Energetics of lizard embryos are not canalized by thermal acclimation

In some species of ectotherms, temperature has little or no effect on the amount of energy expended during embryonic development. This phenomenon can result from either of two mechanisms: (1) a shorter incubation period at higher temperatures, which offsets the expected increase in metabolic rate, or (2) a compensatory decrease in the rate at which embryos expend energy for maintenance. To distinguish the relative importance of these two mechanisms, we quantified the acute and chronic effects of temperature on embryonic metabolism in the eastern fence lizard (Sceloporus undulatus). First, we measured metabolic rates of individual embryos at 27°, 31°, and 34°C. Second, we examined the capacity for thermal acclimation by measuring the metabolic rates of embryos at 30°C, after a period of incubation at either 28° or 32°C. As with adult reptiles, the metabolic rates of embryos increased with an acute increase in temperature; the Q₁₀ of metabolic rate from 27° to 34°C was 2.1 (±0.2). No evidence of thermal acclimation was observed either early or late in development. In S. undulatus, a shorter incubation period at higher temperatures appears to play the primary role in canalizing the energy budget of an embryo, but a reduction in the cost of growth could play a secondary role.