We evaluate the extent to which males and females evolve along similar or different trajectories in response to the same environmental shift. Specifically, we use replicate experimental introductions in nature to consider how release from a key parasite (Gyrodactylus) generates similar or different defense evolution in male versus female guppies (Poecilia reticulata). After 8-12 generations of evolution, guppies were collected from the ancestral (parasite still present) and derived (parasite now absent) populations and bred for two generations in the laboratory to control for non-genetic effects. These F2 guppies were then individually infected with Gyrodactylus and infection dynamics were monitored on each fish. We found that parasite release in nature led to sex-specific evolutionary responses: males did not show much evolution of resistance, whereas females showed the evolution of increased resistance. Given that male guppies in the ancestral population had greater resistance to Gyrodactylus than did females, evolution in the derived populations led to reduction of sexual dimorphism in resistance. We argue that previous selection for high resistance in males constrained (relative to females) further evolution of the trait. We advocate more experiments considering sex-specific evolutionary responses to environmental change.