Individual and collective decision making and risk evaluation in slavemaking ants

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Colonies of social insects are prime examples for cooperative decision making and collective intelligence. In contrast to the organisation of human societies where decisions are often made by one or few specially assigned individuals, decisions in ant societies are based on simple rules of thumb, heeded by each ant. For this kind of decentralized processes to work, all individuals must have access to relevant information to make adaptive decisions. Slavemaking ants are obligate social parasites that completely rely upon their slaves, allospecific workers, for all routine colony tasks. Their reproductive success and thus the fitness of a social parasite colony directly depend on the number of slaves found in a parasite colony. Slaves are obtained via regular slave raids, which are in itself risky tasks for the slavemakers: around 10% of the parasite workers involved in a raid are severely injured or killed during the process. The decision which host colony to attack is so crucial and scout ants searching for new host colonies should weigh risks and benefits carefully before recruiting nest mates for an attack. Earlier studies showed that parasite colonies - when given a choice - indeed prefer to attack colonies of less well defended host species and adjust the number of parasite workers in a raiding party to victim host nest size. Here, we plan to investigate risk evaluation and decision making in two slavemaking ant species, which represent independent origins of slavery and differ in average colony size. We want to focus on individual decisions made by scout ants and on collective ones of parasite colonies on whether or not to initiate an attack on a given host nest. Important for these decisions are information on the potential victim colony and on the condition of the parasite colony, which has to be obtained, distributed and evaluated by parasite colony members.