Ants treat their sick and keep pathogens in check
Researchers in Germany and Austria have successfully demonstrated how micro-infections promote social vaccination in ant societies. Presented in the journal PLoS Biology, the study was supported in part by two EU-funded projects: SOCIALVACCINES and LATENTCAUSES. Both SOCIALVACCINES ('Social vaccination in ant colonies: from individual mechanisms to society effects') and LATENTCAUSES ('Modelling latent causes in molecular networks') were funded under the European Research Council (ERC) of the EU's Seventh Framework Programme (FP7) to the tune of EUR 1.3 million and EUR 1.24 million, respectively.
Researchers led by the Institute of Science and Technology Austria (IST Austria) investigated the potential of disease outbreaks in ant colonies. Experts say the ants' social immune system works at helping ensure such outbreaks are kept at bay. The system in question is a set of collective hygienic behaviours and adaptive changes in interaction frequencies that acts together with the physiological, innate immune system of colony members. The results generated by Professor Sylvia Cremer and her team will give researchers the information they need to understand how taking care of sick ants leads to better disease protection within their society.
Contrary to what humans do, ants do not stay away from colony members that are ill. Instead, they go to them, licking them to remove the pathogen from the exposed ant's body. Because of this social grooming behaviour, the sick ants have a much better chance of surviving compared to those who are not treated. The downside, however, is that the helper ants increase their risk of being inflicted with the disease.
The researchers applied fluorescence-labelled fungal spores to some ants and allowed them to interact with healthy colony members. The labelled spores spread throughout the colony. But the team observed that spore transfer occurs at very low levels, triggering just sublethal micro-infections in the previously healthy colony members.
According to the researchers, these low-level infections stimulate the expression of a specific set of immune genes and intensify the ants' ability to fight the fungal pathogen. This social immunisation increases a colony's ability to recover more quickly from an infection.
The team said the social low-level spread of infectious particles plays a fundamental role, representing the underlying mechanism of social immunisation against fungal infections in ant societies.
'We found that these low-level infections per se, even in the absence of social contact, are necessary and sufficient to explain the increased antifungal activity of nestmates. We found no evidence for visual or volatile chemical cues acting as additional trigger signals for the immune stimulation of the nestmates. Furthermore, neither ant behaviour nor physiology gave an indication for passive nestmate immunisation via transfer of antimicrobials from either exposed ants or their nestmates to the other group members. Finally, experimental elimination of the active route resulted in the absence of protective antifungal activity in nestmates.'
Experts from the Institute of Bioinformatics and Systems Biology of the German Research Center for Environmental Health, and the Institute of Evolution, Behaviour and Genetics of Universität Regensburg in Germany contributed to this study.