Coexistence Shapes Antipredator Defenses

8 Invasive alien predators can impose strong selection on native prey populations and induce rapid 9 evolutionary change in the invaded communities. However, studies on evolutionary responses to 10 invasive predators are often complicated by the lack of replicate populations differing in 11 coexistence time with the predator, which would allow determining how prey traits change during 12 the invasion. The red swamp crayfish Procambarus clarkii has invaded many freshwater areas 13 worldwide, with negative impacts for native fauna. Here, we examined how coexistence time 14 shapes antipredator responses of the Iberian waterfrog (Pelophylax perezi) to the invasive crayfish 15 by raising tadpoles from five populations differing in historical exposure to P. clarkii (30 years, 20 16 years or no coexistence). Tadpoles from non-invaded populations responded to the presence of P. 17 clarkii with behavioral plasticity (reduced activity), whereas long-term invaded populations 18 showed canalized antipredator behavior (constant low activity level). Tadpoles from one of the 19 long-term invaded populations responded to the crayfish with inducible morphological defenses 20 (deeper tails), reflecting the use of both constitutive and inducible antipredator defenses against the 21 exotic predator by this population. Our results suggest that, while naive P. perezi populations 22 responded behaviorally to P. clarkii, the strong predation pressure imposed by the crayfish has 23 induced the evolution of qualitatively different antipredator defenses in populations with longer 24 coexistence time. These responses suggest that strong selection by invasive predators may drive 25 rapid evolutionary change in invaded communities. Examining responses of prey species to 26 biological invasions using multiple populations will help us better forecast the impact of invasive 27 predators in natural communities.