Emory Report
April 14, 2008
Volume 60, Number 27

Amazing ants
• The longest lived ant on record was a queen, who died when she was 25 years old.

• A main defense of ants is to roll over and play dead.

• Leaf-cutting ants carry leaves that are 20 times their body weight to their nests, to feed their fungus gardens.

• Aphids excrete a “honeydew” that is like Gatorade for ants; in return, the ants protect aphids from predators.

• One of the greatest threats to ants is drought.


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April 14, 2008
Following the ant trail

By Carol Clark

Nicole Gerardo was prone on the sidewalk outside the Rollins Research Center when two passersby approached her with concern. “They laughed when I stood up holding a Petri dish,” says Gerardo, who explained that she had just lain down to nab some aphids she noticed crawling on a plant.

“That’s what I do, collect insects,” says Gerardo, assistant professor of biology, who has made field trips to Panama and Ecuador to dig up whole colonies of fungus-growing ants.

Gerardo studies the evolutionary ecology of microbial host-parasite interactions. Aphids and ants happen to be tiny, living laboratories of these interactions.

“Aphids are not just a gardener’s nightmare,” Gerardo says, pointing out that some aphid species are evolutionary marvels, carrying an arsenal against their natural enemies in the form of bacteria. One type of bacteria protects the aphids from a fungal pathogen, while another type combats heat stress and the larvae of a parasitic wasp that lays its eggs on aphids.

“What we’re realizing is not all microbes are bad. Some of them play a key role in the ecology and survival of the organisms around us – and of ourselves,” Gerardo says. Understanding the interactions between a simple system, like that of a bacterium and an insect, might give insights into how more complex systems operate – such as bacteria that promote human health or diseases.

A native of New Mexico, Gerardo joined Emory in January, after completing a postdoctoral fellowship at the Center for Insect Science at the University of Arizona. She moved to Atlanta with her husband, Josh; dog Kylee; and cat Luna. She opens a desk drawer in her lab to reveal a few others who made the trip with her: some Acromyrmex octospinosus fungus-growing ants, including two queens.

“She’s tending her garden,” Gerardo explains, holding up a Petri dish where a large, brown ant fusses over a marble-sized wad of fungus. “They have to weed and feed their fungus, just like a human gardener takes care of plants.”

There are more than 200 species of fungus-growing ants. They range from New Jersey to southern South America, but they especially flourish in the Amazon basin. The ants get nourishment from their fungus, and in turn, they feed the fungus and protect it from predators.

“Ants have been growing fungus for 50 million years,” Gerardo says. “That provides a lot of time for many adaptations to arise, and for the ants’ agricultural practices to become more advanced.”

One example of such an adaptation is bacteria found on the body of some ants that inhibits a killer of the ants’ fungus crop – which happens to be another type of fungus. “Humans go and buy an insecticide for a particular pest in their gardens, but these ants have the pesticide right on their bodies,” Gerardo says.

The fungal pathogen is also interesting, she adds. “It has been specialized to only recognize and attack the ants’ fungus, which makes it a really efficient predator.”

Researchers have documented these basic relationships between the bacteria, the ants and the fungi. Now Gerardo wants to build on these findings by studying the chemical and molecular processes that occur during these interactions. Emory makes an ideal place for this work, due to its opportunities for interdisciplinary research and a strong Population Biology, Ecology and Evolution program, she says.

When she’s not working, Gerardo enjoys training to run in marathons. She is also a founder of the Invertebrate-Parasite Interactions Journal Club, which has members from Emory and Georgia Tech. The researchers hold potlucks where they discuss science articles.

These are dinner parties where the hosts never have to feel embarrassed by a stray insect. Gerardo, for one, says she doesn’t squash the occasional ant that wanders onto her kitchen counter. Instead, she just cleans up the invisible chemical trail it was following and returns the ant to the outdoors — or pops it into a Petri dish.
“I think they’re beautiful,” she says.