A shift in colony founding behaviour in the obligate plant-ant Crematogaster (Decacrema) morphospecies 2

Summary. A shift in colony founding behaviour from single queen (haplometrosis) to multiple queens (pleometrosis) was observed locally in the obligate plant-ant Crematogaster (Decacrema) morphospecies 2, which is associated with Macaranga trees in Borneo. In addition, about a quarter of all mature colonies (27 of 95 trees examined) were found to be multiple queen colonies. They arose either directly from pleometrotic founding colonies or secondarily by adoption of additional queens. Using microsatellite markers, we showed that queens in colonies founded through pleometrosis are unrelated and each queen participates in producing worker offspring, albeit with significant skew in a third of the colonies. In mature polygynous colonies, all resident queens contributed to the production of workers and sexual offspring. Relatedness of queens in mature polygynous colonies was not significantly higher than in foundress associations. We hypothesize that increased nest site limitation in this specific interaction trigger the observed shift in colony founding behaviour. Crematogaster msp. 2 inhabits the light demanding pioneer plant species Macaranga pearsonii that is typical for early successional stages of secondary forests. Thus suitable host-plants for colonisation are abundant for only a short time in highly disturbed sites and become increasingly sparse when secondary forest matures.Received 6 September 2004; revised 29 November; accepted 10 December 2004.