Kaur R , Stoldt M, Jongepier E , Barbara Feldmeyer B, Bornberg-Bauer E ,Susanne Foitzik S
Attack or no attack – Ant behaviour and brain gene expression of defending hosts depend on the ecological success of the intruding social parasite
Transact Royal Soc, Lond B, 2018

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The geographic mosaic theory of coevolution predicts that species interactions vary between locales. Depending on who leads the coevolutionary arms-race, the effectivity of parasite attack or host defence strategies will explain parasite prevalence. Here, we compare behaviour and brain transcriptomes of Temnothorax longispinosus ant workers when defending their nest against an invading social parasite, the slavemaking ant T. americanus. A full-factorial design allowed us to test whether behaviour and gene expression is linked to parasite pressure on host populations or to the ecological success of parasite populations. We found parasite success to be much more important, albeit host defences were shown before to co-vary with local parasite pressure. Our behavioural analyses revealed that parasites from more successful populations were less often attacked by hosts and this association was further supported by gene expression analysis. Our study indicates that host-parasite interactions are strongly influenced by the social parasites’ behavioural or chemical strategies, so that variation in parasite prevalence is determined by parasite traits rather than the efficacy of host defence. Gene functions associated with parasite success indicated strong neuronal responses in hosts, including long-term changes in gene regulation, such as histone deacetylation, indicating an enduring impact of parasites on host behaviour.