Worker discrimination among queens in newly founded colonies of the fire ant Solenopsis invicta

Although colonies of the fire ant Solenopsis invicta are often founded by s mall groups of queens, all but one of the queens are soon eliminated due to worker attacks and queen fighting. The elimination of supernumerary queens provides an important context for tests of discrimination bq the workers, since the outcome of these interactions strongly affects the workers' inclu sive fitness, To test whether workers in newly founded colonies discriminat e among nestmate queens, paired co-foundresses were narrowly separated by m etal screens that prevented direct fighting, but through which the workers could easily pass. Soon after the first workers completed development, they often attacked one of the queens: these attacks were strongly associated w ith queen mortality. When one queen's brood was discarded, so that the adul t workers were all the daughters of just one queen, the workers were signif icantly less likely to bite their mother than the unrelated queen: however, this tendency was comparatively weak. Queens kept temporarily at a higher temperature to increase their rate of investment in brood-rearing lost weig ht more rapidly than paired queens and were subsequently more likely to be attacked and killed by workers. Workers were more likely to bite queens tha t had been temporarily isolated than queens that remained close to brood an d workers. When queens were not separated by screens, the presence of worke rs stimulated queen fights, These results show that workers discriminate st rongly among equally familiar queens and that discrimination is based more on the queens' condition and recent social environment than on kinship.