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The Texas carpenter ant takes “probiotics” to the next level

A spider feeds on a Texas carpenter ant. The ant builds its nests in oak trees in the mountains of West Texas.
Photograph by Joseph Manthey
A spider feeds on a Texas carpenter ant. The ant builds its nests in oak trees in the mountains of West Texas.

The booming probiotics market makes it plain: we humans have come to appreciate our “microbiome.” It's gut-level biology — our digestion relies on the presence of “good bacteria” in our guts.

But one West Texas creature has taken it to another level.

Across millions of years, Texas carpenter ants and Blochmannia bacteria have forged a singular symbiosis. The ant has evolved an organ specifically to host its “good bacteria.” And while we rely on the outside environment to acquire our microbiome, the ants are born with theirs, thanks to the colony's queen. This “mutualistic” bond opens a window into the mysteries of evolution.

Perhaps it's our assumption that the nonhuman world is defined solely by violence and competition, by predator and prey, parasite and host. But “win-win” relationships, which abound in nature, are relatively understudied.

Dr. Joe Manthey is the head of a genomics lab at Texas Tech University. He's exploring the ant-bacteria symbiosis.

“Most of co-evolutionary theory has nothing to do with mutualisms,” Manthey said. “It's very interesting, because it's a totally different set of expectations, when you have positive-positive, versus positive-negative or negative-negative relationships.”

Carpenter ants, genus Camponotus, are found in forests worldwide. They nest in wood, and scavenge the forest floor. It's an omnivorous diet — of dead-insect parts and plant detritus — and it often has nutritional shortcomings.

That's where the Blochmannia come in. The bacteria recycle nitrogen and produce amino acids missing from the ants' diet. The ants can survive without the Blochmannia, but their fitness is markedly compromised.

To study Texas carpenter ants, Manthey came to the Chisos Mountains of Big Bend National Park.

Finding the ants wasn't easy. They nest in oaks, out of reach, and out of sight, and Manthey learned that they forage at night. Eventually, Manthey and his students found two colonies in the Chisos.

“When you see a log,” Manthey said, “and then you see a little pile of sawdust underneath it, from a distance, that's an obvious tell-tale sign that something is burrowing under there. If it's a coarse texture, it's usually the larvae of beetles, and if it's a really fine texture it's usually the carpenter ants. And if you just pull off a little bark, you can usually find them.”

Manthey collected 14 Big Bend ants. He'll sequence the genomes of both the ants and the bacteria. And he's doing the same for carpenter ants and Blochmannia across the American West. Then, he'll compare the findings.

What could that reveal?

A carpenter ant's diet in the Chisos differs from that of an ant in the Hill Country, or the Rocky Mountains. That means that what the Blochmannia does to supplement the ant's diet must also vary.

We can imagine how predator and prey evolve together, in a sort of “arms race.” West Texas pronghorn, for example, evolved their speed to evade the now-vanished American cheetah. But in examining the genes of ants and bacteria, Manthey will see how these two creatures have adapted to survive together, from place to place, in an intricate evolutionary dance.

“We'll be studying at least six species that are widespread,” Manthey said, “and hopefully more, and that will allow us to get at those bigger types of questions of the co-evolution of the ants and their bacteria.”

Carpenter ants and Blochmannia formed their alliance at least 30 million years ago. It's served them well. The poet Alfred Tennyson famously wrote of “nature, red in tooth and claw.” But this pairing reminds us the reality is far stranger.

Drew Stuart is the producer for the Marfa Public Radio series Nature Notes.