Growth and energetics of embryos of the gecko, Phyllodactylus marmoratus, a species with hard-shelled eggs

We measured water contents, growth of embryos and metabolic rates in hard-s helled eggs of the Australian gecko, Phyllodactylus marmoratus, throughout incubation to make comparisons between (1) the proportional water content a t oviposition of eggs of P. marmoratus and flexible-shelled eggs of lizards ; and (2) the dry-mass specific energy consumption during development in P. marmoratus and lizards with flexible-shelled eggs. Egg contents (i.e. excl uding eggshell) contained nearly 80% water, higher than reported for any ot her squamate reptile. Eggs were laid at embryonic stages 26/27-29, which is slightly earlier than for most other lizards. Incubation lasted 79-84 days at 25 degrees C and net water loss averaged just under 3 mg. Metabolism re flected the size of embryos, with little growth and low rates of oxygen con sumption during the first third of incubation. Thereafter, growth and oxyge n consumption increased, with oxygen consumption slowing after day 70. This pattern is similar to that of other species of lizard. Water content of em bryos fell from above 90% early in incubation to around 70% at hatching. Th us, the embryonic metabolic scaling factor was different when based on embr yonic wet and dry mass. The dry-mass specific energetic cost of development in P. marmoratus was lower than other lizards, but this result was not rel ated to having a hard-shelled egg. The respiratory exchange ratio suggests that embryonic metabolism is based on mixed protein and lipid, a pattern si milar to that in flexible-shelled eggs of lizards, but different from birds .