BackgroundThe shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats.ResultsWe report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits.ConclusionsThese two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0623-3) contains supplementary material, which is available to authorized users.

BackgroundSociality has many rewards, but can also be dangerous, as high population density and low genetic diversity, common in social insects, is ideal for parasite transmission. Despite this risk, honeybees and other sequenced social insects have far fewer canonical immune genes relative to solitary insects. Social protection from infection, including behavioral responses, may explain this depauperate immune repertoire. Here, based on full genome sequences, we describe the immune repertoire of two ecologically and commercially important bumblebee species that diverged approximately 18 million years ago, the North American Bombus impatiens and European Bombus terrestris.ResultsWe find that the immune systems of these bumblebees, two species of honeybee, and a solitary leafcutting bee, are strikingly similar. Transcriptional assays confirm the expression of many of these genes in an immunological context and more strongly in young queens than males, affirming Bateman’s principle of greater investment in female immunity. We find evidence of positive selection in genes encoding antiviral responses, components of the Toll and JAK/STAT pathways, and serine protease inhibitors in both social and solitary bees. Finally, we detect many genes across pathways that differ in selection between bumblebees and honeybees, or between the social and solitary clades.ConclusionsThe similarity in immune complement across a gradient of sociality suggests that a reduced immune repertoire predates the evolution of sociality in bees. The differences in selection on immune genes likely reflect divergent pressures exerted by parasites across social contexts.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0628-y) contains supplementary material, which is available to authorized users.

In many systems, the number of prey killed by predators increases with prey density. Th is in turn generates higher levels of the indirect signals that prey use to assess predation risk. A model developed by Peacor (2003) showed that prey that respond to predator cues without accounting for conspecifi c density will consistently over-or under-estimate risk and therefore invest improperly in anti-predator defense. We tested this model using Rana temporaria tadpoles as prey and Aeshna cyanea dragonfl y larvae as predators. As assumed by the model, prey reduced risky activity with increasing concentrations of predator kairomones and increased activity at high prey density. However, prey did not react to changes in cue or density if the ratio of cue-to-density remained constant. Prey therefore monitored their per capita risk, strongly supporting Peacor ' s model.

ResearchCite this article: Näpflin K, Schmid-Hempel P. 2016 Immune response and gut microbial community structure in bumblebees after microbiota transplants. Proc. R. Soc. B 283: 20160312. http://dx

To what extent host-associated microbiota assembly is driven by host selection or simply by happenstance remains an open question in microbiome research. Here, we take a first step towards elucidating the relative importance of host selection on the establishing gut microbial community in an ecologically relevant organism. We presented germ-free bumblebee, Bombus terrestris, workers from 10 colonies with a "global" microbial species pool comprised of an equal mixture of the gut microbiota of all colonies. By means of 16S amplicon sequencing, we found that overall microbiota community composition was generally shifted between pool-exposed workers compared to workers that naturally acquired their gut microbiota, but that the specific composition of the established microbiota also depended on colony identity (e.g. genetic background). Because the microbiota is protective against parasite infection in this system, variation in the filtering of a beneficial microbial community can have important consequences for host resistance and eventual co-evolution with parasites.