The Genetic Architecture of Immune Defense and Reproduction in Male Bombus Terrestris Bumblebees

Abstract

Understanding the architecture of genetic variation, that is the number, effect, location, and interaction, of genes responsible for phenotypic variability in nature is important for the understanding of microevolutionary processes. In this study, we have used a quantitative trait loci (QTL) approach to uncover the genetic architecture of fitness-relevant traits associated with reproduction and immune defense in male Bombus terrestris bumblebees. Three male reproductive investment traits, the number and length of the produced sperm and the size of the accessory glands, were studied. Two branches of the insect innate immune system, the activation of the Phenoloxidase-cascade and the hemolymph's antibacterial activity, were investigated. We found that variation in most of the studied traits is based on a network of minor QTLs and epistatic interactions. Unexpectedly, there was no evidence for phenotypic or genetic trade-offs between the presumably costly investment in immune defense and reproductive effort in this population for the measured traits. In fact, we found a positive correlation, both, in phenotype and genetic architecture for the number of produced sperm and antibacterial activity against an insect pathogen. A major finding for all traits analyzed was that the epistatic interactions accounted for a major proportion of the explained phenotypic variance. Especially for traits involved in immune defense, this pattern highlights the possible role of parasites in the evolution and maintenance of recombination and sexual reproduction.

Host-parasite evolution in male-haploid hosts: an individual based network model

“…Lastly, when there was selection acting on the recombination rate the GA predicts higher recombination rates within haplodiploid hosts than diploid. This last result is supported by experimental findings of high recombination rates within haplodiploid species (Wilfert et al 2007;Meznar et al 2010;Stolle et al 2011). …”

“…These assessments will be done for both the matching allele model (MAM, infections occur when parasite genotypes match the host) and the Inverse MAM (IMAM, infections occur when parasite genotypes mismatch the host). In addition to this we will compare diplo-diploid with haplo-diploid (male-female) systems because the latter have been shown to have the highest recombination rates-in the animal kingdom (Meznar et al 2010;Stolle et al 2011;Wilfert et al 2007). The most divergent haplodiploid lineage is that of the Hymenoptera, an order that contains some of the most complex social systems with very tight network structures (Normark 2003).…”

Immunity in a variable world

“…In very rich environments, genetic correlations between physiologically linked traits may even become positive, as genetic variation for acquisition of resources from the environment becomes more prominent than variation for allocation of resources to competing traits (e.g. Reznick et al 2000;Barber et al 2001;Coltman et al 2001;Wilfert et al 2007). This is presumably the explanation for the above-mentioned positive correlation between antibacterial activity and sperm number observed by Wilfert et al (2007).…”

Cytonuclear Genic Incompatibilities Cause Increased Mortality in Male F2 Hybrids of Nasonia giraulti and N. vitripennis

“…Since there are no intralocus interactions in haploid males, alleles can easily be tested individually for their phenotypic effect in this sex. This significantly reduces the population sizes required to detect and map recessive alleles and epistatic loci in haploid F 2 hybrid males (Gadau et al 1999(Gadau et al , 2002Weston et al 1999;Wilfert et al 2007). The genetics of genic incompatibilities can easily be explored in the genus Nasonia, since interspecific F 1 hybrid females are viable and fertile while a certain percentage of their F 2 hybrid male offspring are not (Breeuwer and Werren 1995).…”