Social bees have surprisingly strong body armor against microbes, researchers have found. And the more gregarious the bees--the larger their colonies and the more closely related--the better they are at beating disease. The discovery is the first clear link between the evolution of immune systems and social behavior, and it dangles a new hope for bioprospectors on the trail of the next generation of antibiotics.
Insects, like humans, face greater risks of catching and spreading infectious diseases when they're crowded together. Scientists have long suspected that bees and other bugs combat the added risk that being social incurs by evolving stronger disease defenses, such as secreting antimicrobial agents to cover their bodies. The theory is that bigger colonies with more crowded conditions would require insects to evolve better immune defenses, which in turn enable the insects to evolve still-bigger colonies.
To test the idea, biologists Adam Stow, Andrew Beattie, and their colleagues at Macquarie University in New South Wales and the South Australian Museum in Adelaide collected bees from across the social spectrum: blue-banded bees and teddy bear bees, which are solitary and live in their own nests without partners or workers; semisocial reed bees that partner with their sisters and their offspring in small colonies; and Australian native honey bees, which form large colonies of closely related individuals with sophisticated divisions of labor. The scientists then washed the protective coatings from the bees' bodies and applied the resulting solution to the notorious Staphylococcus aureus (staph) bacterium.
By measuring how much of each solution it took to stop the staph's growth, the researchers determined the strength of each kind of bee's body coating. All the coatings killed bacteria, but the social bees' antimicrobials proved much more powerful than expected, says Stow. Antimicrobial armor from the most social bees was 314 times stronger than that from the most solitary bees, the team reports online this week in Biology Letters, and even the most mildly social bees were 10 times more protected than their solitary counterparts.
The mysterious bacteria-busting secretions of bees and other insects could someday offer an alternative to today's antibiotics, says Stow. "If you're going to look in nature for antibiotics," he says, "this tells you where to look."
For Oxford ecologist Robert May, the finding is crucial and long overdue. "While the idea isn't new, the demonstration is clear, elegant, and the first,” he says. "It's just very nice."