Contrast Between Solitary and Clonal Lifestyles in the Sea AnemoneAnthopleura elegantissima

Abstract

The common intertidal sea anemone Anthopleura elegantissima (Brandt) occurs in two forms the clonal aggregating form and the solitary form The obvious differences between the two apparently result from the presence of asexual reproduction in the clonal aggregating form and its absence in the solitary form resulting differences in growth form suit the two anemones to different lifestyles The clonal form is well suited to life higher in the mid intertidal Asexual reproduction resulting in moderately small individual size and close association with clonemates improves its resistance to physical stress (drag and desiccation) and makes it a superior competitor in exposed habitats higher in the intertidal where species diversity and predator pressure are low The larger solitary animals live in more protected microhabitats lower in the intertidal and subtidal and are probably more resistant to predation and less able to withstand physical stress or intense intraspecific competition The two forms also have different biogeographic ranges While the clonal aggregations are quite common at rocky sites at least as far north as Vancouver Island in British Columbia populations of solitaries have not been found north of Point Reyes California Apparently the two forms are re productively isolated phenotype frequencies are very different for clonals and solitaries living at the same locations while the between-sample variation within each form is relatively small These differences in phenotype frequencies biogeographic range and microhabitat suggest that the clonal anemones and the solitary anemones known as Anthopleura elegantissima are actually a sibling species pair.