and without the calcareous eggshell. The outer eggshell layer was manually removed early in incubation, and embryos (n=6) were sampled at weekly intervals until hatching. The experimental and shamhandled control eggs were incubated at 30ºC and 100% relative humidity. Results show that experimental (“shellless”) embryos were significantly smaller in body mass and length than their clutch-sibling controls. Under identical rearing conditions, experimental hatchlings did not demonstrate catch-up growth despite ad infinitum diet and remained significantly smaller than control hatchlings. Observation of biting behavior revealed that experimental hatchlings had more compliant lower jaws and generated weaker bite forces. Our results suggest that yolk calcium reservoir is sufficient for healthy development, but eggshell calcium is required for normal embryonic growth. We posit that increased calcium absorption during development allows the embryo to hatch at larger size, which ultimately allows greater force development during predation.