Adam Smith, the father of modern economics, wrote in 1776 that specialized labor provides benefits to human industry, and similar benefits have been suggested to explain the world-wide success of ants, and other social insects which live in colonies. Ants are found on every continent besides Antarctica, and their success has been attributed to the evolution of specialization - it has been theorized that this increases the efficiency of individual workers - but has rarely been measured. However, a new paper by Anna Dornhaus, published in this week's issue of PLoS Biology, shows that individual rock ants (Temnothorax albipennis) specializing on one task are no more efficient than those that perform multiple tasks.
Rock ants are not physically specialized for any particular task. Dornhaus, of The University of Arizona, measured how often and how readily individual ants performed certain tasks and considered an ant more specialized the more it concentrated its work on one particular task. She expected rock ants that specialized to work more efficiently, but that's not what she found. Dornhaus explains, "It turns out that the ones that are specialized on a particular job are not particularly good at doing that job."
To identify individual ants, which are half the size of a grain of rice, Dornhaus color-coded them with model airplane paints such as rally green and racing red by using hair-thin wires as paintbrushes. A total of 1142 ants from 11 colonies were individually marked and then filmed performing four typical ant tasks: brood transport, collecting sweets, foraging for protein, and nest building.
Although the specialists were not more efficient, they did put in more hours of work. Even though putting in longer hours might seem like the way to success, it wastes colony resources. Dornhaus found that specialists and generalists work equally fast. "Speed does matter because every minute they spend outside is dangerous and energy costly," she said. "They burn fuel, and they risk dying."
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.
Dornhaus concludes that, at least in this species, a task is not primarily performed by individuals that are especially adapted to it. How much these results apply to the other tasks performed by these ants, or other ant species, or even social insects more generally, remains to be verified. Dorrnhaus's 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.
Citation: Dornhaus A (2008) Specialization does not predict individual efficiency in an ant. PLoS Biol 6(11): e285. doi:10.1371/journal.pbio.0060285
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University of Arizona
Department of Ecology and Evolutionary Biology
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Mari N. Jensen