02574nas a2200253 4500008004100000022001400041245009400055210006900149260001600218300002400234490000800258520176700266653002302033653003302056653002702089653002702116653002502143653001402168100001502182700001902197700001602216700001402232856007402246 2015 eng d a0962-845200aAnti-pathogen protection versus survival costs mediated by an ectosymbiont in an ant host0 aAntipathogen protection versus survival costs mediated by an ect cOct-01-2016 a20141976 - 201419760 v2823 a

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 ectosymbiontLaboulbenia 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 underMetarhizium 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.

10agrooming behaviour10ahost–parasite interactions10aimmune gene expression10aLaboulbenia formicarum10aMetarhizium brunneum10asymbiosis1 aKonrad, M.1 aGrasse, A., V.1 aTragust, S.1 aCremer, S uhttp://rspb.royalsocietypublishing.org/cgi/doi/10.1098/rspb.2014.1976