Tolerance to thermal stress in lizard embryos

Species distribution across geographic regions is greatly controlled by environmental temperature, especially when the animals are ectothermic. The current models of climate changes predict the increase of the average global temperature and the frequency and intensity of periods with extreme temperatures. These changes may have pronounced effects on ectothermic species capacities, survival and distribution. In fact, growing evidence demonstrates that environmental temperature is a particularly important factor in determining developmental rates, morphological, behavioral and performance-related traits, and final size of organisms. In reptiles, temperatures experienced by developing embryos determine offspring's sex (temperature-dependent sex determination). The incubation temperature also affects the duration of the incubation and the hatchling size, locomotion, and growth. Females of egg-retaining squamates lay eggs only when thermal environments are optimal for developing embryos. In this study, we examined the effects of thermal stress (both cold and warm ones) on the development of the oviparous Italian wall lizard Podarcis sicula. The results showed a severe negative impact of constant thermal stress on the viability of P. sicula embryos, resulting in lethality, reduced survivorship and abnormal embryonic development. A preliminary analysis on gene expression demonstrated changes in the transcriptome of lizard embryos in response to cold shock. These findings demonstrate that P. sicula embryos tolerate a very narrow temperature ranges and that thermal stress during embryonic development may be a critical factor for offspring adverse effects. This apparent higher sensitivity of embryos also suggests that many lizard populations will be most affected by global climate change, with severe reductions in hatchling production.