Placental nutrition in the Tasmanian skink, Niveoscincus ocellatus

Niveoscincus ocellatus is an important species in historical analyses of th e evolution of viviparity because it is the species upon which the type II chorioallantoic placenta was based. Here we describe the net nutrient uptak e across the placenta of N. ocellatus for comparison with other species of skinks with complex placentae. N. ocellatus is highly placentotrophic, with neonates being 1.68-times larger in dry matter than the fresh eggs. There is an increase of nitrogen from 6.3 +/- 0.2 mg to 9.2 +/- 0.6 mg, and ash f rom 3.8 +/- 0.3 mg to 6.7 +/- 0.6 mg. The increase in ash is made up by a m ore than two-fold increase in the amounts of calcium, potassium and sodium. There is no significant difference in lipids in the neonates compared to f resh eggs, so considerable lipid must have crossed the placenta to provide energy for embryonic development. N. ocellatus is significantly more placen totrophic than Niveoscincus metallicus, which also has a complex chorioalla ntoic placenta. Discovery of substantial placentotrophy in this genus confi rms that two lineages of Australian lygosomine skinks (represented by the g enera Pseudemoia and Niveoscincus) have evolved this pattern of embryonic n utrition and supports the hypothesis that the evolution of reptilian placen totrophy involves specialisations in addition to structural modifications o f the chorioallantoic placenta.