Inbreeding affects ant hygiene

Inbreeding reduces the ability of ant colonies to respond to fungal infections, scientists report this week in Proceedings of the Royal Society B.  Researchers based in Regensburg and Cambridge studied colonies of Brazilian Cardiocondyla obscurior ants infected by the pathogenic fungus Metarhizium anisopliae.

The ants have a highly variable social structure in the wild, which makes them ideal for studying the effects of genetic diversity; while some colonies have only one queen and are highly inbred, other colonies are genetically diverse because they have multiple queens and interbreed with other colonies.

Ants have a number of ways to fight infections, including immune system defences and grooming.  However, the researchers also discovered that ants also actively disinfect their nests, by removing diseased larvae from the brood and discarding them.  This is the first time such “hygienic” behaviour has been observed in ants and it turns out to be the key to the difference between inbred and diverse colonies’ reactions to infection.

While ants from both types of colony actively remove diseased larvae, the timing is crucial.  Ants from genetically diverse colony tend to remove diseased larvae within 24 hours of infection, while inbred ants do so much later.  This means that the inbred ants suffer from higher infection rates as the fungus has longer to proliferate and infect other larvae.

It is not clear exactly why the ants from diverse colonies are so much better at keeping their nests hygienic, but the authors suggest that it may be due to impaired pathogen detection capabilities of the inbred ants.  While it has long been known that the susceptibility of individuals to disease is strongly related to genetics, the relation between group-level disease resistance and individual physiological and behavioural defences remains poorly understood.  This study represents a significant development in the field and the authors hope that it will lead to further advances, particularly in the understanding of the mechanisms behind disease detection in ant communities.