Biochemical-Genetic and Acrorhagial Characteristics of Pedal Disc Colour Phenotypes of Actinia Equina

Abstract

An examination has been made of pedal colour phenotypes exhibited by the three morphs of the anemone, Actinia equina L., which are distinguishable on the basis of allelic identity at two enzyme loci. The U (upper mid shore) and M (lower mid shore) morphs have pedal discs ranging in colour from red to pink, whereas the L (low shore) morph displays a grey to green pedal disc. Significant differences in the proportions of U and M morphs were found between samples of anemones having red and pink pedal discs, obtained from Burniston, N. Yorkshire, but these were not sufficiently clear cut to permit visual separation of the two morphs. Neither the pink nor red, pedal disc colour categories were comprised solely of anemones of one morph.A comparison of acrorhagial features (size, type, colour and number) between samples of anemones displaying various pedal disc colours, has shown that they are clearly divisible into three groups with respect to pedal coloration: (1) dark red; (2) light red and pink;(3) gr e y and green (with or without contrasting radial lines). In the absence of isozyme data relating to anemones possessing different acrorhagial features, it is not possible at present to state whether or not these characteristics will prove to be of assistance in visually distinguishing between the U and M morphs.It is cautioned that the differences discerned in characteristics could be related to, and modified by, the incidence of aggressive encounters within each of the pedal disc colour groups. I N T R O D U C T I O NPrevious work has shown that three ecologically disinct morphs can be identified amongst beadlet anemones, Actinia equina L., ranging in column coloration from red to brown (Quicke, Donoghue & Brace, 1983;Quicke & Brace, 1984;Quicke et al. 1985). Each is adapted to a different inter-tidal range, and is characterized by a multi-locus gene complex, which includes loci encoding a number of metabolically important enzymes, pedal disc coloration and probably strength of pedal attachment. They have been named the upper (U), mid (M) and lower (L) shore morphs, and are relatively most abundant on the upper mid, lower mid and low shores respectively. Members of the U morph are typically homozygous slow and fast at a hexokinase locus and a malate dehydrogenase locus respectively, whereas those of the L morph are typically homozygous for the other allele at each of these loci; M morph individuals are heterozygous at both.We have found that pedal disc coloration may be used to distinguish the majority of L morph individuals from members of the other two. L individuals

Divergence of Nematocysts in Two Colour Morphs of the Intertidal Beadlet AnemoneActinia Equina

“…Given the gradation of column colours in Actinia 'equina' from red, to brown, orange and green, finding a boundary characteristic of a species will always be highly problematic. Although pedal disc colour enables one reproductively isolated morph of Actinia to be identified, two apparently phenotypically indistinguishable reproductively isolated morphs remain, both of which possess red/pink pedal discs; Donoghue et al (1985) suggested that pink or dark red colour may be weakly associated with genotype, but this is far from diagnostic. Furthermore an analysis of acrorhagial characters also failed to find completely diagnostic characters to distinguish between species (Donoghue et al, 1985).…”

Littoral Distributions and Evidence For Differential Post-Settlement Selection of the Morphs of Actinia Equina

“…As yet we have no infallible method for separating the U and M morphs without resort to electrophoresis, though differences in (1) acrorhagial morphology, and (2) acrorhagial and pedal disc coloration, exist between all three morphs (Donoghue, Quicke & Brace, 1985). Differences in aggressive behaviour between the morphs have also been discerned.…”

Phenotypic Identification of three Genetically Differentiated Morphs of the Intertidal Beadlet Anemone Actinia Equina (Anthozoa: Cnidaria)

“…The L morph can be readily identified because it has a green or grey coloured pedal disc bordered by a blue line (Quicke et al, 1985). Pedal disc colour does not distinguish between the U and M morphs, however, because they both have red to pink coloured pedal discs (Donoghue et al, 1985).…”

“…They are conspicuous structures packed with holotrichous nematocysts and are used for aggressive behaviour. An analysis of various acrorhagial parameters in specimens of A. equina indicated some significant associations with pedal disc colour, although no character proved to be diagnostic with pedal disc colour (Donoghue et al, 1985). Attempts to distinguish morphs of A. equina have been hindered because although genetic differentiation can be shown in the laboratory other means by which the U and M morphs can be unambiguously identified have not been found.…”

“…The U and M morphs were distinguished using standard techniques of starch-gel (12-5% w/v) enzyme electrophoresis to examine the diagnostic bi-allelic genetic locus coding for malate dehydrogenase; the U morph is homozygous fast whilst the M morph is heterozygous (see Quicke et al, 1983;Quicke & Brace, 1984;Perrin, 1993;Lynch, 1996). Following Donoghue et al (1985) the acrorhagi of each morph were counted, measured, categorized as either simple or compound and their colour was recorded.…”