Placental Nutrition in the Viviparous Lizard Niveoscincus Metallicus: The Influence of Placental Type

The ion, energy, lipid, nitrogen and fat-soluble vitamin contents of freshly ovulated eggs and neonates of the viviparous lizard Niveoscincus metallicus were measured to quantify uptake of nutrients across the placenta. This species is particularly interesting because it has a chorio-allantoic placenta that is intermediate in complexity compared to viviparous species that have been the focus of other studies. Newly ovulated eggs have a wet mass of 79.6±4.6 mg and a dry mass of 41.8±2.8 mg, compared to the neonates that have a wet mass of 224.2±8.2 mg and dry mass of 37.9±1.2 mg. Thus, there is no significant net uptake of dry matter across the placenta. Neonates have significantly less lipid (6.2±0.4 mg) than eggs (12.7±0.5 mg) but no significant difference in nitrogen (4.1±0.3 mg) compared to eggs (4.5±0.2 mg). Energy densities reflect the protein and lipid composition and the relative dry masses of the eggs and neonates. There is significantly more energy (1029.1±80.0 J) in the egg than in the neonate (858.2±36.6 J). The increase in the ash content of the neonates (2.9±0.2 mg) compared to fresh eggs (2.1±0.3 mg) was not significant, even though there was an approximately threefold increase in the amount of sodium (0.11±0.01 mg in neonates, 0.34±0.01 mg in eggs) and potassium (0.12±0.017 in neonates, 0.40±0.01 mg in eggs) in neonates compared to eggs. There was no significant uptake of calcium and magnesium during development. The egg lipids consisted of triacylglycerol (66.7±2.3%), phospholipid (18.9±0.7%), cholesteryl ester (4.9±1.6%) and free cholesterol (5.6±1.5%). The egg phospholipid contained comparatively high proportions of arachidonic and eicosapentanoic acids but low levels of docosahexaenoic acid (DHA), whereas the phospholipid of the neonate was greatly enriched in DHA. In the egg, the predominant vitamin E was α-tocopherol (62.6±3.4 mg g-1), although there was some γ-tocotrienol (3.5±0.3 mg g-1), and vitamin A was present (1.5±0.2 mg g-1). The ratio of neonate dry mass to egg dry mass of N. metallicus (0.91) lies between that of species with type I (0.78) and type III (1.70) chorio-allantoic placentae, confirming our conclusion that the placenta of N. metallicus is functionally intermediate, as well as intermediate in complexity, between these other two types