About 80 million years ago (Cretaceous period), a group of bees began exhibiting social behavior. Today, their descendants — honey bees, stingless bees, and bumble bees — carry ‘stowaways’ from their ancient ancestors.
The stingless bee Trigonisca ameliae in Colombian copal. Image credit: Dr David Penney / University of Manchester.
At least five host-specific species of bacteria, living symbiotically in the guts of social bees, have been passed from generation to generation for 80 million years, according to a study published in the March 29, 2017 issue of the journal Science Advances.
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.
“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,” said lead co-author Nancy Moran, a professor of integrative biology at the University of Texas, Austin.
“And it suggests that disrupting the microbiome, through antibiotics or other kinds of stress, could cause health problems.”
Most insects, including nonsocial bees, don’t have specialized gut microbes. Because they have limited physical contact with individuals of their own species, they tend to get their microbes from their environment.
Social bees, on the other hand, spend much time in close contact with one another in the 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,” Prof. Moran said.
The last common ancestor of modern social bees picked up five species of bacteria from the environment around 80 million years ago.
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 then.
Those five ancient bacterial lineages still form a major part of the gut microbiota of honey bees and bumble bees, but less so in stingless bees, which were more likely to lose bacterial lineages over time.
Just as these five species of bacteria seem to be indispensable to their bee hosts, they too can’t live without their hosts.
By adapting to life inside bees, they’ve lost their ability to live in the outside world. For example, the bee gut has lower oxygen levels than the atmosphere has.
“Most of them can’t live under atmospheric oxygen levels. They can’t just grow in nectar or on the surface of a plant. They have to be in the bee gut,” Prof. Moran said.
According to entomologists, there are hundreds of species and three main groups of social bees living today.
The 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.
Stingless bees live in tropical and subtropical regions of the Americas, Southeast Asia, Australia and Africa.
Bumble bees live mostly in northern temperate climates of the Americas and Eurasia.
For the study, the researchers 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 authors built a phylogeny, or evolutionary family tree, that showed how the species branched off into distinct strains.
And here is the remarkable thing: 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.
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Waldan K. Kwong et al. 2017. Dynamic microbiome evolution in social bees. Science Advances 3 (3): e1600513; doi: 10.1126/sciadv.1600513
This article is based on text provided by the University of Texas at Austin.
