Thanks to olfactory receptors, certain food smells can make the mouth water. The small membrane proteins in the nose send signals to your brain about smell. But in bees, smell is not just associated with food or finding flowers but is also an important factor for survival and communication with mating partners (nest-mates).
To get a better understanding of these scent cues, scientists from the National Centre for Biological Sciences (NCBS), Bengaluru found solitary bees have over 100 olfactory receptors to help them perceive different smells. The results were recently published in Scientific Reports .
Odour signature
Solitary bees are different from honey bees. Most of the bee population are solitary and these wild bees are responsible for pollination of up to 80% of flowering plants. Tomatoes, brinjal, blueberries and cranberries are mostly pollinated by these solitary bees. With almost 40% of the human kept honey bees dying each year scientists have started studying solitary bees as a positive alternative.
“It is important to identify and study the olfactory receptors as bees mainly depend on scent cues. They have an excellent memory and can identify and remember the smell of their preferred food plants. Social bees, like honey bees use many different odours (pheromones) to communicate among each other. There are about 10-12 different pheromones with different messages,” explains Dr. Axel Brockmann, scientist at NCBS and one of the authors of the paper.
For example, scents like cuticular hydrocarbons help identify members of the same nest whereas the queen mandibular gland pheromones are important for the social integrity of the colony. “Bees are capable of producing alarm pheromones. When the nest is under some threat, the workers produce a scent to warn or recruit nest-mates for a defence,” he adds.
Computational analysis
The scientists identified the olfactory receptors by using a new bioinformatics pipeline to compare social and solitary bees. “We found over 40 new olfactory receptors from each of the sequenced genomes in the two solitary bees. The previous annotation on solitary bees missed a whole chunk of data regarding their olfactory genes,” explains Snehal D Karpe, research scholar at NCBS and first author of the paper.
The solitary bee Dufourea novaeangliae has 112 olfactory receptors, while Habropoda laboriosa , another solitary bee, has a high number of 151. Previous analysis has shown that the social honey bees possess approximately 180 olfactory receptors. They examined if there is a higher demand for olfactory receptors in social bees and found that there is no consistent increase in number of olfactory receptors from solitary bees to social bees.i
In addition, they found a group of candidate olfactory receptors responding to queen mandibular gland pheromones which was expanded in honey bees, but not in solitary bees. This may be due to the fact that solitary bees do not have a queen. Also the putative floral scent receptors were found to be enriched in honey bees visiting multiple kinds of flowers than the specialist solitary bees which visit only one kind of flowers.
“Due to the large range of olfactory receptors, detailed functional characterisation of genes remains difficult. Such a bioinformatics overview and comparison provide excellent opportunities to observe interesting differences amongst honeybees and solitary bees. Such comparisons could have implications in our understanding of aberrations in human social behaviour too.” says R. Sowdhamini, scientist at NCBS and corresponding author of the paper.
