Reduced egg shell permeability affects embryonic development and hatchling traits in Lycodon rufozonatum and Pelodiscus sinensis

Abstract

The response of embryos to unpredictable hypoxia is critical for successful embryonic development, yet there remain significant gaps in our understanding of such responses in reptiles with different types of egg shell. We experimentally generated external regional hypoxia by sealing either the upper half or bottom half of the surface area of eggs in 2 species of reptiles (snake [Lycodon rufozonatum] with parchment egg shell and Chinese softshelled turtle [Pelodiscus sinensis] with rigid egg shell), then monitored the growth pattern of the opaque white patch in turtle eggs (a membrane that attaches the embryo to the egg shell and plays an important role in gas exchange), the embryonic heart rate, the developmental rate and the hatchling traits in turtle and snake eggs in response to external regional hypoxia. The snake embryos from the hypoxia treatments facultatively increased their heart rate during incubation, and turtle embryos from the upper-half hypoxia treatment enhanced their growth of the opaque white patch. Furthermore, the incubation period and hatching success of embryos were not affected by the hypoxia treatment in these 2 species. External regional hypoxia significantly affected embryonic yolk utilization and offspring size in the snake and turtle. Compared to sham controls, embryos from the upper-half hypoxia treatment used less energy from yolk and, therefore, developed into smaller hatchlings, but embryos from the bottom-half hypoxia treatment did not.

Effects of Eggshell Thickness, Calcium Content, and Number of Pores in Erosion Craters on Hatching Rate of Chinese Alligator Eggs

“…Nevertheless, both smaller and larger numbers of pores have negative impacts on embryo survival. The presence of excessively small numbers of pores leads to impaired oxygen exchange and, thus, increases embryo mortality [ 10 ], whereas overly high numbers of pores result in excessive gas and water exchange (and, thus, excessive water loss) between the embryo and the external environment, with severe negative impacts due to dehydration [ 9 ].…”

“…Gas exchange is also key to successful embryo development. During the gas-exchange process, external hypoxic conditions significantly affect the embryo’s yolk utilization and the size of the offspring [ 10 ]. Oxygen diffuses from the air into the embryo and is necessary for aerobic metabolism, while water vapor and carbon dioxide diffuse from the embryo into the air [ 37 ].…”

“…Moreover, the hatching rate of thin-shelled eggs is 3% to 9% lower than that of thick-shelled eggs. Most researchers have reported that thick eggshells provide the following advantages: (1) the full use of nutrients by the embryo (in chicken eggs) [ 7 ], (2) a reduced likelihood of bacteria entering the egg [ 8 ], (3) a reduced likelihood of egg dehydration [ 9 ], and (4) better protection against mechanical damage [ 10 ].…”