Warming temperatures caused by climate change are predicted to vary temporally and spatially. For mid‐ and high‐latitude reptiles, the seasonal variation in warming temperatures experienced by embryos and hatchlings may determine offspring fitness, yet this has remained largely unexplored. To evaluate the independent and interactive influence of seasonal variation in warming temperatures on embryonic and hatchling development, we incubated eggs and reared hatchlings of a cold‐climate oviparous ectothermic species, the Heilongjiang grass lizard (Takydromus amurensis), following a 2 × 2 factorial design (present climate versus warming climate for embryos × present climate versus warming climate for hatchlings). We then evaluated embryonic and hatchling development, including hatching success, incubation period, initial hatchling body size, hatchling metabolic rate, growth rate and survival in the mesocosms. We found that warming temperatures shortened the incubation period and produced hatchlings with higher survival rates than those incubated under the present climate conditions. Similarly, hatchlings reared under a warming climate had similar growth rates and resting metabolic rates, but higher survival rates than those reared under the present climate. Hatchlings that experienced both warming incubation and warming growth conditions had the highest survival rates. This study revealed that moderate warming temperatures (Representative Concentration Pathway, RCP 4.5, 1.1–2.6°C) experienced by embryos and hatchlings interact to benefit hatchling fitness in cold‐climate oviparous ectotherms. Our study also highlighted the importance of integrating seasonal variation in warming temperatures when evaluating the responses to climate warming in multiple developmental stages in oviparous ectotherms.

Climate change poses different threats to animals across latitudes. Tropical species have been proposed to be more vulnerable to climate change. However, the responses of animals from tropical mountains to thermal variation and climate change have been scarcely studied. Here, we investigated the thermal biology traits of a tropical lizard (Takydromus kuehnei) distributed at high elevations (>950 m) and evaluated the vulnerabilities of T. kuehnei by thermal biology traits, thermal safety margin, and thermoregulatory effectiveness. The average active body temperatures of T. kuehnei in the field were 26.28°C and 30.65°C in April and June, respectively. The selected body temperature was 33.23°C, and the optimal temperature for locomotion was 30.60°C. The critical thermal minimum and critical thermal maximum temperatures were 4.79°C and 43.37°C, respectively. Accordingly, the thermal safety margin (1.23°C) and thermoregulatory effectiveness (1.23°C) predicted that T. kuehnei distributed in tropical mountains were not significantly depressed by environmental temperatures. This study implies that high-elevation species in tropical regions may not be severely threatened by ongoing climate change and highlights the importance of thermal biology traits in evaluating the vulnerability of species to climate change.