Invasion success can be enhanced both by evolution within the introduced range and by behavioral plasticity, but the importance of these processes for most invasions is not well understood. Previous research demonstrates that rusty crayfish (Orconectes rusticus) from invasive populations grow more rapidly than O. rusticus from native populations when raised in common conditions, suggesting that rapid growth has evolved since the introduction of O. rusticus. We hypothesized that O. rusticus from invasive populations achieve faster growth by allocating more time to foraging and less time to defense, which could result in increased vulnerability to predation. We conducted a behavioral experiment to test the effects of range (native or invaded) as well as plasticity (as induced by exposure to predators) on crayfish foraging and predator avoidance behavior. We collected O. rusticus eggs from native and invaded range populations and reared juveniles in common conditions either with predatory fish present or absent. We then quantified the amount of time that crayfish spent active (walking or feeding) in a laboratory experiment with and without predatory fish.
Results/Conclusions
In support of our hypothesis, O. rusticus from the invaded range were more active than O. rusticus from the native range (by 69%) when fish were absent. When fish were present, however, both native and invaded range crayfish were inactive. Further, crayfish from both ranges that were reared with fish had lower activity levels than those reared without fish (by 64%), especially when fish were present in the trial. Overall, our results suggest that the behavioral response of O. rusticus to predators is plastic, but O. rusticus activity level in the absence of predators has evolved since O. rusticus were introduced. Because previous work indicates that active crayfish consume more prey than inactive crayfish, this change in behavior may be responsible for rapid growth in invasive O. rusticus, a trait that contributes to the strong ecological impacts of this invasive crayfish.