Testing the effect of paraquat exposure on genomic recombination rates in queens of the western honey bee, Apis mellifera

Potassium ion channels as a molecular target to reduce virus infection and mortality of honey bee colonies

Declines in managed honey bee populations are multifactorial but closely associated with reduced virus immunocompetence and thus, mechanisms to enhance immune function are likely to reduce viral infection rates and increase colony viability. However, gaps in knowledge regarding physiological mechanisms or 'druggable' target sites to enhance bee immunocompetence has prevented therapeutics development to reduce virus infection. Our data bridge this knowledge gap by identifying ATP-sensitive inward rectifier potassium (KATP) channels as a pharmacologically tractable target for reducing virus-mediated mortality and viral replication in bees, as well as increasing an aspect of colony-level immunity. Bees infected with Israeli acute paralysis virus and provided KATP channel activators had similar mortality rates as uninfected bees. Furthermore, we show that generation of reactive oxygen species (ROS) and regulation of ROS concentrations through pharmacological activation of KATP channels can stimulate antiviral responses, highlighting a functional framework for physiological regulation of the bee immune system. Next, we tested the influence of pharmacological activation of KATP channels on infection of 6 viruses at the colony level in the field. Data strongly support that KATP channels are a field-relevant target site as colonies treated with pinacidil, a KATP channel activator, had reduced titers of seven bee-relevant viruses by up to 75-fold and reduced them to levels comparable to non-inoculated colonies. Together, these data indicate a functional linkage between KATP channels, ROS, and antiviral defense mechanisms in bees and define a toxicologically relevant pathway that can be used for novel therapeutics development to enhance bee health and colony sustainability in the field.

Social organization and the evolution of life-history traits in two queen morphs of the ant Temnothorax rugatulus

During the evolution of social insects, not only did life-history traits diverge, with queens becoming highly fecund and long lived compared with their sterile workers, but also individual traits lost their importance compared with colony-level traits. In solitary animals, fecundity is largely influenced by female size, whereas in eusocial insects, colony size and queen number can affect the egg-laying rate. Here, we focused on the ant Temnothorax rugatulus, which exhibits two queen morphs varying in size and reproductive strategy, correlating with their colony's social organization. We experimentally tested the influence of social structure, colony and body size on queen fecundity and investigated links between body size, metabolic rate and survival under paraquat-induced oxidative stress. To gain insight into the molecular physiology underlying the alternative reproductive strategies, we analysed fat body transcriptomes. Per-queen egg production was lower in polygynous colonies when fecundity was limited by worker care. Colony size was a determinant of fecundity rather than body size or queen number, highlighting the super-organismal properties of these societies. The smaller microgynes were more frequently fed by workers and exhibited an increase in metabolic activity, yet they were similarly resistant to oxidative stress. Small queens differentially expressed metabolic genes in the fat body, indicating that shifts in molecular physiology and resource availability allow microgyne queens to compensate for their small size with a more active metabolism without paying increased mortality costs. We provide novel insights into how life-history traits and their associations were modified during social evolution and adapted to queen reproductive strategies.

Reproductive activation in honeybee (Apis mellifera) workers protects against abiotic and biotic stress

Social insect reproductives exhibit exceptional longevity instead of the classic trade-off between somatic maintenance and reproduction. Even normally sterile workers experience a significant increase in life expectancy when they assume a reproductive role. The mechanisms that enable the positive relation between the antagonistic demands of reproduction and somatic maintenance are unclear. To isolate the effect of reproductive activation, honeybee workers were induced to activate their ovaries. These reproductively activated workers were compared to controls for survival and gene expression patterns after exposure to Israeli Acute Paralysis Virus or the oxidative stressor paraquat. Reproductive activation increased survival, indicating better immunity and oxidative stress resistance. After qPCR analysis confirmed our experimental treatments at the physiological level, whole transcriptome analysis revealed that paraquat treatment significantly changed the expression of 1277 genes in the control workers but only two genes in reproductively activated workers, indicating that reproductive activation preemptively protects against oxidative stress. Significant overlap between genes that were upregulated by reproductive activation and in response to paraquat included prominent members of signalling pathways and anti-oxidants known to affect ageing. Thus, while our results confirm a central role of vitellogenin, they also point to other mechanisms to explain the molecular basis of the lack of a cost of reproduction and the exceptional longevity of social insect reproductives. Thus, socially induced reproductive activation preemptively protects honeybee workers against stressors, explaining their longevity. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

Local Variation in Recombination Rates of the Honey Bee (Apis mellifera) Genome among Samples from Six Disparate Populations

Meiotic recombination is an essential component of eukaryotic sexual reproduction but its frequency varies within and between genomes. Although it is well-established that honey bees have a high recombination rate with about 20 cM/Mbp, the proximate and ultimate causes of this exceptional rate are poorly understood. Here, we describe six linkage maps of the Western Honey Bee Apis mellifera that were produced with consistent methodology from samples from distinct parts of the species' near global distribution. We compared the genome-wide rates and distribution of meiotic crossovers among the six maps and found considerable differences. Overall similarity of local recombination rates among our samples was unrelated to geographic or phylogenetic distance of the populations that our samples were derived from. However, the limited sampling constrains the interpretation of our results because it is unclear how representative these samples are. In contrast to previous studies, we found only in two datasets a significant relation between local recombination rate and GC content. Focusing on regions of particularly increased or decreased recombination in specific maps, we identified several enriched gene ontologies in these regions and speculate about their local adaptive relevance. These data are contributing to an increasing comparative effort to gain an understanding of the intra-specific variability of recombination rates and their evolutionary role in honey bees and other social insects.

Recent advances in population and quantitative genomics of honey bees

The increase in the availability of individual Apis mellifera genomes has resulted in significant progress toward understanding the evolution and adaptation of the honey bee. These efforts have identified new subspecies, evolutionary lineages, and a significant number of genes involved with adaptations and colony-level quantitative traits. Many studies have also developed genetic assays that are being used to monitor the movement and admixture of honey bee populations. These resources are valuable for conservation and breeding programs that seek to improve the economic value of colonies or preserve locally adapted populations and subspecies. This review provides a brief discussion on how population and quantitative genomic studies has improved our understanding of the honey bee.