The lek paradox arises when choosy females deplete the genetic variance for male display traits from a population, yet substantial additive genetic variation (VA) in male traits persists. Thus, the lek paradox can be more generally stated as one of the most fundamental evolutionary questions: What maintains genetic variation in natural populations? One solution to this problem may be found in the condition-dependent nature of many sexually selected traits. Genotype × environment (G × E) interactions can maintain VA under conditions of environmental heterogeneity provided certain restrictions are met, although antagonistic pleiotropy has also been proposed as a mechanism. Here, we provide evidence for G × E interactions and against the role of antagonistic pleiotropy in the maintenance of VA for sexually selected traits. Using inbred lines of the lesser waxmoth Achroia grisella, we measured VA for song attractiveness, condition and development rate under different competitive environments and found that genotypes differed in their plasticity. We argue that variation persists in natural populations because G × E interactions prevent any one variant from producing the optimal phenotype across all environments.