AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 6 1541-R1547, Copyright © 1989 by American Physiological Society
Mobilization of calcium, phosphorus, and magnesium by embryonic alligators (Alligator mississippiensis)
M. J. Packard and G. C. Packard
Department of Biology, Colorado State University, Fort Collins 80523.
The yolk of an alligator (Alligator mississippiensis) egg contains
approximately 115 mg of Ca, 180 mg of P, and 17 mg of Mg at oviposition.
This compartment is the primary (or sole) source of P and Mg for the
forming embryo. Both of these elements are depleted rapidly from the yolk
once the embryo enters the growth phase of development. The yolk also is an
important source of Ca for the embryo, particularly during the first
two-thirds of incubation. During the last trimester of development,
however, the embryo supplements Ca from the yolk with Ca mobilized from the
eggshell. Indeed, more Ca is withdrawn from the eggshell during the last 2
wk of incubation than can be used by the embryo in skeletogenesis. The
excess Ca is stored in the yolk, thereby causing net transfer of Ca to
shift from withdrawal from the yolk to deposition in the yolk.
Consequently, the residual yolk in the hatchling alligator contains a
substantial reserve of Ca to support skeletal growth during the neonatal
period. The pattern of mobilization and deposition of Ca during
embryogenesis in alligators is similar to that characterizing avian
embryos, but is distinct from that characterizing embryos of all other
oviparous reptiles.
