An examination of the proportions of pedal disc colour and isozyme phenotypes, in samples of Actinia equina L. collected from around Britain, has shown that individuals which are heterozygous for a gene complex involved in morph determination occupy a habitat intermediate in position to those occupied by the two homozygotes. It is concluded that A. equina may best be considered as comprising three morphs, rather than two as had been distinguished previously.

As the abundance of anemones in samples displaying a particular pedal disc colour phenotype decreases, the proportion of these individuals which possess atypical combinations of colour and hexokinase-i phenotypes increases. This result is interpreted as indicating that individuals are subject to differential selection in different habitats, dependent upon their genotypes at hexokinase-i, or those at some other tightly linked locus.

Introduction

Our recent work on Actinia equina L. has revealed the existence of two morphs amongst anemones collected from British coasts, having column coloration ranging from red to brown (Quicke, Donoghue & Brace, 1983). One morph displays pedal disc colour (coloration) (PDC) ranging from red to pink (R), and occurs in the upper part of the intertidal range of this species, where it is commonly found firmly attached to vertical rock faces. The other has a grey (G) or green (H) pedal disc, which may sometimes display contrasting red or orange radial lines (L); these colour phenotypes will be collectively referred to as GHL. This latter morph occurs predominantly at a lower tidal level, where it usually occurs on horizontal surfaces to which it adheres relatively weakly.