To understand which flowers are important for bees, scientists from the Earlham Institute (EI), with the University of East Anglia (UEA), have developed a new method to rapidly identify the sources of bee pollen.
The rapid pollen analysis uses a method called ‘Reverse Metagenomics’ (RevMet) that can identify the plants that individual bees visit. It uses MinION, a portable DNA sequencer from Oxford Nanopore Technologies.
The portability of the equipment involved means that this type of analysis could be performed on-site where bees are collected and sampled – vastly increasing our understanding of where bees look for pollen on a national scale.
Bees are in vast decline in the UK and across Europe, as are the wildflowers on which they rely. One way to help boost their numbers is by planting the correct wildflowers, providing a better habitat for pollinators to disperse, nest and breed.
However, it is unclear which plant species are the most preferred between different pollinators, including bees, and how this might change over time and in different environmental conditions.
Historically, scientists used light microscopy to identify individual bee-collected pollen grains, which was a time-consuming and impractical method.
Ned Peel, the PhD student who carried out the research in the Leggett Group at EI says: “Importantly, from a mixed sample of pollen, we can also measure the relative quantities of each type of pollen.
“Manual methods to measure pollen and other genomics methods, such as metabarcoding, have been developed – but these can’t accurately measure how much of each different type of pollen is found in a sample.”
Prof Douglas Yu from UEA’s School of Biological Sciences, who had the initial idea for the project, said: “To support our tests, we rapidly generated 49 wild UK plant species. Assembling these genomes would have taken us months of work and required a lot of money.
“With our method, the pollen is separately sequenced with the MinION, which generates long DNA sequences – we then used the 49 reference skims to identify each of the long reads to local plant species.”
“This technique can reliably differentiate species in a mixed sample according to the amount of DNA present of each. The results showed that honeybees, and two species of bumblebee, demonstrate a high preference for one plant species per foraging trip.”
The reverse metagenomics pipeline can be applied to more questions than just what plants bees like to pollinate; we can also understand whether certain wildflowers compete with agricultural flowers for pollinators, or the behaviour of pollinators across large areas and land types.
The method could also be used to study other mixed samples, such as herbivore dung, for diet analysis; and air, to identify airborne allergenic pollen and crop pathogens.
The paper, titled: “Semi-quantitative characterisation of mixed pollen samples using MinION sequencing and Reverse Metagenomics (RevMet)” is published in Methods in Ecology and Evolution