Meeting Abstract
P2.97 Friday, Jan. 4 Embryonic growth and calcium mobilization in oviparous and placentotrophic Australian scincid lizards GARLAND, C. P.; FREGOSO, S. P.; PRICE, E. K.; STEWART, J. R.*; ECAY, T. W.; HERBERT, J. F.; THOMPSON, M. B.; East Tennessee State University; East Tennessee State University; East Tennessee State University; East Tennessee State University; East Tennessee State University; University of Sydney; University of Sydney stewarjr@etsu.edu
Embryos of oviparous lizards have two sources of calcium for embryonic development: 1) calcium that accumulates in yolk during vitellogenesis, and 2) calcium carbonate deposited in the eggshell from oviductal secretions. Oviparous scincid lizard embryos rely heavily on both of these sources with the eggshell providing 30 � 50 % of hatchling calcium content. Eggs of viviparous lizards lack a calcified eggshell and calcium secreted by the uterus is delivered to the embryo across a placenta. We compared the pattern of calcium mobilization to embryos of the viviparous, placentotrophic scincid lizard, Pseudemoia pagenstecheri to that of a closely related oviparous species, Saproscincus mustelinus to test the hypothesis that the timing of embryonic uptake of calcium in placentotrophic species differs from oviparous species. Oviposited eggs of S. mustelinus contain twice the dry mass and ten times the calcium (yolk + eggshell) of recently ovulated eggs of P. pagenstecheri and embryos of both species receive a substantial amount of calcium from either the eggshell or placenta (54% and 85% respectively). The size of embryos of the two species does not differ until the latest embryonic stages when embryonic growth increases dramatically in both species and there is a high level of calcium mobilization from eggshell and placenta. By the final embryonic stage, embryos of P. pagenstecheri are larger and neonates contain 35% more calcium than hatchling S. mustelinus. We conclude that the peak calcium transporting activity occurs during the same developmental stages of both species but that the rate of placental transfer is greater than recovery from eggshell.
