Inter-genotype aggression in the solitary sea anemone Actinia tenebrosa

Abstract

Acrorhagial fighting occurs between some pairs of adult Actinia tenebrosa, and such fighting almost always results in the locomotory withdrawal of the loser. Adults are also able to attack and kill juvenile conspecifics in laboratory conditions. In laboratory trials, 58 of 89 pairs of adults responded aggressively when placed in contact. Conflicts developed disproportionately often when adults were genotypically different, as judged by electrophoretic examination of 5 polymorphic enzymes, or when adults were markedly different in weight. Neither the sexual maturity nor presence of brooded juveniles affected the probability that conflicts would develop between adults. Weight did not affect the outcome of the conflicts. Presentation of apparently asexually produced juveniles to adults revealed that both the recognition and effector phases of the acrorhagial response are triggered by genotypic dissimilarity and not by size dissimilarity per se. Acrorhagial responses were initiated only on contact with juveniles from other adults. Localised release of asexually-produced brooded juveniles contributes substantially to recruitment within established populations of A. tenebrosa. Aggressive interactions between genotypes thus seem likely to play an important role in intra-specific competition for recruitment space.