Eggshell formation during prolonged gravidity of the tuatara Sphenodon punctatus

Journal of Morphology
A CreeKaren Reader

Abstract

Scanning electron microscopy (SEM) was used to examine the process of shell formation in tuatara. Tuatara carry eggs in the oviducts for ∼ 7-8 mo before nesting, a period of gravidity more than three times as long as in any other oviparous reptile. Our aim was to determine whether shell formation occurred rapidly after ovulation, or whether it occurred gradually throughout gravidity. Eggs were obtained from females in early gravidity (May, ∼ 1 mo after ovulation), midgravidity (August and September, 4-5 mo after ovulation), and late gravidity, immediately prior to nesting (December, 8 mo after ovulation). The shell membrane (fibrous layer) was well formed by May, but calcification of the outer surface had only just begun. Vertical columns of calcium carbonate were embedded in the shell membrane and appeared to erupt through the outer surface between early and midgravidity. Changes in the appearance of the outer calcareous layer were evident as gravidity progressed. In all shells, calcium carbonate was present as calcite. The appearance of the inner boundary (innermost layer of eggshell) was variable; some shells had a smooth and amorphous inner boundary as previously reported for tuatara and other reptiles, whereas other shells...Continue Reading

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Citations

Jul 13, 2002·The Journal of Experimental Zoology·Jane E Girling
Nov 16, 2011·Genesis : the Journal of Genetics and Development·Wendy L Johnston, James W Dennis
Apr 1, 1997·Journal of Morphology·Louis J Guillette, Alison Cree
May 16, 2021·Journal of Morphology·J Matthias StarckDaniel G Blackburn

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