Ants kill colony mates infected with deadly diseases when they are unable to prevent them from falling sick in the first place. In doing so, the ants protect their colony from the outbreak of an epidemic. When fighting diseases, ant colonies show a remarkable similarity with the immune system that protects the organism of vertebrate animals. This is the result of a study carried out by researchers at the Institute of Science and Technology Austria (IST Austria), first author and PhD student Christopher Pull and Professor Sylvia Cremer as the senior author, along with collaborators at Royal Holloway, University of London and the University of Würzburg. The study is published today in the journal eLife.
When an ant comes into contact with the pathogenic fungus Metarhizium, it has the potential to harm the entire ant colony. This is because infectious diseases can spread easily among colony members, who live closely together, and may lead to the death of the entire colony if infections are not contained. Sylvia Cremer and her group have previously shown that invasive garden ants (Lasius neglectus) care for colony members carrying pathogenic fungus spores by intensively grooming the contaminated individual's body, which reduces the risk of the fungus entering the body and infecting the ant. But how do ants act when the grooming ants are not successful and an ant becomes infected with the disease? Sylvia Cremer and Christopher Pull, along with their collaborators at Royal Holloway, University of London and the University of Würzburg, investigated this question in their current study published in eLife.
Whilst ants care for pathogen exposed brood, the response to an infection is much more radical: in a series of experiments, the researchers found that the ants kill fungus-infected pupae to stop the pathogen completing its lifecycle, so that it cannot spread any further. The ants act selectively: they detect animals that are already fatally infected using chemical "sickness cues" and kill them. "We found that the ants are able to smell and single out sick colony members very early on in the infection process. They then perform what we have termed "destructive disinfection", the killing of the sick animal and the fungus, to prevent the pathogen becoming contagious and spreading to nestmates", explains Sylvia Cremer.
This destructive disinfection has remarkable parallels with the immune system of vertebrates. Infected cells in a body send out a signal that attracts immune cells. These then make holes in the infected cell to inject toxic substances that kill both the cell and the pathogen. Something very similar happens in Lasius neglectus, as Christopher Pull describes: "The ants produce formic acid that can kill the fungus, but it needs to enter the pupa's body for it to work. During destructive disinfection, the ants therefore remove pupa's silk cocoon and bite holes in its body. They then spray their formic acid through these holes, so that it enters the pupa's body and kills the pupa along with the fungus". Sylvia Cremer explains where this similarity may come from: "Ants in a colony work together like the cells in a body, and colonies are sometimes even referred to as 'superorganisms'. In our study, we show the remarkable parallels between the immune responses of ant colonies and that of vertebrate bodies. The ability to detect and destroy harmful elements was likely necessary for the evolution of both multicellular organisms from single celled life and superorganisms from individual animals."
Christopher Pull, first author of the study, was a PhD student in the group of Sylvia Cremer at IST Austria from 2012 to 2017. He is now a postdoctoral researcher at Royal Holloway, University of London. Sylvia Cremer investigates social immune defences in ants to learn more about epidemiology and disease dynamics in societies.
About IST Austria -- http://www.ist.ac.at
The Institute of Science and Technology (IST Austria) is a PhD-granting research institution located in Klosterneuburg, 18 km from the center of Vienna, Austria. Inaugurated in 2009, the Institute is dedicated to basic research in the natural and mathematical sciences. IST Austria employs professors on a tenure-track system, postdoctoral fellows, and doctoral students. While dedicated to the principle of curiosity-driven research, the Institute owns the rights to all scientific discoveries and is committed to promote their use. The first president of IST Austria is Thomas A. Henzinger, a leading computer scientist and former professor at the University of California in Berkeley, USA, and the EPFL in Lausanne, Switzerland. The graduate school of IST Austria offers fully-funded PhD positions to highly qualified candidates with a bachelor's or master's degree in biology, neuroscience, mathematics, computer science, physics, and related areas.
About Royal Holloway, University of London -- royalholloway.ac.uk
Royal Holloway, University of London, is ranked in the top 30 universities in the UK and the top 200 universities in the world . Through world class research that expands minds and changes lives, the dedication of our teachers and the feel of the Royal Holloway experience, ours is a community that inspires individuals to succeed academically, socially and personally.
The university was founded by two social reformers who pioneered the ideal of education and knowledge for all who could benefit. Their vision lives on today. As one of the UK's leading research-intensive universities we are home to some of the world's foremost authorities in the sciences, arts, business, economics and law. We are strengthened by diversity, and welcome students and academics who travel from all over the world to study and work here, ensuring an international and multi-cultural perspective within a close knit and historic campus.
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