The genomes of two key bumblebee species with primitive eusocial organization

Background: The 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. Results: We 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. Conclusions: These 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

A depauperate immune repertoire precedes evolution of sociality in bees

Background Sociality 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. Results We 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. Conclusions The 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

Host effects on microbiota community assembly

ISSN:0021-8790ISSN:1365-265

OTU Centroid Sequences

Reference sequence for each OTU

Data from: Host effects on microbiota community assembly

1. To what extent host-associated microbiota assembly is driven by host selection or simply by happenstance remains an open question in microbiome research. 2. 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. 3. We presented germ-free bumblebee, Bombus terrestris, workers from ten colonies with a “global” microbial species pool comprised of an equal mixture of the gut microbiota of all colonies. 4. By means of 16S amplicon sequencing, we found that while 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). 5. 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

Data from: High gut microbiota diversity provides lower resistance against infection by an intestinal parasite in bumblebees

The microbiome, especially the gut flora, is known to affect the interaction between parasites and their hosts. In this context, a parasitic infection can be viewed as an invasion into the pre-existing microbial ecological community. Hence, in addition to the intrinsic defense mechanisms of the host itself, infection success depends on the colonization resistance of the microbiota. In the bumblebee, Bombus terrestris, the microbiota provides resistance to the intestinal parasite, Crithidia bombi, yet which properties actually provide protection remains largely unknown. Here, we show that the community structure of the gut microbiota - in terms of bacterial operational taxonomic units (OTUs) of 16S rRNA gene sequences - prior to parasite exposure can be informative of the eventual infection outcome. Specifically, higher microbiota OTU diversity and evenness are associated with less resistance. However, the microbial community structure does not differ between infected and non-infected individuals, or between infected individuals of varying susceptibility. This suggests that parasite infection success depends on microbiota composition but subsequent changes occur, although the exact alteration that occur remain elusive. In fact, the bumblebee microbiota is surprisingly unaffected by parasite exposure and infection. Rather, the microbiota-host interactions prior to parasite exposure seems a key mechanism regulating resistance to infection

High Gut Microbiota Diversity Provides Lower Resistance against Infection by an Intestinal Parasite in Bumblebees

ISSN:0003-0147ISSN:1537-532

Sample Metadata

Sample informatio

Data from: Immune response and gut microbial community structure in bumblebees after microbiota transplants

Microbial communities are a key component of host health. As the microbiota is initially ‘foreign’ to a host, the host's immune system should respond to its acquisition. Such variation in the response should relate not only to host genetic background, but also to differences in the beneficial properties of the microbiota. However, little is known about such interactions. Here, we investigate the gut microbiota of the bumblebee, Bombus terrestris, which has a protective function against the bee's natural trypanosome gut parasite, Crithidia bombi. We transplanted ‘resistant’ and ‘susceptible’ microbiota into ‘resistant’ and ‘susceptible’ host backgrounds, and studied the activity of the host immune system. We found that bees from different resistance backgrounds receiving a microbiota differed in aspects of their immune response. At the same time, the elicited immune response also depended on the received microbiota's resistance phenotype. Furthermore, the microbial community composition differed between microbiota resistance phenotypes (resistant versus susceptible). Our results underline the complex feedback between the host's ability to potentially exert selection on the establishment of a microbial community and the influence of the microbial community on the host immune response in turn