Colony Reproduction and Arboreal Life in the Ponerine Ant Gnamptogenys Menadensis (Hymenoptera: Formicidae)

COLONY REPRODUCTION AND ARBOREAL LIFE IN THE PONERINE ANT GNAMPTOGENYS MENADENSIS (HYMENOPTERA: FORMICIDAE) by B. GOBIN1, C. PEETERS2 and J. BILLEN1 (1 Laboratory of Entomology, University of Leuven, Naamsestraat 59, B-3000 Leuven, Belgium; 2CNRS URA 667 Laboratoire d'Ethologie Expérimentale et Comparée, Université Paris Nord, F-93430 Villetaneuse, France) ABSTRACT Gnamptogenys menadensis is an Indonesian ponerine ant that is exclusively arboreal. Foragers hunt for prey and sweet secretions on the branches and leaves of shrubs and trees, but never walk on the ground. It nests in pre-existing tree cavities which are sealed with a lining of organic material. Several factors facilitate colony reproduction by fragmentation: available nest sites are plentiful, nest structure represents only a minor investment of labour, and nests cannot be enlarged, inducing nest emigration or polydomy as colonies grow in size. A mechanism of colony fragmentation is one of the preadaptations to enable the replacement of queens by worker reproductives. We found that the majority of colonies (95%) in the studied population (Sulawesi) are queenless, and reproduce through gamergates (mated workers laying reproductive eggs). Nevertheless, queens can occasionally be produced, and 5% of nests contained a single reproductive queen. Due to obligate arboreal life, alate queen production seems to remain an infrequent strategy in addition to budding, since only independent founding queens can colonise new patches of vegetation. KEY WORDS: life history, gamergate, queen, nest emigration, budding, foraging, Ponerinae. INTRODUCTION All ants belonging to the subfamily Ponerinae are predators on arthropods, but other aspects of their ecological profile vary enormously. These mainly tropical ants nest in the ground or in rotting wood in the leaf litter stratum. Ponerine ants have conserved a great number of ancestral morphological traits (PEETERS, 1997). The queen-worker dimorphism is low, with little difference in the number of ovarioles between the two castes resulting in low queen fecundity and thus in small colony sizes (dozens to hundreds of