Looking at ants to find answers about aggression

Researchers develop model for how collective intelligence works in ant colonies

January 23, 2017

Pavement ants
Three pavement ants touch antennae to determine if they are nestmates. Photo courtesy Michael Greene.

Ants are pretty smart—smart enough that humans study their collective intelligence to draw lessons about how to respond to traffic jams, create efficient computer networks and understand how social media might turn peaceful protesters into a violent mob.

But an individual ant, that’s a different story.

Andrew Bubak (left) and Michael Greene
Graduate school student Andrew Bubak, left, and Professor Michael Greene

“An ant is kind of dumb, honestly. It’s good at its job, it assesses information around it, it brings food home sometimes, but if you watch an individual ant, you’ll wonder why ants ever made it,” said Michael Greene, PhD, a professor in the University of Colorado Denver’s Department of Integrative Biology.

The collective intelligence of ants living in huge colonies is one of the reasons they made it, and it’s all the more impressive because ants don’t give or take orders from each other—despite having queens, ants aren’t hierarchical, and colonies don’t have a central authority. Crucial decisions like when to go to battle with nearby rival colonies come down to the decisions and actions of individual ants. Yet within minutes, information will spread within colonies, and tens of thousands of ants can take action.

“It’s remarkable in its complexity and almost hard to believe sometimes,” Greene said.

The process, also called swarm intelligence, has impressed entomologists, computer scientists and even Southwest Airlines, which uses algorithms derived from ants to try to find more efficient ways to put passengers on planes. It could even inspire lessons about violence.

So far, scientists haven’t unlocked what’s going on in ants’ brains, but University of Colorado Denver | Anschutz Medical Campus researchers think they’ve taken a big step forward. They published their findings in November in the peer-reviewed online journal PLOS One.

Understanding intelligence

Pavement ant swarm
Swarms of pavement ants. Ants from different colonies can engage in fights involving thousands of ants.

Greene is careful when describing ant intelligence. It’s not human cognition, he said. Individual ants respond to environmental cues they pick up through senses such as touch and smell. Actions are based on behavioral rules encoded in ants’ nervous systems.

“I would say they’re thinking in a physiological way, but they’re not conscious,” Greene said.

Ants spread information to each other through chemical cues they share by using their antennae.

“While we know much about the sensory information used and the behaviors displayed, we know far less about the neurophysiological mechanisms that regulate these decisions,” Greene said. The researchers on this paper wanted to find the causal mechanisms behind those decisions.

To do that, they plucked worker pavement ants (Tetramorium caespitum) from the CU Denver campus. Back in the lab, they measured how levels of three neurotransmitters changed when the ants were alone, interacted with nestmates or encountered ants from different nests.

They were trying to determine what happened when the ants fought.

Pavement ants are a species that flourish in cities, with rival nests crowded next to each other. Their food supply depends on them protecting and expanding their territory, so battles are vital to a colonies’ success.

But fighting takes up a lot of resources. Fights between pavement ants are rarely lethal—Greene compares them to dance offs—but they last for 12 to 14 hours and engage whole colonies. That’s a lot of time to be dancing.

“It’s time that would have been better spent foraging,” said Andrew Bubak, a graduate student in CU Anschutz neuroscience program and the CU Denver integrative biology department. He was the paper’s lead author.

Pavement ants
Three pavement ants touch antennae to determine if they are nestmates. Photo courtesy Michael Greene.

The team found a major factor in whether an ant decided to fight was how recently it interacted with other ants from its nest. The researchers found that the neurotransmitters serotonin and octopamine, which is the invertebrate equivalent of norepinephrine, increase when ants are with nestmates. To see whether manipulating those neurotransmitters in solitary ants could mimic a social interaction with a nestmate, the team pharmacologically raised serotonin and octopamine in isolated ants and placed them in an arena with a similarly treated non-nestmate. The ants were fooled, and when they found a rival, they were more likely to fight.

What ants can teach us about violence

For scientists studying ants, the big takeaway is an understanding of the connection of neurophysiological mechanisms to the behavioral outcome of aggression and war, Greene said.

It’s possible to broadly draw a few lessons for humans, Greene said.

“Ants are not people, but one thing we know is that humans do have some antlike behavior,” he said. The most fearsome example might be how people act in large crowds.

“At the broadest level, understanding how pavement ants collectively-organize into fights with neighbors should help us understand how humans also collectively-organize into violence including riots and revolutions,” Greene said.

Greene likened social media to the environmental cues an ant might receive, using the example of how Twitter and Facebook posts affected civil unrest in the Middle East over the past decade. Each person in the crowd can respond to the cue, deciding either to remain peaceful or move to violence. A series of thousands of individual responses suddenly becomes a collective decision.

He said the study also broadens the understanding of the role neurotransmitters play in the decision to be aggressive and how sensory input affects decisions.

In addition to Greene and Bubak, CU Denver integrative biology professor John Swallow, PhD, was another coauthor, along with two researchers from the University of South Dakota.