Last updated April 12, 2018 at 10:57 am
Scientists have discovered an element of the microbiome that helps leafcutter ants find their way.
Costa Rica Leaf Cutter Ants Working Together Cahuita National Park. Credit: iStock
The way that ants lay down chemical trails for their colony-mates to follow may be the result of a bacterium stored in their poison glands, research suggests.
In seeking to analyse the bacterial colony that lives in and on the leafcutter ant (Atta sexdens rubropilosa) a team of researchers from the University of Sao Paulo in Brazil discovered that one species, Serratia marcescens, when cultured, gave off a smell that strongly resembled that of the ants themselves.
The smell arises from chemical compounds known as “trail pheromones” that the ants lay down to mark out a route to and from the nests.
Ants’ microbiome
The discovery of the bacterium came as a surprise to the researchers, led by Mônica Tallarico Pupo.
The team had set out to try to answer a different question linked to the ants’ bacterial cargo, or microbiome.
Leafcutters are well-known for their habit of slicing up small sections of leaves and then carrying them back to the nests. The leaves are not food for the insects, but serve instead as a substrate on which they cultivate a fungus, Leucoagaricus gongylophorous.
Pupo and colleagues reasoned that because the raw leaf material was not itself microbially sterile, bacteria harmful to both the ants and the fungus must sometimes be carried into the nest. Preventing infection, therefore, must somehow be a function of the microbiome.
To test this idea, the researchers captured a number of leafcutter queens, then transported them and as much of their colonies as possible back to their laboratory.
Bacteria resident on and inside the ants were then captured, isolated, and cultured.
Distinctive aroma
During this process, one of the scientists, Eduardo Afonso da Silva Junior, realised that S. marcescens gave off a distinctive aroma associated with the smell of the ants themselves.
Further investigation revealed that the bacterium produced several aromatic chemical compounds called pyrazines, including one that had never before been recorded.
Given that the microbe and its compounds were found in large numbers inside the ants’ poison glands, it is tempting to suggest that leaf-cutter trail pheromones (and, by extension, the trail pheromones of other ant species) are the result of a previously unsuspected symbiotic relationship between insect and microbe.
Pupo and her colleagues, however, are cautious about drawing the bow that long at this stage of the research.
“Are the trail pheromones produced by bacterium Serratia marcescens or does S. marcescens only help by somehow adding to the whole process?” she asks.
“We intend to investigate in search of answers.
“We don’t know for sure if their synthesis is shared: maybe the microorganism produces the aromatic compounds and the ants store them in their glands.
“In future studies, we plan to test techniques to remove the bacteria from the ants and observe whether the compounds continue to be produced.”
The research is published in the journal Scientific Reports.
