Uterine and eggshell structure and histochemistry in a lizard with prolonged uterine egg retention (Lacertilia, Scincidae, Saiphos)
Article first published online: 16 AUG 2010
Copyright © 2010 Wiley-Liss, Inc.
Journal of Morphology
Volume 271, Issue 11, pages 1342–1351, November 2010
How to Cite
Stewart, J. R., Mathieson, A. N., Ecay, T. W., Herbert, J. F., Parker, S. L. and Thompson, M. B. (2010), Uterine and eggshell structure and histochemistry in a lizard with prolonged uterine egg retention (Lacertilia, Scincidae, Saiphos). J. Morphol., 271: 1342–1351. doi: 10.1002/jmor.10877
- Issue published online: 11 OCT 2010
- Article first published online: 16 AUG 2010
- Manuscript Accepted: 6 JUN 2010
- Manuscript Revised: 3 JUN 2010
- Manuscript Received: 20 APR 2010
- National Science Foundation. Grant Number: IOB-0615695
- Australian Research Council Discovery Grant
- uterine egg retention;
The eggshell of lizards is a complex structure composed of organic and inorganic molecules secreted by the oviduct, which protects the embryo by providing a barrier to the external environment and also allows the exchange of respiratory gases and water for life support. Calcium deposited on the surface of the eggshell provides an important nutrient source for the embryo. Variation in physical conditions encountered by eggs results in a tradeoff among these functions and influences eggshell structure. Evolution of prolonged uterine egg retention results in a significant change in the incubation environment, notably reduction in efficiency of gas exchange, and selection should favor a concomitant reduction in eggshell thickness. This model is supported by studies that demonstrate an inverse correlation between eggshell thickness and length of uterine egg retention. One mechanism leading to thinning of the eggshell is reduction in size of uterine shell glands. Saiphos equalis is an Australian scincid lizard with an unusual pattern of geographic variation in reproductive mode. All populations retain eggs in the uterus beyond the embryonic stage at oviposition typical for lizards, and some are viviparous. We compared structure and histochemistry of the uterus and eggshell of two populations of S. equalis, prolonged egg retention, and viviparous to test the hypotheses: 1) eggshell thickness is inversely correlated with length of egg retention and 2) eggshell thickness is positively correlated with size of shell glands. We found support for the first hypothesis but also found that eggshells of both populations are surprisingly thick compared with other lizards. Our histochemical data support prior conclusions that uterine shell glands are the source of protein fiber matrix of the eggshell, but we did not find a correlation between size of shell glands and eggshell thickness. Eggshell thickness is likely determined by density of uterine shell glands in this species. J. Morphol., 2010. © 2010 Wiley-Liss, Inc.