The origins of novel behaviors are poorly understood, despite behavior's hypothesized roles in evolution. One model, "genetic accommodation," proposes that selection on ancestral phenotypic plasticity may precede the evolution of novel traits. A critical assumption of genetic accommodation is that ancestral lineages possess heritable genetic variation for trait plasticity that is revealed in novel environments, thereby providing the raw materials for subsequent refinement of the novel trait in derived lineages. Here, we use a combination of behavioral and RNA-seq approaches to test this assumption in the context of a novel tadpole behavior: predatory cannibalism. Cannibalism evolved in the spadefoot genus