ROLE OF FAMILIARITY IN STRUCTURING MALE-MALE SOCIAL INTERACTIONS IN THE COCKROACH GROMPHADORHINA-PORTENTOSA (DICTYOPTERA, BLABERIDAE)

We examined the influence of prior social experience on the outcome of agonistic interactions between male Madagascar hissing cockroaches, Gromphadorhina portentosa (Schaum). Males were placed randomly in pairs and allowed to form stable dominance-subordinance associations (original pairs). Two types of social conditions were then examined. Treatment pairs were composed of either familiar males (the males were re-paired with the same male that they had interacted with previously) or unfamiliar individuals (males were paired with a male that they had not interacted with previously). Males in familiar pairs maintained their rank during subsequent interactions. However, males in unfamiliar pairs lost their rank, indicating that familiarity of the opponent and not past experience of winning or losing an encounter determined the outcome of interactions. We also compared the behavior of individual males in the treatment groups with their behavior in the original pairings. Previously dominant males decreased their levels of aggression and hissed less when interacting with unfamiliar opponents. Previously subordinate males were more aggressive and hissed more in unfamiliar pairs. As a result, overall levels of behavior displayed in pairs of males did not differ. Aggression and hissing appear to be important in the maintenance, rather than the establishment, of relationships between G. portentosa males. We also discuss the possibility that agonistic hissing functions in individual discrimination rather than as a status cue.