Abstract
Ant queens often associate to found new colonies, yet the benefits of this behaviour remain unclear. A major hypothesis is that queens founding in groups are protected by social immunity and can better resist disease than solitary queens, due to mutual grooming, sharing of antimicrobials, or higher genetic diversity among their workers. We tested this hypothesis by manipulating the number of queens in incipient colonies of Lasius niger and measuring their resistance to the fungal entomopathogen Metarhizium brunneum. We found no evidence for social immunity in associations of founding queens. First, co-founding queens engaged in self-grooming, but performed very little allo-grooming or trophallaxis. Second, co-founding queens did not exhibit higher pathogen resistance than solitary queens, and their respective workers did not differ in disease resistance. Finally, queens founding in groups increased their investment in a component of individual immunity, as expected if they do not benefit from social immunity but respond to a higher risk of disease. Overall, our results provide no evidence that joint colony founding by L. niger queens increases their ability to resist fungal pathogens.
Highlights
In social insects, founding novel colonies is a risky enterprise
A major potential benefit of joint colony founding by ant queens is increased disease resistance, which might stem from various mechanisms conferring social immunity[5,6]
If ant queens in associations profit from social immunity, we predict that co-founding queens will (i) show higher resistance to the fungal pathogen than solitary queens, (ii) engage in allo-grooming, Department of Ecology and Evolution, Biophore, UNIL-Sorge, University of Lausanne, 1015, Lausanne, Switzerland
Summary
In social insects, founding novel colonies is a risky enterprise. Many ant species produce massive numbers of queens that fly away from their natal nest, mate, and seek to establish colonies independently[1,2]. A major potential benefit of joint colony founding by ant queens is increased disease resistance, which might stem from various mechanisms conferring social immunity[5,6]. If joint colony founding confers social immunity, the queens may decrease their investment in energetically costly individual immunity[14] Such a trade-off has been documented in wood ants, who showed lower activation of their immune system when antimicrobial resin was present in their nests[15]. In absence of social immunity, queens in groups are likely to increase individual immunity in order to respond to higher disease risk[16,17,18]. If ant queens in associations profit from social immunity, we predict that co-founding queens will (i) show higher resistance to the fungal pathogen than solitary queens, (ii) engage in allo-grooming, www.nature.com/scientificreports/
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