The evolution of parasite virulence and host defences is affected bypopulation structure. This effect has been confirmed in studies focusing onlarge spatial scales, whereas the importance of local structure is not wellunderstood. Slavemaking ants are social parasites that exploit workers ofanother species to rear their offspring. Enslaved workers of the host speciesTemnothorax longispinosus have been found to exhibit an effectivepost-enslavement defence behaviour: enslaved workers were observed killing alarge proportion of the parasites' offspring. Since enslaved workers do notreproduce, they gain no direct fitness benefit from this 'rebellion' behaviour.However, there may be an indirect benefit: neighbouring host nests that arerelated to 'rebel' nests can benefit from a reduced raiding pressure, as aresult of the reduction in parasite nest size due to the enslaved workers'killing behaviour. We use a simple mathematical model to examine whether thesmall-scale population structure of the host species could explain theevolution of this potentially altruistic defence trait against slavemakingants. We find that this is the case if enslaved host workers are related tonearby host nests. In a population genetic study we confirm that enslavedworkers are, indeed, more closely related to host nests within the raidingrange of their resident slavemaker nest, than to host nests outside the raidingrange. This small-scale population structure seems to be a result of polydomy(e.g. the occupation of several nests in close proximity by a single colony)and could have enabled the evolution of 'rebellion' by kin selection.
展开▼
