Science: Vaccination by kissing

Everyone knows that when you’re sick, you shouldn’t kiss or have too much contact with other people (unless you intentionally want to make them sick). In ants, this works in an entirely different way.

If you get sick, your immune system will make antibodies against this specific disease. These antibodies will defend you in case this disease comes back, making it less likely you will get sick again (this is also the basis of vaccination).

Many ants frequently appear to be kissing with eachother. In scientific terms this is called stomodeal trophallaxis, meaning mouth-to-mouth feeding. This way, only a couple of ants have to go out and get food, after which they can spread it through the colony by trophallaxing with hungry individuals. This function of the ant ’kisses’ has been known for a long time.

Formica exsecta ants exchanging food by trophallaxis

Formica exsecta ants exchanging food by trophallaxis

Recently however, Casey Hamilton and coworkers have found a new function of trophallaxis. The researchers made two groups of ants. One group was very hungry, while the other group was well fed. The well fed ants were ’vaccinated’ against bacteria. Now, these ants had, next to food, a lot of substances that kill bacteria in their body (called anti-microbial peptides).

Once the hungry ants and the vaccinated, fed ants came together, trophallaxis occurred as the fed ants spread the food to the hungry ones.

Now comes the cool part. After the hungry ants were fed by the vaccinated ants, the researchers exposed the hungry ants to bacteria. While these ants should die because of the disease, it appeared they were now more resistant to it than before. Conclusion: ants can spread their ’immunity’ to other individuals while exchanging food.

Hamilton, C., Lejeune, B.T., Rosengaus, R.B. (2010). Trophallaxis and prophylaxis: social immunity in the carpenter ant Camponotus pennsylvanicus. Biology letters 7, 89-92

Further reading:
Ugelvig, L.V., Cremer, S. (2007). Social prophylaxis: Group interaction promotes collective immunity in ant colonies. Current Biology 17, 1967-1971

Konrad, M et al. (2012). Transfer of pathogenic fungus promotes active immunisation in ant colonies. PLoS Biology 10(4) e1001300

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