Intraspecific aggression in the colour morphs of the anemone Phymactis clematis from Chile

The anemone Phymactis clematis exhibits intraspecific agression. An investigation into dominance relationships amongst the 3 colour morphs collected from Vna del Mar, Chile, during June, 1980, revealed them to be equally aggressive. The outcomes of experimental contests appeared to reside solely with size-dependent differences in the threshold for the release of agression. Contests were asymmetric and larger individuals displayed aggression earlier against smaller opponents, and won encounters. An analysis of times for the onset of aggression in contests showed that they were highly variable and were not a good indicator of the absolute aggressive ability of individuals as denoted by dominance rankings. It provided, however, evidence indicating a lack of assessment of opponent size during initial contact. This is discussed in relation to the evolution of aggression in anemones and to the concept of evolutionarily stable strategies in contest behaviour. It is concluded that future work on the apparent size-dependent threshold will most instructively be conducted at the neurophysiological level.