The Secret Life Of Bees: Texas Researchers Find Gut Bacteria Passed On Through Millennia

AUSTIN, TX — We're not sure how researchers at the University of Texas at Austin know about ancient bees' social lives, but they've made a buzz-worthy claim: About 80 million years ago, a group of bees started exhibiting social behavior — the mundane, yet necessary, stuff of daily living such as raising young together, sharing food resources, defending their colony, and whatnot.

It takes a village, people. In this case, an organized hive. But here's the kicker: Today, descendants of these social-conscious bees from so many millions of years ago — honey bees, sting-less ones and bumblebees — carry "stowaways" from their ancient ancestors: Five species of gut bacteria that have evolved along with the host bees, researchers say.

To recap: These bacteria have been lurking in the guts of subsequent generations of social bees, passed down for 80 million years. This is according to a new study published today in the journal Science Advances and led by researchers at The University of Texas at Austin.

The findings, UT researchers said, advances the idea that social creatures (not only bees but humans) not only transfer bacteria among one another in their own lifetime but have a distinctive relationship with bacteria over time, in some cases even evolving on parallel tracks as species.

“The fact that these bacteria have been with the bees for so long says that they are a key part of the biology of social bees,” says Nancy Moran, a professor of integrative biology at the university who co-led the research with postdoctoral researcher Waldan Kwong. “And it suggests that disrupting the microbiome, through antibiotics or other kinds of stress, could cause health problems.”

Most insects, including non-social bees, don’t have specialized gut microbes, researchers noted. Because they have limited physical contact with individuals of their own species, they tend to get their microbes from their environment. But not social bees, which spend much time in close contact with one another in their hive, making it easy to transfer gut microbes from individual to individual.

“Having a social lifestyle enabled the specialized community of bacteria to diversify along with the bees through deep time,” says Moran.

The last common ancestor of modern social bees picked up five species of bacteria from the environment around 80 million years ago, researchers reiterate. Those bacteria survived and evolved inside the guts of the host bees for millions of years, diversifying into strains that are specific to each new species of social bee that evolved since, scientists add. Those five ancient bacterial lineages still form a major part of the gut microbiota of honey bees and bumble bees, but less so in sting-less bees, which were more likely to lose bacterial lineages over time, according to researchers.

The upshot: Bees may have acquired their core microbiota around the same time as the transition to social lifestyles, researchers have concluded. What's more, researchers noted, closely related bees have more similar microbiomes, suggesting co-diversification of host bees and their microbes.

The co-existence between bee and bacteria yields a symbiotic relationship. Just as these five species of bacteria seem indispensable to their bee hosts, they, too, are unable to exist without their hosts. The bacteria have taken well to their bee living quarters over time: By adapting to life inside bees, they’ve lost their ability to live in the outside world for myriad reasons, chiefly the bee gut's lower oxygen levels than the atmosphere has that make for primo bacteria real estate.

“Most of them can’t live under atmospheric oxygen levels,” Moran explains. “They can’t just grow in nectar or on the surface of a plant. They have to be in the bee gut.”

This is the first study to chart the evolution of the gut community of bacteria in a group of animal hosts so far back in time, according to UT-Austin researchers. Until now, the study that spanned the longest evolution of gut microbiota, led by another UT Austin professor of integrative biology, Howard Ochman, traced three lineages of bacteria living continuously in hominids back about 15 million years.

These findings yield more clues into today's species of bees, of which there are hundreds of species and three main groups. Contemporary honey bees include the domesticated western honey bee, Apis mellifera, which has been spread around the world by humans for honey production and pollination of crops, and some cousins living in Asia and Australia, researchers said. The sting-less variety of bee live in tropical and subtropical regions of the Americas, Southeast Asia, Australia and Africa, researchers add. And the noble bumblebee (prolific pollinators that they are) live mostly in northern temperate climates of the Americas and Eurasia, scientists noted.

Kwong, now a postdoctoral researcher at the University of British Columbia, traveled throughout Asia to collect bees for the project, university officials said. As part of his work, he isolated gut bacteria from 27 bee species (25 social and 2 nonsocial species) and sequenced DNA from the bees’ entire gut microbiomes. For each major species of bacteria, the team built a phylogeny, or evolutionary family tree, that showed how the species branched off into distinct strains.

"And here is the remarkable thing," researchers add with palpable thrill. "If you were to set one of these bacterial family trees—for example, the tree for the variety of Lactobacillus associated with bees—next to the family tree of social bees, they would look strikingly similar. When a new species of bee branches off from its cousins, a new strain of the bacterial species often branches off from its cousins. The end result of this co-speciation is that for the hundreds of species of social bee alive today, each has its own unique strains of shared species of bacteria."

Scientists refer to a species that can’t live on its own without its host—such as these ancient microbes that have specialized to live only in the guts of certain bees—as a symbiont, adds Moran.

“The fact that the phylogeny for the bees mostly matches the phylogeny for the symbiont, that really implies that over time, the main source of the symbionts is other bees," she said. "They’re passing it down within the species. If the microbes were just coming from the environment, you’d expect it to be very mixed up.”

The study’s co-authors also include Luis Medina and Hauke Koch at UT Austin; Kong-Wah Sing at the University of Malaya; Eunice Jia Yu Soh at the National University of Singapore; John Ascher at the National University of Singapore and the American Museum of Natural History; and Rodolfo Jaffé at Vale Institute of Technology and Universidade de São Paulo.

This research was supported by Yale University, Sigma Xi, the Canadian Natural Sciences and Engineering Research Council, the Swiss National Science Foundation, Fundação de Amparo à Pesquisa do Estado de São Paulo, and the U.S. National Science Foundation.

>>> Image provided by University of Texas at Austin