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

Abstract

Background: Understanding 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. Results: Our 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 a general reduction 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. Conclusions: Our 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 effect of intrinsic physiological traits on diapause survival and their underlying mechanisms in an annual bee speciesBombus impatiens

“…Together with findings from other studies, these data show that shifts in queens’ physiological quality, as well as the interaction between nutritional status and age ( Costa et al ., 2020 ), may influence diapause survival. While the queens in our study were unmated ( Baer et al , 2005 , Colgan et al , 2019 ), previous research in B. terrestris queens found that, on average, unmated queens survived only 5 days longer as compared to mated queens in cold storage ( Greeff et al ., 2008 ). Therefore, the lack of mating is unlikely to significantly affect our data on queen survival.…”

“…Both types of proteins are critical for dealing with stressors associated with diapause, such as cold stress and starvation. However, a more detailed analysis of the proteins present in the hemolymph pre-diapause [see ( Colgan et al ., 2019 )] could be informative to understanding which stressors queens are equipped to mitigate during diapause (e.g. temperature stress or pathogens) and which stressors are more likely to result in queen mortality.…”

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 ].…”

Parasite resistance and immunity across female castes in a social insect

“…However, post-hibernation they face significant exposure as they forage for resources before and while founding their colony. Interestingly, mating and hibernation drive changes in gyne immunity (Barribeau and Schmid-Hempel 2017;Colgan et al 2019) and gut microbiome (Wang et al 2019), both of which could influence interactions between gynes and C. bombi. Further work should examine their susceptibility to infection, in comparison to gynes, and its relation to immunity.…”