Nov. 25, 2008 Ants specializing on one job such as snatching food from a picnic are no more efficient than "Jane-of-all-trade" ants, according to new research.
The finding casts doubt on the idea that the world-wide success of ants stems from job specialization within the colony. Ants are found on every continent besides Antarctica.
"The question is, why is job specialization a good thing?" said Anna Dornhaus of The University of Arizona in Tucson. "We thought that the fact that ants have specialists was one of the things that made them so successful and live all over the world in all habitats in great numbers.
"It turns out that the ones that are specialized on a particular job are not particularly good at doing that job."
Dornhaus studied the rock ant, known by scientists as Temnothorax albipennis, that lives in cracks in rocks in Europe. In ant colonies, all the workers are females.
She videotaped individual ants as they performed four typical ant tasks: brood transport, collecting sweets, foraging for animal protein and nest building. The videotape allowed her to compare how long it took each ant to do a particular task.
Dornhaus, a UA assistant professor of ecology and evolutionary biology, is publishing her paper, "Specialization Does Not Predict Individual Efficiency in an Ant," in the Nov. 18 issue of the online journal PLoS Biology. The German Science Foundation (DFG) funded some of the research.
Adam Smith, the father of modern economics, wrote in 1776 that specialized labor provided benefits to human industry.
Dornhaus, who studies social insects, wanted to see if this applied to ants because efficiency in ants had rarely been tested.
The workers of rock ants, like those of most ant species, all look the same and do not appear physically specialized for any particular task. Nevertheless, they do specialize.
She expected rock ants that specialized would work more efficiently, but that's not what she found.
To identify the individual workers, which are half the size of a grain of rice, Dornhaus color-coded them with model airplane paint in colors such as rally green and racing red using hair-thin wires as paintbrushes.
She crafted nests for the ants by sandwiching cardboard squares between two glass slides. A tiny tunnel in the cardboard let the ants leave the nest.
Dornhaus tested 1,142 workers from 11 colonies that ranged in size from 27 to 233 workers.
To watch ants in action, Dornhaus put individual colonies in a square arena that was 22 centimeters (about eight-and-half inches) on a side and recorded workers' job performance with two video cameras.
For example, in the brood transport test, she placed a colony and an empty nest 10 centimeters (4 inches) apart. Then she took the roof off the colony's nest by taking off the top slide. Once their nest was destroyed, Dornhaus recorded how long the ants took to find the empty nest and move the eggs and larvae to it.
She measured how often and how readily an individual ant performed each task and considered an ant more specialized the more it concentrated its work on one task.
Dornhaus said some go-getter ants eagerly worked in all of the tasks, but other ants seemed lazy. Although the specialists were not more efficient, they put in more hours of work.
It's not known why ants choose the jobs they do, or why some are slow to begin work.
She said it might be explained by how quickly an individual detects work to be done, like noticing dirty dishes in the sink.
A person with a lower threshold will notice and wash the dishes as soon as there are one or two in the sink. However, a person with a higher threshold doesn't notice the dishes until there are at least 10 piled up. The dishes will still be washed, just not as frequently.
"You get division of labor that way just because they have differences in their sensory systems or somehow in the way they interpret the world without consciously wanting to divide labor," Dornhaus said.
The ability to sense work also varies in ants, she suspects.
Dornhaus found that specialists and generalists work equally fast, but the question of employee of the month is still unanswered.
Even though putting in longer hours might seem like the way to success, it wastes colony resources.
"Speed does matter because every minute they spend outside is dangerous and energy costly," she said. "They burn fuel, and they risk dying."
Her next step is investigating "switching costs," such as the time it takes to walk from one side of the nest to the other or the break in concentration when switching between tasks. Dornhaus suggests specialization might minimize such costs.
"I do science because I think it's cool to find out how the world works, specifically how social insects works," Dornhaus said. "Isn't it cool to know that there are little societies underground everywhere you walk?"
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- Dornhaus et al. Specialization Does Not Predict Individual Efficiency in an Ant. PLoS Biology, 2008; 6 (11): e285 DOI: 10.1371/journal.pbio.0060285
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