No Evidence for Immune Priming in Ants Exposed to a Fungal Pathogen

Abstract

There is accumulating evidence that invertebrates can acquire long-term protection against pathogens through immune priming. However, the range of pathogens eliciting immune priming and the specificity of the response remain unclear. Here, we tested if the exposure to a natural fungal pathogen elicited immune priming in ants. We found no evidence for immune priming in Formica selysi workers exposed to Beauveria bassiana. The initial exposure of ants to the fungus did not alter their resistance in a subsequent challenge with the same fungus. There was no sign of priming when using homologous and heterologous combinations of fungal strains for exposure and subsequent challenges at two time intervals. Hence, within the range of conditions tested, the immune response of this social insect to the fungal pathogen appears to lack memory and strain-specificity. These results show that immune priming is not ubiquitous across pathogens, hosts and conditions, possibly because of immune evasion by the pathogen or efficient social defences by the host.

Thermal and physical stresses induce a short-term immune priming effect in Galleria mellonella larvae

“…Immune priming can also be affected by the social interaction and behaviour of challenged bees (Richard et al, 2008). Immune priming in Formica selysi workers following challenge with Beauveria bassiana is short term (Reber and Chapuisat, 2012) raising the possibility that colony living precludes the necessity of having a prolonged immune priming effect as other compensatory mechanisms may be operating in the colony. For example, in honey bee colonies an elevated nest temperature is generated as a colony-level response to prevent chalk brood (Starks et al, 2000).…”

“…The relatively short duration of the immune priming effect in Galleria may be due to the fact that in its normal habitat G. mellonella live in bee colonies where the high temperature may offer some degree of protection against pathogens thus not necessitating a long term, heightened immune response that may be metabolically costly to maintain. In contrast to other insects, ants do not show immune priming when challenged with B. bassiana and it has been suggested that behavioral or group level chemical defences may limit infection and thus remove the necessity for an immune priming response (Reber and Chapuisat, 2012). The observation of a short term (24 h) immune priming effect in G. mellonella larvae is of interest in that it may have evolved as a response to life within the colony of another insect.…”

Evidence for Specific Genotype-Dependent Immune Priming in the Lophotrochozoan <b><i>Biomphalaria glabrata</i></b> Snail

“…Several studies have found evidence for (insects, crustaceans) [2,14,22,23,24] and others have failed to detect (insects) [3,25,26] immune priming in invertebrates. Thus it is difficult to conclude whether priming is universal, restricted to several invertebrate groups or species, or to specific host/parasite combinations.…”

Immune-priming in ant larvae: social immunity does not undermine individual immunity

“…Yet, determining the developmental stage during which social insects start exhibiting immunological defences, some of which are analogous to the vertebrate adaptive immune systems [20], may shed light on the relation and potential trade-offs between inherent individual-level immune responses and the insect's social milieu. Previous studies have reported on the effect of age on immune maturation in several honeybee and ant species [13][14][15][16]. Unfortunately, given the confounding effects of division of labour, its associated pathogenic risks and immune senescence on disease susceptibility, the selective pressures and factor(s) fashioning immune responses of young versus old workers remain elusive.…”