The Adaptations of the Rough Winkle, Littorina rudis, to Desiccation and to Dislodgement by Wind and Waves

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Abstract
L. rudis individuals living on cliffs use crevices to avoid being dislodged by wind and waves, or dried out at low tide. The adaptations of a crevice population are compared with those of a nearby boulder shore population. Compared to the boulder shore animals, L. rudis living in crevices are smaller and mature at a smaller size, and they produce larger numbers of smaller progeny. Similar results previously were explained as adaptations to high mortality occurring when the winkles outgrow the crevices on which they depend for shelter, but large winkles are able to survive well among the crevices. As adaptations to avoid being dislodged, the winkles from the crevice population have a relatively large foot and are more reluctant than individuals from the boulder shore to withdraw into their shells when exposed to desiccation. The crevice animals live in a much drier environment than the boulder animals, but, despite this, are less resistant to desiccation. Because adaptations to avoid being dislodged conflict with adaptations to avoid desiccation, L. rudis from cliffs are likely to suffer high mortality throughout life, rather than the size-specific mortality assumed by previous workers. This can explain the observed life-history strategy.