The influence of thermal and hydric environments on embryonic use of energy and nutrients, and hatchling traits, in the wall lizards ( Podarcis muralis)

Abstract

Among (different) clutch variation in egg composition, influence of thermal and hydric environments on incubating eggs, embryonic use of energy and nutrients, and hatchling traits were studied in the wall lizard Podarcis muralis from a lowland population of Northern Spain. When initial egg mass was kept constant, we found that some measured egg variables such as water, lipid-free organic material, ash, calcium and magnesium in egg contents, and ash and magnesium in eggshell, remained remarkably constant, whereas other variables differed considerably among clutches. All viable eggs increased in mass over the course of incubation due to absorption of water, and mass gain during incubation was dependent on initial egg mass, temperature and substrate water potential. Variations in the wet mass of hatchlings among treatments stemmed mainly from variations in water content. Hatching success, embryonic use of energy and nutrients, and sex, size and mass of hatchlings were unaffected over a wide range of substrate moisture. The incubation length decreased as temperature increased. However, the effect of substrate moisture on duration of incubation varied with temperature. The influence of incubation temperature on the snout-vent length of hatchlings, if present, was very weak. Incubation temperatures did not affect the sex ratio and carcass dry mass of hatchlings, but significantly affected the tail length of hatchlings, with individuals from the highest temperature having the shortest tails. The energy expenditure of embryogenesis during incubation remained remarkably constant among treatments, and energy reserves in the hatchling were largely dependent on allocation of energy materials in eggs. A high incidence of dead-in-shell embryos occurred in eggs that were laid in June and, thereafter, when ambient temperatures were high. Deformed hatchlings were distributed nearly equally among treatments.