text: Key adaptations are adaptations that allow a group of organisms to diversify. Daphnia lumholtzi is a water flea that is able to form rigid head spines in response to chemicals released when fish are present. These phenotypically plastic traits serve as an induced defense against these predators. A study showed that Daphnia pulicaria is competitively superior to D. lumholtzi in the absence of predators. However, in the presence of fish predation the invasive species formed its defenses and became the dominant water flea in the region. This switch in dominance suggests that the induced defense against fish predation could represent a key adaptation for the invasion success of D. lumholtzi. A defensive trait that qualifies as a key adaptation is most likely an example of escape and radiate coevolution.