If you happened to be paying attention on the lowland savannahs of Kenya, you might sight small, golden East African honeybees. Take a trip up into the mountain forests, however, and you’d see that the bees there are much darker and larger. Apart from their physical appearance, the mountain-dwelling bees are less aggressive, can fly at lower temperatures than the lowland bees, and are also able to conserve honey when flowers aren’t blooming. These adaptations to high-altitude life led researchers to previously assume that the mountain bees were a distinct subspecies.
However, in a new study, Martin Hasselmann and colleagues sequenced the genomes of 39 bees from lowland and highland populations and found a high degree of similarity in their genomes. This suggests that rather than being distinct subspecies, the bees in fact interbreed constantly.
The researchers also found that two regions located on chromosomes 7 and 9 showed consistent differences between the bee populations, indicating that the genetic variation may have arisen a long time ago. The variations probably existed in bee populations even before they spread into the mountain and savannah habitats, which then exerted selective pressures. These variations likely arose from structural rearrangements of the chromosome segments, which suppress DNA exchange. This preserves genetic differences even when populations interbreed.
The segment on chromosome 7 includes receptor genes for a neurotransmitter called octopamine, which plays a role in learning and foraging and has previously been identified as an important signal in insects living in low temperature conditions. Gene variants may therefore help facilitate the mountain-dwelling bees’ high-altitude lifestyle.
This comprehensive study of the genomes of Kenyan honeybees reveals new insights into their evolutionary history and the genetic basis of local adaptation. Hasselmann adds:
“Our findings complement several other landmark studies (for example in Heliconius butterflies and Solenopsis ants) where adaptations have been similarly tied to structural variants or supergenes. However, this phenomenon has never been documented in honeybees before. Our results should therefore spur further research into the role of supergenes in environmental adaptation. We are planning now to measure the distribution of these divergent segments in other geographic locations and to elucidate the functional link of these genes with behavior.”
Research Article: Wallberg A, Schöning C, Webster MT, Hasselmann M (2017) Two extended haplotype blocks are associated with adaptation to high altitude habitats in East African honey bees. PLoS Genet 13(5): e1006792. https://doi.org/10.1371/journal.pgen.1006792
Image Credit: Andreas Wallberg and colleagues.