Actinia

Abstract: It has been known for a long time that the commonest British sea anemone, Actinia equina L., incubates its young in the gastric cavity (Dalyell, 1848).

Abstract: The reproductive blology of the beadlet anemone Actlnia equlna L has been a toplc of considerable research interest In recent years Several theories have been put forward to explain the origin of young anemones found brooded In the enteron of female, male and apparently asexual ~ n d l v ~ d u a l s , but to date, conclus~ve vidence has not been produced to substantiate any of these hypotheses In thls paper, evldence 1s presented based on the results of an investigation of isozymes from adult A equlna and thelr broods which demonstrates that the young are asexually produced The sea anemone Actinia equina L. is extremely comnlon on rocky shores throughout Europe (e. g. Stephenson, 1935; Manuel, 1981) As a result of its abundance and ecological importance the species has been extensively studied (e. g Fischer-Piette, 1932, Crisp and Southward, 1958; Chia and Rostron, 1970; Schm~dt , 1971; Francis, 1973; Ottaway and Kirby, 1975; Edmunds et al . , 1976; Jones et al., 1977; Brace and Pavey, 1978; Rostron and Rostron, 1978; Brace et al . , 1979; Carter and Thorp, 1979; Gashout and Ormond, 1979; Carter and Thorpe, 1981) and remains a subject of considerable research interest. Because of its ecological importance, it is essential that the reproductive strategy of the species is fully understood but, to date, there ist still great controversy concerning its mode of reproduction (c.f. Chia and Rostron, 1970; Cain, 1974; Rostron and Rostron, 1978; Carter and Thorp, 1979; Gashout and Ormond, 1979; Carter and Funnel, 1981). It has long been known (Dalyell, 1848) that young anemones are brooded inside the enteron (gastric cavity) of an adult. More recent work (Chia and Rostron, 1970; Rostron and Rostron, 1978; Carter and Thorp, 1979; Gashout and Ormond, 1979) has shown that irrespective of sex, time of year or gonad condition, most adult Actinia equina will, under natural conditions, contain young anemones. It has been proposed by Chia and Rostron (1970) that O Inter-Research/Printed in F. R. Germany these young are derived from a sexually reproduced free swimming planula larva which metamorphosed to a young anemone only after seeking out and entering the eneteron of an adult. However, in a species which shows extensive colour polymorphism, it is difficult to reconcile this suggestion with the data of several authors (Cain, 1974; Carter and Thorp, 1979; Gashout and Ormond, 1979) showing that the brooded young are, at least generally, if not invariably, of the same colour as the parent. Cain (1974) proposed 4 possible mechanisms to explain these various observations. (1) Each colour variety (i.e. red, brown, green) may represent a different species. (2) Planula larvae may re-enter and be brooded by adults of their own colouration only. (3) A foster parent effect could control the colouration of the brooded offspring. (4 ) The juveniles may be produced asexually or by parthenogenesis within the adult in which they are found. In the light of subsequent work 3 of Caln's proposals can now be rejected. (1) Recent studies (Orr, 1980; Haylor, 1981; Haylor et al . , in preparation) have demonstrated that isoenzyme allele frequencies are randomly distributed between red and brown specimens, hence showing at least the red and brown colour morphs to be conspecific. (Green individuals, which were comparatively rare in the population, were not used in this study). (2) Pre and post metamorphic larval forms will not reenter the enteron of an adult (Carter and Funnel, 1980). (3) Larval colour is stable in the laboratory both outside and within the enteron of a contrasting-coloured foster parent (Carter, in preparation). Caln's fourth hypothesis, that asexual or parthenogenic reproduction could account for the brooded juveniles has not, to date been adequately tested. Mar. Ecol. Prog. Ser. 7: 227-229, 1982 Another suggestion (Carter and Thorp, 1979) is that sexual reproduction is followed by post-fertilisational selection for genotypes similar or identical to that of the brooding parent. However, observations (Gashout and Ormond, 1979) that individuals maintained in total isolation in filtered or artificial seawater will continue to produce broods of young over periods of time indicate the probability of asexual reproduction. Self fertilisation cannot account for the majority of these broods since many authors (Chia and Rostron, 1970; Carter and Thorp, 1979; Gashout and Ormond, 1979) have concluded that Actinia equina is very infrequently if ever hermaphrodite. Here we present data from isoenzyme studies which we consider demonstrate conclusively that the brooded young of Actinia equina are asexually produced. Specimens were obtained from a population at Fleshwick Bay, Isle of Man. Horizontal starch gel electrophoresis was used to screen these for 32 enzymes, of which 6 enzymes (7 loci) were found to b e usefully polymorphic. v v ------v ,,, --v m --------m -----m m -

Abstract: The role of the N-terminal segment 1-33 of equinatoxin II, a 20 kDa pore-forming protein from the sea anemone Actinia equina, was studied by N-truncation mutagenesis. A part of this segment was classified as being amphiphilic and membrane seeking. Wild-type equinatoxin II and its mutants lacking 5, 10 and 33 amino acid residues, respectively, were produced in Escherichia coli using T7 RNA polymerase-based expression vector. Soluble recombinant proteins were isolated from bacterial lysates and assayed for their inhibition by sphingomyelin, binding to red blood cells and hemolytic activity. The N-terminal deletion of 33 amino acids resulted in an insoluble protein, while mutants lacking 5 and 10 residues expressed increased relative avidity for sphingomyelin and red blood cell membranes. Their specific hemolytic activity was decreased, however, with increasing truncation. The results suggest that the N-terminus, which has been found to be conserved in sea anemone pore-forming toxins, contributes to the solubility of the equinatoxin II, but it is not essential for binding to lipid membranes. It is very likely that the N-terminus play a role in the formation of functional pores.

Abstract: THERE are many examples of aggression among anthozoan coelenterates: corals show interspecific interaction in which ranking may be obvious1, and inter-clonal aggression occurs in the anemone Anthopleura elegantissima2 Aggressive behaviour is also exhibited by some solitary anemones, such as Actinia equina L Both these species possess special structures bearing batteries of nematocysts, the acrorhagi which are used solely for offence3 We report here that there is a hierarchy of aggression, which is based on size, in A equina