Light is essential for embryonic development in many oviparous animals including fish,amphibians,and birds.However,light may be harmful for reptile embryos developing underground where they are in complete darkness and beneath thin eggshells.Nonetheless,how embryonic light conditions affect reptile development and offspring remains largely unknown.Here we incubated eggs in dark and light conditions to determine the effects of light exposure on embryonic development and offspring visual ability,spatial cognitive ability and growth in a lacertid lizard,Eremias argus.Our experiments demonstrated that light stimulation shortened incubation duration of eggs,but did not affect hatching success,offspring size,visual ability or survival.More interestingly,light exposure during incubation decreased spatial cognitive ability and post-hatching growth of offspring.On the basis of negative effects on offspring growth rates,our study indicates that in squamate reptiles with thin eggshells,light exposure in early development has negative effects on offspring cognitive ability.