Voluntary Self-Sacrifice in Exploding Ants: a mechanism to defend co-evolved microbiomes?

By Associate Prof. Mag.rer.nat. Dr.rer.nat Irina Druzhinina
Vienna University of Technology

Project partners: Herbert Zettel, Natural History Museum Vienna
Rainer Schuhmacher, University of Natural Resources and Life Science Vienna

The mechanisms by which organisms compete for territory and resources are key processes in ecology. The carpenter ants in the Camponotus (Colobopsis) cylindricus complex (‘COCY’, or exploding ants), that dominate arboreal habitats in rain forests on Borneo, have evolved a so-far unique and remarkable behaviour: In territorial combat with enemy ants and other arthropods they sacrifice themselves by rupturing (autothysis) and releasing sticky and irritant contents of their hypertrophied mandibular glands to kill rivals.

Voluntary self-sacrifice is very rare in nature, undoubtedly due to attendant fitness losses. It is known in termites and honeybees, where effective deployment in defence of the nest may leave self-sacrificing workers with indirect fitness. Contrary to that, workers of COCY ants forage solitarily and explode during one-on-one confrontations far from nests. Thus they are defending the territory against potential competitors probably for continuously renewing food resources such as phyllosphere microbes. The hypothesis of this project is that autothysis of ants far from their nests is a mechanism employed by COCY ants to protect a specific microbiome that co-evolved with them and which they use for nutrition. For this purpose we will study evolution of COCY ants and phyllosphere microbiomes on their foraging grounds.

Our project will identify a new and major type of interaction between dominant rainforest insects, their associated microorganisms and plants.