Placental nutrition in a viviparous lizard (Pseudemoia pagenstecheri) with a complex placenta

Abstract

The composition of egg yolks and neonates of the viviparous lizard, Pseudemoia pagenstecheri, one of the most placentotrophic reptiles studied to date, are described. Neonates (43.3 ± 5.2 mg) have twice the dry mass of the initial eggs (22.0 ± 1.9 mg). The protein content of neonates (29.1 ± 1.1 mg) is more than twice that of eggs (12.2 ± 1.1 mg), while the energy content (908.1 ± 107.4 J) is 1.6 times higher than that of the egg (565.0 ± 42.9 J). The energy densities of eggs (27.5 kJ g⁻¹) and neonates (23.1 ± 0.3 kJ g⁻¹) are similar to the energy densities of eggs and neonates of oviparous species. The total ash per neonate (4.1 ± 0.4 mg) is three times greater than that of the egg contents (1.4 ± 0.2). Neonates contain significantly more calcium, sodium and potassium, but not magnesium, than do eggs. Thus, the placenta has a quantitatively important role in supplying nutrients for the embryo. The proportions of triacylglycerol (66%), phospholipid (19%), and free cholesterol (5%) in the eggs are similar to those in eggs of birds and crocodilians, but the proportion of cholesteryl esters (7%) is much higher in eggs of P. pagenstecheri. The proportion of docosahexaenoic acid in the egg phospholipid is relatively low (1.4%) but rises to 5.4% in the neonate. The eggs contain vitamin E (mainly in the form of α-tocopherol) and vitamin A, but no detectable carotenoids. The overall composition of the eggs is not substantially different from that of oviparous species, suggesting that the small egg size relative to neonate size is a result of a reduction in egg size rather than modification by omission of some nutrients from the yolk. The pattern of placental nutrient provision of P. pagenstecheri contains both an obligate and a facultative component suggesting that enhancement of offspring quality through facultative placentotrophy is a general characteristic of placental reptiles independent of pattern of embryonic nutrient provision.