“Hedgehog-ants” protected against a pathogen

In this week’s issue of the Proceedings of the Royal Society B Sylvia Cremer and her team describe for the first time the immunoprotective effect of an association of ants with an ectosymbiotic fungus, that gives the ants a “hedgehog-like” appearance. In their work “Anti-pathogen Protection versus Survival Costs mediated by an Ectosymbiont in an Ant Host”, Konrad et al. studied the novel association between the invasive garden ant and the fungal ectosymbiont Laboulbenia, which have both been recently introduced to Europe. The invasive garden ant quickly spreads throughout Europe and several of its populations now carry the Laboulbenia fungus, whose fruiting bodies anchor in the ant’s body surface, giving it “hedgehog resemblence”. The researchers found that ants with higher levels of the fungal ectosymbiont suffer higher mortality under food restriction, but on the upside are more resistant against infection by a common and deadly insect disease, the green muscardine. This protective effect is likely caused by a stimulation of both the ants’ hygiene behavior (increased selfgrooming) and their immune system (upregulation of immune gene expression). A lower susceptibility to this common and deadly disease may add to the success of the invasive garden ants.

In her recent review article “Individual and social immunization in insects” in a special issue of Trends in Immunology on Pathogen Avoidance, Resistance and Tolerance, Cremer and her postdoc Leila Masri gave an overview of the recent findings on such protective immunization of insects, as in the case of garden ants and Laboulbenia fungus. Masri and Cremer review recent evidence for and insights into the mechanisms underlying immunization in insects, which can be triggered either by a previous pathogen exposure of the same individual, or – in social species like ants and bees – by an exposed nest mate (individual vs social immunization). The researchers disentangle general immunoprotective effects from specific immune memory (known as priming) and examine immunization both within the lifetime of an individual or a colony and across generations to the benefit of the offspring. They conclude that recurrent parasitic threats have shaped the evolution of both the individual immune systems and colony-level social immunity in insects.