Ant colony 'personalities' shaped by environment

A single 'Temnothorax rugatulus' ant The researchers tracked the ants' behaviour in the wild as well as in the lab

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Ant colonies have their own personalities, which are shaped by the environment, a US study suggests.

Colonies of several hundred ants show consistent differences in the way they behave, just like individual people do.

Certain behaviours go together - for example, a colony that explores more widely for food also tends to respond more aggressively to an intruder.

Such a colony has a more "risk-taking" personality and this was more common in the north, where the climate is colder.

"I'm really interested in why personalities exist," said Sarah Bengston, a PhD student at the University of Arizona who led the research. Her study is published in the journal Proceedings of the Royal Society B.

Ms Bengston explained that although we know most animals have personalities, we do not yet understand why these evolved.

"Sometimes individuals behave differently from one another, and when they do that repeatedly through time, we say that they have a personality."

ant with US penny The rock ants in the study are tiny (pictured with a one cent coin) but show consistent behaviour in colonies

As such, there is nothing to stop a colony of insects from having a personality - as Ms Bengston found when she tracked how colonies behaved up and down the western US, both in the wild and when she bundled them up and watched them in the lab.

Crawling for science

Once back in the lab, whole colonies of 200-600 ants could be filmed inside transparent containers, and the videos analysed to measure things like the level of physical activity and aggressive behaviour. But some measurements, such as how far the ants would go foraging for food, had to be done in the field.

To gather this data, Ms Bengston followed thousands of ants in the great outdoors, mostly in pine and juniper forests. She tagged them with pink fluorescent powder and chased them through the leaf matter on her hands and knees.

"I've done an awful lot of crawling," she told the BBC. "It can get a little tedious but it's also a lot of fun, because you get to see a lot of natural behaviours that we wouldn't necessarily see in the lab.

"I spend a lot of time looking slightly like a crazy person on the side of hiking trails."

Environmental effect

Other research has shown that collective properties, like how much the ants explore, or their aggression levels, can vary from colony to colony. But this is the first study that has measured multiple "dimensions" of personality - and found that some of them group together.

"We found that there was a trade-off in foraging effort, versus nest defence," Ms Bengston said. Both of these behaviours relate to how the colonies handle risk.

"Some colonies are much more happy to take risks in their daily activities, while other colonies are a lot less likely to take risks."

Ant fieldwork To measure how colonies behave, scientists tag individual ants with coloured powder and follow them

Furthermore, there was a shift in these personality traits across the north-south range of the colonies studied, from Washington to Arizona. This suggests that the environment is an important factor in determining a colony's personality.

The study does not reveal exactly what it is about the change in latitude that produces different colony behaviour, but Ms Bengston suspects that the long northern winter plays a role.

"We suspect that it might be related to the time that they have to reproduce," she said.

"In the more northern climates, the snow pack melts pretty late and then they have a very short window in which they need to acquire all of these resources, to reproduce. So they might have to take more risks in order to do that."

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