Embryos of the agamid lizard Amphibolurus barbatus are at developmental stage 29 of Dufaure and Hubert at the time of oviposition. Mobilization of calcium and other nutrients from the yolk proceeds slowly for the first half of incubation, during which time embryonic growth also proceeds slowly. During the second half of incubation, however, embryos withdraw calcium and other nutrients from the yolk very rapidly, and growth rates are correspondingly high. Approximately 60% of the calcium used by developing embryos is obtained from the yolk, but fully 40% of their requirement is met by calcium mobilized from the eggshell. Very little calcium remains in residual yolk of hatchlings, so this yolk must be used in maintenance metabolism rather than in growth of neonates. No dichotomy exists among oviparous, amniotic vertebrates with respect to sources of calcium used by developing embryos, but one does exist with respect to patterns of mobilization of this element. Whereas calcium is extracted from yolk of embryonic reptiles throughout incubation, it actually is deposited in yolk of embryonic birds after the midpoint in development.

Item Type:	Refereed Article
Keywords:	calcium, embryo, yolk, nutrient, growth, lizard, agamid, Amphibolurus barbatus
Research Division:	Biological Sciences
Research Group:	Zoology
Research Field:	Animal developmental and reproductive biology
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the biological sciences
UTAS Author:	Jones, ME (Professor Menna Jones)
ID Code:	130835
Year Published:	2018
Web of Science® Times Cited:	62
Deposited By:	Zoology
Deposited On:	2019-02-15
Last Modified:	2019-02-15
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