Lamellose Axial Shell Sculpture Reduces Gastropod Vulnerability to Sea Star Predation.

Marine gastropods exhibit a stunning diversity of shell sculpture, but the functional significance of many sculpture types remains unknown. Unfortunately, experimental tests of the functional significance of differences between species are complicated by other morphological differences, such as shell microstructure, aperture shape, and shell thickness, that may confound interpretation. The most robust experimental tests are therefore performed using different shell forms within a species. We took advantage of the extensive intraspecific shell variation in the common intertidal gastropod Nucella lamellosa to test the adaptive significance of axial lamellae, a type of shell sculpture found in numerous marine gastropod subfamilies. We offered three forms of N. lamellosa (lamellose, artificially smooth, and naturally smooth) to the predatory sea star Pisaster ochraceus under controlled laboratory conditions. Pisaster ochraceus consumed significantly fewer lamellose snails than either artificially or naturally smooth snails. We suggest that shell lamellae deter sea star predation by impairing their ability to capture or manipulate snail prey or by increasing prey effective size. These results suggest a credible hypothesis for the adaptive significance of lamellar sculpture in marine gastropods and provide a valuable missing piece to the story about adaptive phenotypic plasticity in N. lamellosa shell form.