Mating precedes selective immune priming which is maintained throughout bumblebee queen diapause

Abstract

BackgroundUnderstanding the mechanisms by which organisms adapt to unfavourable conditions is a fundamental question in ecology and evolutionary biology. One such mechanism is diapause, a period of dormancy typically found in nematodes, fish, crustaceans and insects. This state is a key life-history event characterised by arrested development, suppressed metabolism and increased stress tolerance and allows an organism to avoid prolonged periods of harsh and inhospitable environmental conditions. For some species, diapause is preceded by mating which can have a profound effect on female behaviour, physiology and key biological processes, including immunity. However, our understanding of how mating impacts long-term immunity and whether these effects persist throughout diapause is currently limited. To address this, we explored molecular changes in the haemolymph of the ecologically important pollinator, the buff-tailed bumblebee Bombus terrestris. B. terrestris queens mate prior to entering diapause, a non-feeding period of arrested development that can last 6–9 months. Using mass-spectrometry-based proteomics, we quantified changes in the pre-diapause queen haemolymph after mating, as well as the subsequent protein expression of mated queens during and post-diapause.ResultsOur analysis identified distinct proteome profiles associated with diapause preparation, maintenance and termination. More specifically, mating pre-diapause was followed by an increase in the abundance of antimicrobial peptides, key effectors of the immune system. Furthermore, we identified the elevated abundance of these proteins to be maintained throughout diapause. This finding was in contrast to the general reduction observed in immune proteins during diapause suggestive of selective immune priming and expression during diapause. Diapause also affected the expression of proteins involved in cuticular maintenance, olfaction, as well as proteins of unknown function, which may have roles in diapause regulation.ConclusionsOur results provide clear molecular evidence for the consequences and benefits of mating at the immune level as it precedes the selective increased abundance of antimicrobial peptides that are sustained throughout diapause. In addition, our results provide novel insights into the molecular mechanisms by which bumblebees prepare for, survive, and recover from diapause, insights that may have implications for our general understanding of these processes in other insect groups.

The Importance of Males to Bumble Bee (Bombus Species) Nest Development and Colony Viability

“…There is also evidence that mating may also influence the immune system of queens. Molecular evidence has suggested that mating prior to overwintering for B. terrestris resulted in elevated levels of antimicrobial peptides, and these peptide levels were maintained throughout overwintering [112]. Conversely, comparisons between virgin and mating queens have found that mating significantly increases the incidence of melanized spermatheca, which may indicate pathogen transfer during mating [111].…”

Integrative Proteomic and Phosphoproteomic Analyses Revealed Complex Mechanisms Underlying Reproductive Diapause in Bombus terrestris Queens

“…There have been several studies of the transcriptome and proteome of the different diapause stages of B. terrestris . Comparative analyses indicated that diapause in bumblebees is associated with nutrient storage, core metabolic pathways, stress resistance, insect hormone biosynthesis, and proteins involved in cuticle maintenance [ 37 , 38 , 39 ]. In the current study, comparisons of the protein expression profiles during the three stages of diapause were performed using TMT-labeled proteomics to expand the current understanding of changes at the phosphorylation level.…”

“…Key proteins involved in neuroactive ligand–receptor interactions and the glutamatergic synapse pathway related to glutamate neurotransmission were upregulated in early diapause in the female red spider mite ( Tetranychus urticae ) [ 41 ]. The expression levels of glutamate decarboxylase, which plays a role in neurotransmitter synthesis, were increased in the hemolymph of bumblebee queens at 48 h compared to 6 h postdiapause [ 39 ]. In this study, many genes associated with neurotransmitter synthesis were regulated at both the protein and phosphorylation levels during different stages of diapause.…”

Hormonal Regulation of Reproductive Diapause That Occurs in the Year-Round Mass Rearing of Bombus terrestris Queens

“…The integrated mRNA and protein level data revealed different levels regulated adult reproductive diapause that occurs in the year-round mass rearing of B. terrestris , and our results suggested that ILPs and JH III played some important roles in the reproductive diapause of queens. Together with results from other related research, , we proposed a model to explain the regulation of reproductive diapause in B. terrestris during the year-round mass rearing process (Figure ). This work could thus facilitate a better understanding of reproductive diapause in the ecologically and economically important pollinators of the world.…”