Temperature constraints on phenotypic plasticity explain biogeographic patterns in predator trophic morphology

摘要

ABSTRACT: Phenotypic plasticity in feeding structures allows invasive predators to adjust to variation in prey defenses, but the abiotic milieu may constrain the extent or rate of the response. In the northwest Atlantic Ocean, the introduced European green crab Carcinus maenas encounters latitudinal differences in shell thickness of its snail prey, Littorina obtusata, and water temperature. To determine whether claw size in this heterochelous species responds to broad-scale differences in prey armor or water temperature, we reared C. maenas on a diet of thick- or thin-shelled L. obtusata at 16 or 10°C. At the higher temperature, crusher claw size increased significantly more at the molt relative to carapace width increase for crabs raised on the thick-shelled rather than thin-shelled diet. The lower temperature inhibited trophic responses in the crusher claw by reducing foraging performance on thick-shelled snails, and lower temperature also prolonged the molt interval. Cutter claw growth showed no diet effect at either temperature. Non-additive responses to multiple cues highlight the importance of testing for phenotypic plasticity over a range of environmental backgrounds and help explain post-invasion biogeographic patterns between an introduced predator and its prey.