Sequencing of bumblebee genomes will assist conservation

The two endangered species studied are important pollinators of food crops such as nuts, tomatoes, eggplants, peppers, squash and kiwi.

By José Tadeu Arantes

Agência FAPESP – Two bumblebee species that are especially important as pollinators and are endangered on a global scale have had their genomes sequenced. They are the common eastern bumblebee, Bombus impatiens, widespread in North America, and the buff-tailed bumblebee, Bombus terrestris, found in much of Europe.

The first full genome sequences of these two species were obtained by an international consortium coordinated by Ben Sadd, a professor at Illinois State University in the US. The team comprised 144 researchers in 16 countries: Australia, Belgium, Brazil, China, Denmark, Germany, Greece, Ireland, Israel, Japan, New Zealand, Norway, Spain, Switzerland and the United Kingdom, as well as the US. The data were recently published with a comparative analysis of the genomes in the journal Genome Biology. The paper is entitled “The genomes of two key bumblebee species with primitive eusocial organization”.

Brazil has four native species that are phylogenetically close to these North American and European bumblebees: Bombus bellicosus, B. brasiliensis, B. morio and B. pauloensis.

“Bumblebees are important pollinators, helping maintain the biodiversity of natural ecosystems and food crops, such as nuts, tomatoes, eggplants [Solanum melongena], scarlet eggplants [Solanum gilo], bell peppers, squash, kiwi, and many other plants,” said biologist Francis de Morais Franco Nunes, a professor at the Federal University of São Carlos’s Genetics & Evolution Department (DGE-UFSCar) in São Paulo State and the coordinator of the project in Brazil.

In addition to Nunes, the Brazilian team included Daniel Pinheiro from São Paulo State University (UNESP); Fernanda Humann from the São Paulo Federal Institute of Education, Science & Technology (IFSP); and Tiago Falcón, Michelle Soares, Flávia Freitas, Carolina Santos, David Marco Antonio, Klaus Hartfelder, Márcia Bitondi and Zilá Simões from the University of São Paulo.

Pollination by these bees is key to fruit and vegetable crops, with an estimated annual worth of US$170 billion worldwide. Thus, economic as well as environmental concerns contributed strongly to the rationale behind the research.

“Sequencing paves the way for the identification of response mechanisms to risk factors, such as pathogens, insecticides, etc., and genetic elements that can contribute to conservation and breeding,” Nunes told Agência FAPESP.

Like other bee species, bumblebees are social animals. Cooperation and mutual protection partly explain why their evolution has led to the fixation of fewer immune genes than in the genomes of non-social insects such as flies and mosquitoes.

“These two lineages diverged about 18 million years ago. That explains the remarkable similarities in their genetic makeup,” Nunes said.

“The genomes of B. terrestris and B. impatiens have 249 and 248 megabases, respectively, which is very close to the 250 Mb genome of the European honeybee, Apis mellifera, the bee species about which the most research has been done to date.” A megabase (Mb) is a million base pairs. Base pairs, which form between specific nucleic acids, are the building blocks of the DNA double helix.

The genomes of bumblebees and honeybees are identical in several gene categories, such as genes relating to development from embryo to adult, genes for organization and social behavior, and detoxification-related genes.

On the other hand, some genes are specific to bumblebees, such as those relating to muscle function. “That has to do with the bumblebee’s particular pollinating behavior,” Nunes said. “On approaching flowers, it can vigorously vibrate its thorax to shake off the grains of pollen stored in their anthers. This vibratory behavior doesn’t occur in honeybees.”

Different recipes

Another very frequent group of genes in bumblebees relate to gustation (taste), possibly because their nesting habits involve the use of different materials.

“Although the main olfactory genes are present in bumblebees, the study indicated greater sensitivity to taste than smell. The opposite is the case with honeybees, whose olfactory genes are more abundant than those relating to taste. Genome sequencing has therefore corroborated observations of ecological and behavioral differences between the two genera,” Nunes said.

The Brazilian researchers’ contributions to the international consortium focused on analyzing gene content relating to developmental pathways in molting, metamorphosis and exoskeleton dynamics.

“We found that this gene repertoire shows striking similarities among different types of bees, both solitary and social. The differences observed in their morphologies, physiologies and lifestyles aren’t explained by gene content but by the regulatory and functional dynamics of these genomes,” Nunes said.

“The ingredients [genes] are the same, but the recipes [regulation of gene activity in response to genetic and environmental factors] are different.”