Biochemical-genetic and ecological evidence that red/brown individuals of the anemone Actinia equina comprise two morphs in Britain

Abstract

A study of the sea anemone Actinia equina L. displaying red to brown column coloration was conducted on British shores in 1981 and 1982 in order to assess the ecological significance of discontinuous variation in pedal disc colour. Two ecologically distinct morphs have been revealed. One is characterised by having a red/pink pedal disc, and by being homozygous slow or heterozygous at a hexokinase locus, whilst the other has a grey/green disc and is homozygous fast. The former is relatively more common on the upper-mid shore and on vertical rock faces, whereas individuals of the latter occur more frequently at lower levels, and are relatively more abundant on horizontal surfaces. Correlated with this is a dichotomy in the strength of attachment of the disc to the substratum; anemones having red/pink discs adhere relatively more firmly. Evidence from brood size analysis suggest that the morphs are subject to differential selection; the commoner one at many site examined had a larger median brood size. At present, none of our data on gene-enzyme variation suggests that red to brown anemones in Britain comprise more than one species. Nevertheless, it is argued that local speciation is potentially likely to occur as a result of disruptive selection.