Early plastic responses in the shell morphology of Acanthina monodon (Mollusca, Gastropoda) under predation risk and water turbulence

Abstract

Marine gastropods show pronounced plasticity in shell morphology in response to local environmental risks such as predation and dislodgement by waves. Previous studies have focused on juvenile and adult snails; however, adaptive plasticity might be expected to begin during embryonic and early post-embryonic stages as a means of increasing survivorship when individuals first become vulnerable. We tested the above hypothesis by measuring shell morphology of encapsulated embryos and hatchlings of Acanthina monodon exposed to predator odor and water turbulence. Subjects were assigned to 1 of 4 treatments: (1) predator odor + high water turbulence, (2) no predator odor + high water turbulence, (3) predator odor + low water turbulence, (4) no predator odor + low water turbulence (control). After approximately 1 mo, morphological traits of the shell were measured using geometric morphometrics. Hatchlings, but not encapsulated offspring, produced larger shells in the predator treatments. Encapsulated offspring and hatchlings produced thicker shells in the predator treatments, irrespective of water turbulence, whereas thinner shells were produced when high water turbulence acted alone. Even before hatching, A. monodon can, thus, respond adaptively to potential mortality factors characterizing the local external environment. Anticipating risk in this way should enhance survivorship from the point of hatching through the vulnerable juvenile phase to adulthood.