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In order to understand thermal adaptation of Rana chensinensis,and to test the optimality models,we measured preferred temperatures,avoidance temperatures,and lethal thermal maxima of this species at earlier developmental stages using an artificial thermal gradient.The preferred temperature of the animals at tadpole stage was 14.05℃±2.38℃,at metamorphosis stage 20.2℃±2.46℃,at stage of young frog soon after metamorphosis 22.11℃±2.72℃.There were two higher peaks in the preferred thermal intervals of the subject animals at all these stages,which is consistent with the prediction of the optimality models to a great extent.There was significant differences between the preferred thermal intervals of animals at different earlier developmental stages (F=136.222,P<0.001,df=2,N=150).The critical maximum avoidance temperature of the animals was 30.98℃±1.43℃ at tadpole stage,32.16℃±0.99℃ at metamorphosis stage,and 36.75℃±1.61℃ at the stage of young frog soon after metamorphosis.There was significant differences between the critical maximum avoidance temperatures of the animals at different earlier developmental stages(F=119.585,P<0.001,df=2,N=90).The lethal thermal maximum of the animals was 35.66℃℃±1.08℃ at tadpole stage,36.17℃±1.5℃ at the stage of metamorphosis,and 38.77℃±1.52℃ at the stage of young frog soon after metamorphosis.There was significant differences between the lethal thermal maxima of the animals at different earlier developmental stages (F=36.106,P<0.001,df=2,N=60).It could be concluded that Rana chensinensis has different preferred temperature,the critical maximum avoidance temperatures and lethal thermal maxima at different earlier developmental stages.Any environmental factor,such as a diurnal pattern of temperature,that follows an approximately sinusoidal trajectory through time will exhibit a bi- or trimodal distribution.The optimality models modeled the bimodal environment as a mixture of two normal distributions sharing a common standard deviation and separated by an intermodal distance,and these models predicted that three fitness peaks would appear when the intermodal distance of the bimodally distributed temperature was 17℃.The main results of our study support the optimality models.