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Antspecies' complex cooperation interests scientists
By Becca Evanhoe
bevenhoe@kansan.com
Kansan staff writer
Our story so far: our heroine and her colony of peaceful farming ants stand on the brink of war against a pestilence that threatens their crops and entire way of life. Despite the efforts of her kinsman, a killer fungus has infiltrated her village, laying waste to its farms.
Will her clan survive?
Never fear, now our heroine draws her secret weapon: From her chest, she spaws living bacteria, anly that oozes powerful chemicals. The bacteria spell doom for the evil fungus. In her finest hour, her home-grown biological weapon defeats the invader.
enemy, a bumpy moving surface
And they have won — for now.
Or have they?
The heroine in this story is no comic book character. She's a real, leaf-cutting ant. For the past 40 million years, the leaf-cutters like her have been battling their ancient enemy, a pesky microfungus.
In this comic book scenario, the "evil" fungus, along with the bacteria in the secret weapon and the "good" fungus that the ants farm for food, join the leaf-cutting ants in one of the most complex interspecies relationships known.
species relationship. This microscopic saga has been the subject of Cameron Currie's research for the past eight years. An assistant professor of ecology and evolutionary biology, Currie looks at how these four critters evolved alongside one another for millions of years.
Currie said that much can be learned from these co-evolving groups. "By studying this scenario, we can really shed light on the world of interactions," he said. Laws of this same "world of interactions" governs the relationships between humans and microbes, the battles between health and sickness.
health and science. His latest research may show that the evolutionary script is not a simple two-way contest of "good versus evil."
The main characters
The four characters in this world of interactions live interdependently with each other, a phenomenon called symbiosis. Most of the symbiotic relationships in biology happen between two organisms, but Currie's leaf-cutting ants are the first known four-part symbiosis.
Since the 18th century, scientists knew about fungus-farming ants. Their complex societies and agricultural pursuits are one of the most advanced civilizations in the insect world.
Currie finds his leaf-cutters in the Panama rainforest, where the mounds they call home can measure 20 feet wide by 20 feet long and 10 feet deep in the ground. The leaf-cutting, or attine, ants have been around for 50 million years.
around for 30 million workers in a given colony divide into at least seven different job descriptions based on age and size. For example, forager ants bring leaf fodder into the nests; gardener ants munch on leaves, spit them out, and swab them with fungus. And soldier ants protect the nest from intruders — Currie included.
"The soldier ants can bite through leather shoes," he said. "They bite and bite and bite." Enter the villain
Enter the vienn In addition to the ants' food fungus, Currie discovered a coexisting fungus disease, a pathogen that consumes the leafcutters' gardens. The specialized microfungi occur almost exclusively in fungus gardens.
Currie's early research showed when the gardener ants discover the pathogen, they furiously attempt to rid their gardens of it. For smaller spores, they begin a behavior called "fungus-grooming." The ants detect the pathogen with their antennae and pick up the spores in their mouths and cart the remains off.
But for large, infected patches, the ants begin weeding, a behavior where the ants clear-cut a section of garden, pathogen and all. They team together to unearth big chunks of the fungus patch.
"Ive seen them take an infected patch of a fungus garden and turn it into a crater," Currie said.
The complex world of leaf-cutters seemed to be well-defined amongst the three contenders; the ants, their food fungus, and the pathogen.
An unexpected sidekick
But Currie was also the first to look closely at strange, pale patches that grew on worker ants' bodies, particularly on their chests.
particularly on the
"They had white, cottony stuff
on the plates of their chests. Some
workers were almost all white,
just covered in it," he said. "In the
past, scientists thought it was just a waxy substance.
a waxy substance.
What he found was a fourth player: a special bacteria grew on the ants' own bodies and destroyed the pathogen fungus.
What he came to understand was this: The ants farmed the fungus, which provided their food. In return, the ants kept the fungus well-tended. The "evil" pathogen was using the ants' gardens as easy pickings in a stockpile of food. To ward off this pathogen, the ants employed bacteria that secreted antibiotics to kill the pathogen. The benefit for the bacteria was the ants have special glands on their chests that secrete a form of nutrients for the bacteria.
nurtures for the sex
Currie realized the bacteria weren't just clingers-on. Instead, the team began to question which species was calling the shots; the ants or the microbes?
And the plot thickens
And the plot thickens.
The addition of this fourth player calls into question a host of complicated character motivations and possible symbiotic plots. Little known to our ant heroine, "good versus evil" may no longer apply; this may be a scenario more befitting Machiavelli than Marvel.
There are two possible scenarios, explained Matias Cafaro, a post-doctoral researcher who studies the DNA of the bacteria involved. In the first, the ants evolve as a species, and the other three characters co-evolve alongside. This is the standard theory in biology: the hosts, in this case the ants, lead the show.
But in the second scenario, there is plot twist. What if the microbes evolved first, and the ants were playing catch-up? In this plot, the bacterial ally may not be a tool at the ants' disposal, but in reality may be a character with its own motivations.
with its own model.
If this latter scenario were true,
Cafaro said if the ants are in fact
following the fungus and bacteria
through evolution, then that indicates that the fungus and bacteria are more important partners than we realize.
we realize. "We would have to re-evaluate the role that microbes have in symbiotic systems, and the entire environment," he said. "There's a balance in all symbiotic relationships, but this would change the way we perceive it."
The theory that explains exactly how the microbes may be in charge is called the "Red Queen Hypothesis," named after the Red Queen in Lewis Carroll's Alice in Wonderland, who was running, running and running
just to stay in the same place.
Deborah Smith, assistant professor of ecology and evolutionary biology, said the metaphor describes how the bacteria on the ants and the pathogen are the real combatants, always competing to gain an advantage. If the pathogen develops a resistance to the bacterial antibiotic, then the bacteria must change to become effective again.
effective against Through this arms race, the bacteria and fungus rapidly try to "out-evolve" one another. In this script, the seemingly higher-order ants are really led by their more quickly-evolving microbe cronies — the supposedly lower forms of life.
Currie's most recent research published in the journal Science seemed to indicate that the garden fungus and the pathogen followed the evolutionary whims of the ants. Cafaro will attempt to see if the bacteria have their own agenda by studying the DNA of the bacteria to map its evolution ary course.
But even if the story doesn't
The moral of the story is...
have a dramatic plot twist, Currie, Cafaro, and others agree the details of leaf-cutter society can teach humans much about the underworld of interactions.
the best example of how we can learn from the saga of the leafcutters and their microbial sidekicks is in the arena of antibacterial resistance, said Currie.
"Why have the antibiotics produced by the bacteria been effective against the pathogen for millions of years, when man-made antibiotics have become ineffective in 60 years?" Currie asked.
Craig Martin, professor and chair of the division of ecology and evolutionary biology, agreed that understanding this complex symbiosis motivates scientists to search for similar stories in other places in the environment. But he also believes that the leaf-cutters saga is, in itself, worthwhile.
"I think it illustrates the beauty and complexity that can be obtained by life," said Martin. "To me, that's good enough."
— Edited by Stephanie Lovett