title: Anti-pathogen protection versus survival costs mediated by an ectosymbiont in an ant host.
abstract: The fitness effects of symbionts on their hosts can be context-dependent, with usually benign symbionts causing detrimental effects when their hosts are stressed, or typically parasitic symbionts providing protection towards their hosts (e.g. against pathogen infection). Here, we studied the novel association between the invasive garden ant Lasius neglectus and its fungal ectosymbiont Laboulbenia formicarum for potential costs and benefits. We tested ants with different Laboulbenia levels for their survival and immunity under resource limitation and exposure to the obligate killing entomopathogen Metarhizium brunneum. While survival of L. neglectus workers under starvation was significantly decreased with increasing Laboulbenia levels, host survival under Metarhizium exposure increased with higher levels of the ectosymbiont, suggesting a symbiont-mediated anti-pathogen protection, which seems to be driven mechanistically by both improved sanitary behaviours and an upregulated immune system. Ants with high Laboulbenia levels showed significantly longer self-grooming and elevated expression of immune genes relevant for wound repair and antifungal responses (β-1,3-glucan binding protein, Prophenoloxidase), compared with ants carrying low Laboulbenia levels. This suggests that the ectosymbiont Laboulbenia formicarum weakens its ant host by either direct resource exploitation or the costs of an upregulated behavioural and immunological response, which, however, provides a prophylactic protection upon later exposure to pathogens.
authors.affiliation: Evolutionary Biology, IST Austria (Institute of Science and Technology Austria), Am Campus 1, Klosterneuburg 3400, Austria.
authors.forename: Matthias
authors.initials: M
authors.lastname: Konrad
authors.affiliation: Evolutionary Biology, IST Austria (Institute of Science and Technology Austria), Am Campus 1, Klosterneuburg 3400, Austria.
authors.forename: Anna V
authors.initials: AV
authors.lastname: Grasse
authors.affiliation: Evolutionary Biology, IST Austria (Institute of Science and Technology Austria), Am Campus 1, Klosterneuburg 3400, Austria Evolution, Genetics and Behaviour, University of Regensburg, Universitätsstrasse 31, Regensburg 93040, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Tragust
authors.affiliation: Evolutionary Biology, IST Austria (Institute of Science and Technology Austria), Am Campus 1, Klosterneuburg 3400, Austria sylvia.cremer@ist.ac.at.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Cremer
mesh_terms: D000818:Animals; D001000:Ants / Q000276:immunology / Q000382:microbiology*; D001203:Ascomycota / Q000502:physiology*; D001522:Behavior, Animal; D006120:Grooming; D054884:Host-Pathogen Interactions; D013559:Symbiosis
keywords: Laboulbenia formicarum; Metarhizium brunneum; grooming behaviour; host–parasite interactions; immune gene expression; symbiosis