Thermal stress and morphological adaptations in limpets

1. On thermally stressful rocky shores, small, slow-moving ectotherms such as limpets exhibit morphological characteristics such as high-spired and heavily ridged shells which may reduce the likelihood of reaching stressful or lethal body temperatures. 2. The effects of shell height and shell surface area on predicted limpet body temperatures were tested with a previously developed heat budget model. The model was parameterized with morphological data from three species (Lottia gigantea, Patella vulgata and Siphonaria gigas), which differ dramatically in their morphology and in the body temperatures they are likely to reach in the field. 3. Limpet models and standard cones with higher height : length ratios lost heat to convection more readily than models with lower spired shells. 4. Heavily ridged shells lost heat to convection more readily than smoother shells, but this effect was only pronounced at high wind velocities. 5. When the heat budget model parameters were applied to a real environmental data set, the model predicts that maximum body temperatures and cumulative thermal stress vary among species. These differences are related primarily to the height : length ratio of the shell, and to a lesser extent to the presence of ridges. 6. These results suggest that some intra- and interspecific variation in limpet morphology may be phenotypic or evolutionary responses to variation in environmental temperatures. Our findings are supported by observed patterns of limpet morphological variation across natural thermal gradients.