ASYMMETRICAL DEVELOPMENTAL PLASTICITY IN AN INTERTIDAL SNAIL

Field and laboratory experiments were used to investigate the variation and phenotypic plasticity in the adhesive abilities of the intertidal snail Nucella lapillus between high- and low-wave-energy environments. Whelks from an exposed coast produced a larger pedal surface area and were more resistant to dislodgement than were similar-sized individuals from a protected shore. Tenacity (g/cm²) was similar between individuals from exposed and protected shores, indicating that variation in resisting dislodgement was solely a function of pedal surface area. Whelks from exposed and protected shores did not differ in pedal surface area as they emerged from egg capsules or when reared in the laboratory under uniform conditions, suggesting that variation between populations does not represent genetic differentiation. Individuals from high-and low-wave-energy environments reared intertidally produced a larger pedal surface area than did those reared in the laboratory. The extent to which pedal surface area increased corresponded to the intensity of wave action. These findings suggest that pedal surface area is a highly plastic character modulated or induced by the water turbulence accompanying breaking waves. A reciprocal-transplant experiment confirmed this notion but revealed an asymmetry in the plasticity. Snails from the protected site transplanted to an exposed shore formed a much larger pedal surface area than did controls reared on the protected shore. In contrast, whelks from a wave-swept shore transplanted to a protected shore differed little from their controls reared on the exposed shore. The asymmetric response parallels a possible asymmetry in the risks of acclimating to a temporally unpredictable environmental cue, such as wave action.