Genetic diversity, paternal origin and pathogen resistance in Cataglyphis desert ants

Group diversity is usually associated with a reduced risk of disease outbreak and a slower rate of pathogen transmission. In social insects, multiple mating by queens (polyandry) evolved several times although reducing workers inclusive fitness. One major hypothesis suggests that polyandry has been selected for to mitigate the risk of outbreak thanks to increased genetic diversity within colonies. We investigated this hypothesis in the ant Cataglyphis mauritanica, in which nestmate workers are produced by several clonal, single-mated queens. Using natural colonies, we correlated genetic diversity with worker survival to a fungal entomopathogen. We further tested whether workers from different paternal lineages (but a common maternal genome) show differential resistance in experimentally singleor multiple-patriline groups, and whether an increased number of patrilines in a group improved disease incidence. We show that workers from distinct patrilines vary in their resistance to pathogen in single-patriline colonies, but the difference among patrilines disappears when they are mixed in multiple-patriline colonies. Furthermore, pathogen resistance was affected by the number of patrilines in a group, with twoand three-patriline groups being more resistant than single-patriline groups. However, resistance did not differ between groups made of two and three patrilines; similarly, it was not associated with genetic diversity in natural colonies. Overall, our results suggest that collective disease defenses might homogenize workers resistance from different patrilines and, thereby, stabilize colony resistance.