USF St. Petersburg campus Faculty Publications
Hatching and residual yolk internalization in lizards: evolution, function and fate of the amnion
Document Type
Article
Publication Date
2013
ISSN
1520-541X
Abstract
Most egg-laying vertebrates hatch without depleting the entire yolk reserve. The residual yolk is internalized before emergence from the egg is completed and the yolk is subsequently metabolized during early neonatal life. Here we provide the first description of the mechanism of yolk internalization in non-avian reptiles. We describe the hatching of two lizard species (Physignathus lesueurii and Varanus rosenbergii) and provide a step-by-step account of sequence of events leading to yolk internalization and emergence from the egg. We also conducted incubation experiments to determine the cause of failed yolk internalization. Contraction of the ruptured amnion is the mechanism by which the residual yolk is internalized, which provides an explanation for the functional significance of amniotic contractions. Failures of internalization occur when the amount of residual yolk exceeds that which can be enclosed by the ruptured amnion. We conclude that, because of the connections formed between the amnion and both the allantois and chorion, the pipping and retraction of the amnion pulls the chorioallantoic membrane (CAM) off the surface of the eggshell, which impairs the capacity for gas exchange and forces the embryo to breach the eggshell to commence breathing. We further speculate that the loss of amniotic contractions in mammals may indicate an incompatibility of amnion-assisted yolk internalization with viviparity, an evolutionary process that could be tested by examining viviparous squamates.
Language
en_US
Publisher
WILEY
Recommended Citation
Pezaro, N. , Doody, J. , Green, B. and Thompson, M. (2013), Hatching and residual yolk internalization in lizards: evolution, function and fate of the amnion. Evolution & Development, 15: 87-95. doi:10.1111/ede.12019
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
Comments
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