Aggressive Motivation in the Midas Cichlid: Evidence for Behavioral Efference

Behavioral Efference is a hypothetical positive feedback from the performance of an aggressive display that augments the level of aggressive motivation. The hypothesis was proposed (Bond, 1989) to account for the occurrence of truthful communication during aggressive encounters, even in the face of a presumed selective pressure in favor of deceit (Maynard Smith, 1984). Evidence of Behavioral Efference was sought in an experimental study of adult Midas cichlids Cichlasoma citrinellum, in which subjects responded aggressively to varying sizes of dummy fish. Before and after each aggression trial, the level of aggressive motivation was estimated from the intensity of the subject’s attacks on conspecific juveniles. A weighted index of aggressiveness that objectively combined the frequencies of four aggressive action patterns was obtained using detrended correspondence analysis. Aggression indices from aggression trials, as well as from intertrial intervals, furnished a basis for comparison of two causal models: behavioral efference, which assumes that post-stimulus motivation is substantially influenced by display performance, and Direct Stimulus Mediation, which assumes that the displays themselves play no immediate causal role. When the subjects actively displayed to the stimulus dummy, the results showed no significant correlation between the size of the dummy and the magnitude of the motivational effect. However, a significant relationship was demonstrated between the level of aggressive display and subsequent increases in aggressive motivation, in precise accord with the Behavioral Efference model. Direct Stimulus Mediation was evident only in trials in which the subject displayed no overt aggression toward the stimulus object. An account of the functional significance of Behavioral Efference is provided, suggesting that the feedback serves to regulate the intensity of aggressive interactions by preparing the displaying individual for active combat.