Lack of inbreeding avoidance in the Argentine ant Linepithema humile

Although workers might increase their inclusive fitness by favoringcloser over more distant kin, evidence suggest that nepotismgenerally does not occur within colonies of social insects.It has been suggested that this may be due to the cost of recognitionerrors. We tested whether recognition occurs in a system wherea better than random ability to recognize kin should be selected for. Using DNA microsatellites, we show that sexuals of theArgentine ant Linepithema humile fail to use genetic cues toavoid sib-mating. When offspring of two queens were allowedto mate, the percentage of matings among siblings was not significantlylower than expected under the hypothesis of random mating.The finding that sexuals fail to use genetic cues to avoid sib-matings cannot be attributed to the cost of recognitionerrors because any recognition system that would lead to abetter than random ability to avoid sib-mating should be selectedfor when there are costs to inbreeding. These data are thusconsistent with the view that kin recognition mediated solelyby genetic cues might be intrinsically error prone within coloniesof social insects.