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Phenotypic plasticity typically is induced by environmental heterogeneity or stress, and is manifest by changes in behavior, morphology, or physiology. In amphibians, phenotypic variation is strongly influenced by the quality of the aquatic environment in which larvae develop. The stability of the aquatic environment and conspecific density are two important environmental stressors. We investigated whether larval populations of Rhine spinulosa subject to varying levels of hydroperiod and intraspecific competition exhibit phenotypic plasticity in their life-history characteristics. Egg clutches were collected from an arid region, within Parque Nacional Los Cardones. Larvae were exposed to different levels of hydroperiod and conspecific density in the laboratory. Development time and size at metamorphosis were recorded. Our results show that larvae from different clutches respond plastically in their life- history traits. Conspecific density was the most influential variable.