EFFECTS OF SOCIAL-ORGANIZATION ON INTER-CLONAL DOMINANCE RELATIONSHIPS IN THE SEA-ANEMONE, ANTHOPLEURA-ELEGANTISSIMA

In the sea anemone Anthopleura elegantissima contact between non-clone mates often elicits inter-clonal fighting, involving the application o f nematocyst-laden fighting tentacles (acrorhagi) and the locomotory r etreat of losing polyps. This study confirms that isoclonal aggregatio ns of A. elegantissima display an inducible polymorphism, such that po lyps at the inter-clonal boundaries (warriors) are typically smaller a nd carry more fighting tentacles (acrorhagi) than more central (reprod uctive) polyps. Based on the outcomes of eight separate contests betwe en each combination of like and unlike morphs for each of seven pairs of neighbouring clones (i.e. N = 224 contests), this study provides th e first direct evidence that warriors are aptly named. All sets of nei ghbouring warriors and reproductives were mutually aggressive, and war riors, despite their overall size disadvantage, won 41 out of 81 conte sts with the reproductive polyps of their neighbouring clone. In addit ion, warrior and reproductive polyps were almost equally likely to ini tiate an attack and to retaliate. Thus, the success of warriors agains t the typically far larger reproductive polyps primarily reflects the proportionately greater allocation by warriors of resources to acrorha gi. The outcomes of the inter-clonal contests further indicate that pa irs of neighbouring clones are unevenly matched in terms of their figh ting ability, and that inter-clonal dominance is again largely determi ned by relative allocation of resources to acrorhagi. In five of seven inter-clonal combinations the warriors of the apparently dominant clo ne defeated the majority of opposing warriors (in three cases winning all eight contests). This result represents an apparent paradox, as ea rlier work showed that inter-clonal borders may persist for several ye ars. Further work is needed to determine the extent to which agonistic behaviour determines the outcomes of inter-clonal competition for spa ce and whether the outcomes of contests between pairs of individuals r eflect the true dominance relationships of entire clones. (C) 1996 The Association for the Study of Animal Behaviour