The sea anemone Actinia equina tolerates allogeneic juveniles but alters their phenotype

Abstract

Actinia equina is a variably coloured sea anemone that broods juveniles within its body cavity. Male, female and non-sexual individuals can produce juveniles, even after periods of isolation, and it has been suggested that this species is capable of reproducing by asexual or parthenogenetic means. Further evidence in favour of this hypothesis has been derived from similarities in coloration and in enzyme banding, as shown by electrophoresis, between offspring and their parents^1–3. A. equina does, however, produce gametes that are morphologically similar to those of other sexually reproducing anemones, which suggests that sexual reproduction must also occur^1–4. Thus far the only direct evidence of sexual reproduction has been the occurrence of adults containing differently coloured juveniles within their body cavity; however, this is unusual and indeed in some areas adults only contain juveniles of the same colour as themselves^1,2,5,6. Carter and Throp¹ have suggested that adults can select against sexually produced juveniles that are phenotypically different from themselves; as a result juveniles generally match their parents in coloration. We show here by means of fostering experiments that adults will brood allogenic juveniles. Surprisingly, juveniles may change colour to match that of their foster parent.