Pheromones involved in aggressive behaviour in the ant, Myrmecia gulosa

Abstract

It is shown that the characteristic aggressive behaviour of Myrmecia gulosa, a member of the most primitive and generalized subfamily of living ants, follows a more complex pattern than in advanced Formicidae. Aggressive behaviour is examined by means of a three-pronged experimental approach, in which a high level of discrimination between reactions is obtained through analysing a number of quantitative factors instead of only one, and analysing them both independently and in combination. Two categories of aggression are demonstrated. In the first, workers, acting as solitary foragers, behave aggressively towards the prey they capture as food for the brood. They attack under the influence of visual, odour, and tactile stimuli emanating from the prey itself. In the second, workers acting collectively, behave aggressively to protect the nest territory under the influence of a complex of pheromones produced by their nest mates. The pheromone complex controlling territorial aggression in M. gulosa includes a low-level alarm pheromone in the rectal secretion increasing alerting, a second alarm pheromone in Dufour's gland secretion effective as an activation stimulus, and a separate attack pheromone secreted by the mandibular glands. The results represent the first records of pheromone production in the Myrmeciinae, the first occasion in the Formicidae on which a rectal pheromone has been implicated in aggression, and the first instance of mandibular glands producing an ‘attack’ pheromone separate and distinct from that evoking ‘alarm’. Consideration is given to the light thrown by the study on the evolution of social ‘alarm’ in the Formicidae, from its minor position in the lower ants as the initial facet of the aggression pattern, to its dominance over the defensive behaviour of the higher ants.