Utilisation of lipids, protein, ions and energy during embryonic development of Australian oviparous skinks in the genus Lampropholis

The contents of eggs and neonates of the Australian skinks, Lampropholis gu ichenoti and L. delicata, are described and compared to allow interpretatio n of nutrient utilisation by the developing embryo. Even though the females are the same size, L. guichenoti lay smaller clutches of larger eggs (egg contents = 41.6 +/- 1.2 mg dry mass) than L. delicata (26.6 +/- 2.8 mg). Th e energy density is the same for eggs (30.5 +/- 0.9 J/g ash-free dry mass f or L. guichenoti and 29.9 +/- 1.1 J/mg for L. delicata) and neonates (22.5 +/- 1.3 J/mg for L. guichenoti and 23.5 +/- 0.4 J/mg for L. delicata) betwe en species. The amount of nitrogen (protein) in neonates is only slightly l ower than that in eggs, whereas there is a large and significant decline in total lipids. Thus, like some other skinks, protein is a source of metabol ic energy during embryogenesis, although not as important as lipid. Triacyl glycerol is the major lipid component of the eggs (80% of total lipid), wit h phospholipid forming only approximately 10% of the total lipid. The fatty acid profile of the phospholipid is distinguished by a high proportion of arachidonic acid (8%), a significant proportion of eicosapentaenoic acid (2 -4%) and a relatively low proportion of docosahexaenoic acid (2-3%) compare d to chickens. Eggs of both species have remarkably low concentrations of f ree cholesterol compared to other amniote eggs (0.7% for L. guichenoti and 1.3% for L. delicata). The loss of lipid during embryonic development is al most entirely due to the selective utilisation of yolk triacylglycerol, pre sumably for energy. By contrast, the amount of phospholipid recovered from the neonates was the same as that originally in the eggs. Moreover, signifi cantly more total cholesterol was present in the neonates than in the eggs, suggesting that biosynthesis of additional cholesterol occurred during dev elopment. The phospholipids of the neonates contain higher proportions of a rachidonic (11-12%) and docosahexaenoic (8%) acids than the phospholipids o f the eggs. Eicosapentaenoic acid is less prevalent in phospholipids in neo nates than in eggs. Neonates of both species contain significantly more cal cium than the fresh egg contents (L. guichenoti, eggs 0.303 +/- 0.051 mg), neonates 0.641 +/- 0.047 mg; (L. delicata, eggs 0.187 +/- 0.013 mg, neonate s 0.435 +/- 0.033 mg), presumably as a result of resorption of calcium from the eggshell. Interestingly, there is also significantly more sodium in ne onates than in the contents of fresh eggs (L. guichenoti, eggs 0.094 +/- 0. 010 mg, neonates 0.184 +/- 0.011 mg; L. delicata, eggs 0.084 +/- 0.011 mg, neonates 0.151 +/- 0.010 mg). There is no significant difference in the con tent of potassium and magnesium in eggs and neonates of either species. Alt hough the fresh eggs of L. delicata have a significantly higher sodium conc entration than L. guichenoti, there is no difference in the concentrations of calcium, magnesium, potassium or sodium in the neonates of the two speci es. (C) 2001 Elsevier Science Inc. All rights reserved.