When working ants take a sick day, the whole colony benefits

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Scientists have shown that the social insect Lasius niger (or black garden ant) changes its behavior following exposure to a fungus, a strategy that protects the most vulnerable and important members of the colony from infection. Their findings, which have been difficult for researchers to measure tangibly, provide the first evidence that animal social networks can adapt to decrease the spread of disease. Here, Nathalie Stroeymeyt and colleagues tested whether colonies change their patterns of social contact in response to the threat of infection by developing an automated tracking system that zeroed in on 22 colonies for 24 hours. They closely studied the movement of both individual ants exposed to Metarhizium brunneum spores and of their unexposed nestmates, comparing social network activities before and after introduction of the spores. Interestingly, not only did infected workers alter their behavior after exposure, but healthy workers altered their behavior toward their infected counterparts, the authors found. They observed that both exposed and unexposed workers maintained their distance from indoor workers by active isolation – increasing their time outside away from the nest. Indoor workers, too, increased their movement to avoid further interaction with colony members. Stroeymeyt et al. saw that such responses kept fungal infection at bay. The responses among the ants were potentially triggered by chemical or mechanical cues associated with Metarhizium brunneum spores, they say, though additional research is needed to better grasp the underlying detection processes involved. The ants' ability to adopt a flexible social network on demand may represent a widespread tactic to survive environmental hazards, according to the authors, minimizing risk to high-value colony members including the queen and young workers.

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http://dx.doi.org/10.1126/science.aat4793

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