Mechanisms regulating functional monogyny in a Japanese population of Leptothorax acervorum (Hymenoptera, Formicidae): dominance hierarchy and preferential egg cannibalism

Queen behaviour of Leptothorax acervorum collected in northern Japan was observed in four functionally monogynous colonies (one functional mated egg-laying queen with some supernumerary mated but sterile queens) and two monogynous colonies with some virgin queens. In three functionally monogynous colonies, dominance behaviour including antennation, biting, pulling, and remarkable avoidance where queens fled approaching the functional queens, were frequently observed among queens. In two of the three colonies, an almost linear dominance hierarchy was established among queens and only the top ranked queen laid eggs. However, the hierarchy was not stable : in one colony the queens in second and third ranks and the second ranked queen in the other colony were expelled from colonies. Such queen antagonism was very rare in the other functionally monogynous colony, where workers expelled the fertile queen, and the other queen replaced the egg-layer. In monogynous colonies with virgin queens, virgin queens showed worker-like behaviour, and dominance interactions completely lacked among queens. Oophagy was often observed among nestmates : this always Occurred just after oviposition. Eggs of functional queens were not eaten while most eggs laid by Supernumerary queens were eaten by functional queens and workers. Supernumerary queens never showed oophagy. Workers laid trophic eggs and reproductive eggs : the former ones were always eaten while one third of the latter survived.