Ant colonies prefer infected over uninfected nest sites.
During colony relocation, the selection of a new nest involves exploration and assessment of potential sites followed by colony movement on the basis of a collective decision making process. Hygiene and pathogen load of the potential nest sites are factors worker scouts might evaluate, given the high risk of epidemics in group-living animals. Choosing nest sites free of pathogens is hypothesized to be highly efficient in invasive ants as each of their introduced populations is often an open network of nests exchanging individuals (unicolonial) with frequent relocation into new nest sites and low genetic diversity, likely making these species particularly vulnerable to parasites and diseases. We investigated the nest site preference of the invasive pharaoh ant, Monomorium pharaonis, through binary choice tests between three nest types: nests containing dead nestmates overgrown with sporulating mycelium of the entomopathogenic fungus Metarhizium brunneum (infected nests), nests containing nestmates killed by freezing (uninfected nests), and empty nests. In contrast to the expectation pharaoh ant colonies preferentially (84%) moved into the infected nest when presented with the choice of an infected and an uninfected nest. The ants had an intermediate preference for empty nests. Pharaoh ants display an overall preference for infected nests during colony relocation. While we cannot rule out that the ants are actually manipulated by the pathogen, we propose that this preference might be an adaptive strategy by the host to "immunize" the colony against future exposure to the same pathogenic fungus.
Centre for Social Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Luigi
L
Pontieri
Center for Insect Science, Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, United States of America; Department of Biological Sciences, Rowan University, Glassboro, New Jersey, United States of America.
Svjetlana
S
Vojvodic
Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
Riley
R
Graham
Centre for Social Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Jes Søe
JS
Pedersen
Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
Timothy A
TA
Linksvayer
D000818:Animals; D001000:Ants / Q000276:immunology*; D001522:Behavior, Animal; D052981:Metarhizium; D025282:Mycelium