Aggression versus courtship in threespine sticklebacks and the role of habituation to neighbours

Interaction of courtship and territorial aggression in male threespine sticklebacks, Gasterosteus aculeatus, was investigated by presenting dummy females to subjects nesting alone (solitary situation) and in view of males nesting in adjacent tanks (rival situation). During dummy presentation subjects engaged in more courtship and nest activity when solitary than when in the rival situation. Behaviour of subjects in the latter situation was dominated by threats and attempts to bite rivals during dummy presentation. Thus, rivals can interfere with another male's courtship by competing for the time during which he could court a female or by eliciting in him an aggressive state that is incompatible with sexual behaviour. Subjects in the rival situation gradually decreased the time spent with rivals but increased the time spent courting the dummy and tending the nest during presentations. This decrease in aggression towards neighbouring males is presumed to result from habituation. Thus, habituation can play an important role in mitigating the aggressive response to familiar rivals, allowing males to devote more time and energy to courtship and nest activities while still forming breeding aggregations in which members may mutually benefit.