Worker bees can fight infections individually through their immune systems or collectively through social behaviours, such as keeping a clean nest, removing diseased larvae, and grooming themselves and each other.
However, a new study by York University researchers suggests that honey bees have been evolving away from combating pathogens using their individual immune responses.
The study, “Accelerated evolution of innate immunity proteins in social insects: adaptive evolution or relaxed constraint?” published in the journal Molecular Biology and Evolution, shows that most of the honey bee’s innate immune genes are accumulating mutations at a very high rate.
“It seems like the honey bee’s innate immune system is decaying,” says study co-author and York University biology Professor Amro Zayed. “This is a good example of ‘use it or lose it’ in biology.” Mutations in functional genes are quickly removed by natural selection, but in genes that were once useful but are no longer needed, mutations can build up because they are not removed by natural selection. This eventually leads to the “evolutionary decay” of a gene sequence.
“We found that innate immune genes in the honey bee have many more mutations relative to other genes in the bee genome – three to four times more,” says study co-author and York University PhD candidate Brock Harpur.
What is responsible for the decay of innate immune genes in honey bees? “The best explanation is that social honey bees have evolved more effective or less costly mechanisms to deal with pathogens, such as grooming and hygienic behaviour,” says Zayed.
The team’s findings have implications for the conservation of social bees, like honey bees and bumble bees, which may have an increased vulnerability to unfamiliar pathogens.
“Our work suggests that social bees have fewer functional immune genes relative to solitary bees, which possibly increases their susceptibility to new pathogens that are not easily ‘groomed off’,” says Harpur.
He says there is a link between pathogens and the decline of several North American bumble bees, and the research team now plans to study the influence of social behaviour on the evolution of immunity in other solitary and social bee species.