Cracks In Eggshells Impair Embryonic Growth In The American Alligator

Late-term embryos of archosaurs mobilize calcium from their mineralized eggshells in order to support musculoskeletal development. Previous studies on the American alligator showed that full removal of the eggshell leads to undersized embryos and hatchlings with weakly mineralized skeletons. How much of that effect is due to loss of eggshell structural integrity has not been investigated to date. We compared embryonic development and growth in eight clutches (192 eggs), collected over three seasons. Eggshells were either peeled, cracked, or shamhandled (control) at embryonic stages 16-18. All eggs were incubated for 35-40 days at 30°C in full humidity. Controlling for initial egg mass, we found that cracking the eggshell reduced embryo mass by 11%, and peeling the eggshell by 30%. Controlling for embryonic mass, whole-body proportions (total, snout-vent, femur, and head 20 lengths) were similar between treatment groups. Relative to femur length, however, wet mass of the caudofemoralis muscle (a major hind limb retractor) was 15 significantly reduced in embryos from cracked (-9%) and peeled (-23%) eggs. Eggshell fracture was unlikely to compromise calcium supply, given that eggshell crystals retained an intimate association with the underlying shell membrane. Overall, we show that eggshell fracture during rough handling/transport of eggs can have deleterious effects on embryonic growth and may impair hatchling escape performance from the nest. Our findings have implications for crocodilian conservation and egg ranching efforts, and may impact egg collection methods to minimize eggshell fracture. Further, researchers working on crocodilian eggs should consider controlling for structural integrity of eggshells in their studies