Bees play a key role in our ecosystem and in the world's food supply. Thanks to a large collaborative effort, the genomes of two important pollinating bumblebees have been sequenced and compared with those of other bees, laying the foundations for the identification of biological factors essential for their conservation.

Two research articles published in the journal Genome Biology present the first genome sequences and analyses of two key bumblebee species: the European buff-tailed bumblebee, Bombus terrestris, and the North American common eastern bumblebee, Bombus impatiens.

The research focused on identifying similarities and differences between these transatlantic cousins, using bees from Thurgau, Switzerland, and Michigan, USA. The studies also compared them with their more distant relatives, the honeybees, to understand their different social colony lifestyles and how they fight off infections.

Both studies involved large international collaborations and included researchers from the SIB Swiss Institute of Bioinformatics, the University of Geneva Medical School, and ETH Zurich's Institute of Integrative Biology. The projects were coordinated by Dr. Ben Sadd from Illinois State University, Dr. Seth Barribeau from ETH Zurich and East Carolina University, Dr. Kim Worley from the Baylor College of Medicine, and Prof. Paul Schmid-Hempel from ETH Zurich.

Bees: critical but threatened links in the food chain
Bees play an invaluable role in maintaining biodiversity and in pollinating the crops that feed the world. The marked population decline of some species is a serious threat to our agro-ecosystem and it is therefore essential to improve our understanding of their biology and to investigate how they respond to environmental threats. Despite their often slow and apparently bumbling flights from flower to flower, bumblebees are anything but lazy.

With over 250 bumblebee species globally, these important insects perform the laborious task of pollinating flowers in both wild and agricultural settings.

A large number of fruits and vegetables would be missing from our plates had a bumblebee not done its job. "Bumblebees are intriguing creatures to study," explained Dr. Sadd, "but growing threats to their health are affecting bee populations around the world, making it especially critical to improve our understanding of their biology."

Protective immunity and social living
Most bumblebees do not live in isolation, but in colonies of tens to hundreds of related individuals founded each year by a single queen bee after the winter's hibernation. They therefore exhibit a level of social organisation that is intermediate between solitary insects, such as houseflies, and the highly social honeybees, which have colonies of many thousands of individuals with queens that live for several years.

Such social living requires a large degree of cooperation and organisation, especially because dense colonies of many genetically similar individuals make the threat of infections particularly acute.

"The catalogue of genes involved in immune defence responses is well conserved among different bee species regardless of their level of social organisation," explained Dr. Robert Waterhouse from the University of Geneva and the SIB Swiss Institute of Bioinformatics, "but it is much smaller than in solitary insects such as flies and mosquitoes that often live in more pathogen-rich environments."

Nevertheless, variations in evolutionary signatures of selection amongst immune genes from bumblebees and honeybees may point to different pressures exerted by the distinct pathogens that threaten these bees.

Interestingly, exposing young Swiss bumblebees from mature colonies to various bacteria showed generally elevated responses of immune genes in females compared with males. "This," said Dr. Barribeau, "suggests a greater investment in protective immunity by the females, which will one day start their own colonies, than by the males, whose role is essentially just for reproduction."

Research impact
The genomes of these Swiss and American bumblebees provide the first insights into the genetics behind the differences in their behaviours and responses to their environments. "These genomic resources," said Dr. Barribeau, "help us to understand what it is that makes these bumblebees particularly at risk from challenges to their well-being, such as diseases and pesticides."

The sequencing of these bumblebee genomes constitutes a great leap forward for the study of bee biology and the understanding of the organisation of insect societies. The published findings represent many years of work by numerous scientists; but this is only the beginning of a new era of bumblebee research, as these genomes will facilitate many future high-throughput functional studies to advance our knowledge of these engaging and essential insects and thus ensure their conservation.

Sadd BM, et al. The genomes of two key bumblebee species with primitive eusocial organization. Genome Biol 2015.; Barribeau SM, et al. A depauperate immune repertoire precedes evolution of sociality in bees. Genome Biol 2015;16:628.