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Tracking Study Discovers Ants Change Careers As They Age

April 22, 2013
Image Caption: Computer tracking of tagged ants demonstrated that workers divided into three specialized groups — but often switched groups as they aged. Credit: Alessandro Crespi / University of Lausanne

Lawrence LeBlond for redOrbit.com – Your Universe Online

A single ant colony can have thousands of ants, all scurrying around performing various tasks, maintaining their territory for the queen. And because they all look alike, studying them individually by eye can prove extremely difficult, if not impossible.

To bypass this obstacle, Danielle Mersch and colleagues from the University of Lausanne tagged every single worker in entire ant colonies and tracked them by computer. The research, which was conducted entirely in the lab with indoor ant colonies, produced the largest-ever data set on ant interactions.

“It was a very challenging task to tag all the ants,” added Professor Laurent Keller, Director of Ecology and Evolution at Lausanne, according to Mail Online´s Rachel Reilly.

Each ant in six separate colonies of 100 ants each was tagged with a special barcode symbol that allowed a computer to monitor every single move, snapping images twice per second over a 41-day period. The ant colonies were flat enclosures that were monitored by overhead cameras. Over the course of the study, the researchers collected more than 2.4 billion readings and 9.4 million interactions between the worker ants.

The biologists, publishing the research in the journal Science, discovered that the ants (Camponotus fellah) fell into three distinct social groups that perform different roles for the colony: nursing the queen and the young; cleaning the colony; and foraging for food. Ants in each group move around a specific part of the nest, but do graduate from one group to another as they age.

“The paper is a game-changer, in the size and detail of the data set that was collected,” Anna Dornhaus, an entomologist at the University of Arizona in Tucson, said in a statement. “Different methods of automatically tracking animal behavior have recently been developed, and this is one of the first empirical studies that have come out as a result.”

As for the ant groups, the researchers discovered that, on average, the colonies were made up of 40 percent nurses, which stayed within the vicinity of the queen and her brood in the inner nest; 30 percent were cleaners, who were found throughout the rest of the nest, and were the only ones likely to visit rubbish heaps; the other 30 percent were foragers and were the ones most likely to be found outside the nest and near the entrance.

The team found that the nurses tended to be the youngest of the worker ants in the colony, with the next age group being cleaners and the elders being foragers. However, Mersch noted that these career changes were not clear-cut. “You can find very old nurses and very young foragers.”

Mersch noted that heat maps that represented the workers´ positions confirmed that nurses and foragers largely stick to their own company and rarely mingle with each other, even when the brood chamber is near the entrance to the nest. Cleaners are more widely dispersed, interacting with both groups, as they patrol the colony cleaning and bringing food from the foragers to the brood.

The organizational skills of these colonies likely have far-reaching effects, according to the study authors. Foragers were able to communicate efficiently to others within their group where food locations were without bothering the entire colony. And by sticking together, they could keep parasites or disease between themselves without endangering the queen and her brood.

The next step for Mersch and her team is to understand why the ants move from one job to another. “With all the data we have on activity and spatial structure, can we actually determine which ants will do which tasks in the future, based on their current state?” speculated Mersch.

Mersch and colleagues´ study provides the clearest evidence yet that ants go through the same transitions from young nurses to old foragers as has been found with honeybees.

“Like bees, we have now shown that ants´ behavior [also] changes with age,” Prof. Keller added.


Source: Lawrence LeBlond for redOrbit.com - Your Universe Online