[Morphological data from reciprocal transplant experiment] - DRAFT: Summary of Morphological Data on Littorina obtusata from the Reciprocal Transplant Experiment (Local adaptation and the evolution of plasticity under predator invasion and warming seas: consequences for individuals, populations and communities)

Such variation is expected to initially favor plasticity in prey defenses but fixed defenses as invaders become established. Coincident with the range expansion of the invasive green crab (Carcinus maenas) in the Gulf of Maine we document rapid changes in shell thickness – a key defense against shell crushing predators – of an intertidal snail (Littorina obtusata).

These data summarize the results of reciprocal transplant experiments between snail (Littorina obtusata) populations in the northern and southern Gulf of Maine that were conducted 20 years apart. The results revealed that temporal shifts in snail shell thickness were driven by the evolution of increased trait means and erosion of thickness plasticity. The virtual elimination of the trade-off in snail tissue mass that often accompanies thicker shells is consistent with the evolution of fixed defenses under increasingly certain predation risk and are therefore consistent with the predicted impacts of spatiotemporal changes in green crab abundance throughout the Gulf of Maine.