Innate expression of antimicrobial peptides does not explain genotypic diversity in resistance to fungal brood parasites in the honey bee

Abstract

-The genetic basis of host resistance to parasites is a fundamental aspect of host-parasite co-evolution, yet the precise mechanisms often remain unclear. Here, we follow on from a previous study on the genetically mediated variation in resistance to two common fungal brood parasites that cause chalkbrood and stonebrood in the honey bee. We assessed whether genetically mediated variation in resistance can be explained by the baseline immunocompetence of different larval genotypes by correlating the constitutive expression of two key immune genes with the observed level of resistance of each larval genotype to four different fungal brood parasites. We found significant variation between larval genotypes in the constitutive expression of abaecin but not defensin 2 , but despite a suggestion of negative correlations between gene expression and resistance level in older larvae, there was no consistent evidence that baseline abaecin expression is a relevant predictor of resistance to these parasites. These results suggest that the constitutive expression of abaecin appears to have a genetic basis in honey bee larvae but that mechanisms other than innate expression of antimicrobial peptides might be more important in defence against the specific fungal brood parasites assessed here.Apis mellifera / abaecin / defensin / antimicrobial peptide / Ascosphaera apis / Aspergillus flavus

Genetic diversity confers colony-level benefits due to individual immunity

“…Since a high constitutive production of antimicrobial peptides can have costs for both individuals and colonies [13,16], selection may favour inducible expression rather than constitutive expression. A recent study has in fact shown that constitutive expression does not seem to correlate with subsequent ability to fight pathogen exposure [22], which supports the findings presented here. The mechanism explaining intracolonial variance of immune expression could be explained by differing response thresholds, whereby some larvae are able to respond more quickly or more strongly to pathogens and thus show higher levels of immune gene expression after a challenge.…”

Dietary amino acid and vitamin complex protects honey bee from immunosuppression caused by Nosema ceranae

“…The results obtained for abaecin gene might be discussed in light of previous reports about genetic variation in expression of abaecin [ 65 – 67 ]. Besides, Evison et al [ 68 ] found significant variation in expression levels of abaecin between bee patrilines. These reports enable us to justify our results obtained for abaecin gene expression, the more so we could not influence the paternity of bees in our experiment.…”

Between‐population differences in constitutive and infection‐induced gene expression in threespine stickleback

“…This can happen, for instance, if one population consistently has higher numbers of certain types of immune cells, leading to higher tissue‐level expression of genes unique to that cell type. Numerous studies have documented variation in constitutive immunity as a driver of variation in response to parasites or pathogens (Ali et al, 2012; Evison et al, 2016; Kamiya et al, 2016; Schmitt et al, 2013). For example, genotypes of potato with higher resistance to the pathogen Phytophthora are characterized by increased constitutive expression of immune defences (Ali et al, 2012).…”

“…Numerous studies have documented variation in constitutive immunity as a driver of variation in response to parasites or pathogens (Ali et al, 2012;Evison et al, 2016;Kamiya et al, 2016;Schmitt et al, 2013). For example, genotypes of potato with higher resistance to the pathogen Phytophthora are characterized by increased constitutive expression of immune defences (Ali et al, 2012).…”