EXPERIMENTALLY-INDUCED DIGYNY IN POLISTES-GALLICUS L WASP COLONIES - COMPARISONS WITH POLISTES-DOMINULUS CHRIST

We analysed the social and reproductive behaviours of two Polistes spe cies, the usually monogynous P. gallicus and the potentially polygynou s P. dominulus, in laboratory cages. We induced digynic associations i n both species in order to investigate the proximal factors responsibl e for the differences in reproductive strategies and to determine whic h traits were involved in the change-over from the one type of nest fo undation to the other in the course of evolution. In both species, an encounter between two reproductive females led to a fight ending in ei ther the flight or the submission of one of the wasps and then, in the latter case, in the establishment of a two-females-founding nest. Enc ounters on a well developed nest led to violent fighting in P. gallicu s, sometimes ending in death or mutilation, while joining a nest initi ated by another female was possible in P. dominulus. The relationships between associated foundresses were clearly of the dominance/subordin ation type in both species. Some behavioural differentiation accompani ed the hierarchical organization. However, subordinate wasps of P. gal licus were able to perform both dominance behaviour and oophagy, which usually occur in the dominant individuals. This refusal of the subord inate role sometimes led to the decline of the brood, and of the colon y itself. When placed in a multi-foundress situation, a monogynous spe cies such as P. gallicus shows behaviour which is intermediate between strictly territoriality and a truly polygynous behaviour. In the norm al conditions of the species life, this intermediate behaviour cannot be said to be an evolutionarily stable strategy because it is accompan ied by mutual, lasting differential oophagy that results in a decrease in the production of descendants.