Morphological Variability and Intraspecific Aggression in the Clonal Anemone, Anthopleura elegantissima

Abstract

Individuals of the aggregating anemone, Anthopleura elegantissima, occupy the rocky intertidal and form large clusters of polyps by splitting (fission). These organisms are known to attack neighboring, unrelated clone-groups and although genetically identical, fighting ability varies within a clone-group; individuals on the edge of the aggregation take the role of warriors, leaving those further inside the clone-group free to reproduce. This study examined morphological differences between successful and unsuccessful combatants, both within a colony and across different clone-groups. This may confer a competitive advantage to individuals within a colony or to the clone-group as a whole. Anemones were collected from three distinctly separate clonal colonies in a single bay and agonistic interclonal interactions were staged. Competitors were chosen at random within each functional class, with 15 reproducer and 15 warrior trials. Outcomes of the competitions were determined and variations in tentacle length, tentacle density and acrorhagi density were assessed between the winners and losers, as well as within clone-groups. Warriors and reproducers from Clone-group 1 had the highest frequency of wins, while individuals from Clone-group 3 had the least. No differences between tentacle density and acrorhagi density were observed. Tentacle length varied both across clone groups and between warriors and reproducers within colonies (warriors: P < 0.001, reproducers: P =0.004; and clone-group (CG) 1: P =0.001, CG 3: P = 0.003; respectively). Morphological characteristics measured do not appear to give a competitive advantage to individuals (P = 0.262). Aggressive ability seems to be conferred to the aggregation as a whole.