Biologist Nick Bos tells Wikinews about ‘self-medicating’ ants

Tuesday, September 1, 2015

Nick Bos, of the University of Helsinki, studies “the amazing adaptations social insects have evolved in order to fight the extreme parasite pressure they experience”. In a recently-accepted Evolution paper Bos and colleagues describe ants appearing to self-medicate.

The team used Formica fusca, an ant species that can form thousand-strong colonies. This common black ant eats other insects, and also aphid honeydew. It often nests in tree stumps or under rocks and foraging workers can sometimes be spotted climbing trees.

Some ants were infected with Beauveria bassiana, a fungus. Infected ants chose food laced with toxic hydrogen peroxide, whereas healthy ants avoided it. Hydrogen peroxide reduced infected ant fatalities by 15%, and the ants varied their intake depending upon how high the peroxide concentration was.

In the wild, Formica fusca can encounter similar chemicals in aphids and dead ants. The Independent reported self-medicating ants a first among insects.

Bos obtained his doctorate from the University of Copenhagen. He began postdoctoral research at Helsinki in 2012. He also runs the AntyScience blog. The blog aims to help address “a gap between scientists and ‘the general public’.” The name is a pun referencing ants, its primary topic, science, and “non-scientific” jargon-free communication. He now discusses his work with Wikinews.

((Wikinews)) What first attracted you to researching ants?

Nick Bos Me and a studymate were keeping a lot of animals during our studies, from beetles, to butterflies and mantids, to ants. We had the ants in an observation nest, and I could just look at them for hours, watching them go about. This was in my third year of Biology study I think. After a while I needed to start thinking about an internship for my M.Sc. studies, and decided to write a couple of professors. I ended up going to the Centre for Social Evolution at the University of Copenhagen where I did a project on learning in Ants under supervision of Prof. Patrizia d’Ettorre. I liked it so much there I ended up doing a PhD and I’ve been working on social insects ever since.

((Wikinews)) What methods and equipment were used for this investigation?

NB This is a fun one. I try to work on a very low budget, and like to build most of the experimental setups myself (we actually have equipment in the lab nicknamed the ‘Nickinator’, ‘i-Nick’ and the ‘Nicktendo64’). There’s not that much money in fundamental science at the moment, so I try to cut the costs wherever possible. We collected wild colonies of Formica fusca by searching through old tree-trunks in old logging sites in southern Finland. We then housed the ants in nests I made using Y-tong [aerated concrete]. It’s very soft stone that you can easily carve. We carved out little squares for the ants to live in (covered with old CD covers to prevent them escaping!). We then drilled a tunnel to a pot (the foraging arena), where the ants got the choice between the food with medicine and the food without.

We infected the ants by preparing a solution of the fungus Beauveria bassiana. Afterwards, each ant was dipped in the solution for a couple of seconds, dried on a cloth and put in the nest. After exposing the ants to the fungus, we took pictures of each foraging arena three times per day, and counted how many ants were present on each food-source.

This gave us the data that ants choose more medicine after they have been infected.

The result that healthy ants die sooner when ingesting ROS [Reactive Oxygen Species, the group of chemicals that includes hydrogen peroxide] but infected ants die less was obtained in another way (as you have to ‘force feed’ the ROS, as healthy ants, when given the choice, ignore that food-source.)

For this we basically put colonies on a diet of either food with medicine or without for a while. And afterwards either infected them or not. Then for about two weeks we count every day how many ants died. This gives us the data to do a so-called survival analysis.

We measured the ROS-concentration in the bodies of ants after they ingested the food with the medicine using a spectrophotometer. By adding certain chemicals, the ROS can be measured using the emission of light of a certain wave-length.

The detrimental effect of ROS on spores was easy to measure. We mixed different concentrations of ROS with the spores, plated them out on petridishes with an agar-solution where fungus can grow on. A day after, we counted how many spores were still alive.

((Wikinews)) How reliable do you consider your results to be?

NB The results we got are very reliable. We had a lot of colonies containing a lot of ants, and wherever possible we conducted the experiment blind. This means the experimenter doesn’t know which ants belong to which treatment, so it’s impossible to influence the results with ‘observer bias’. However, of course this is proof in just one species. It is hard to extrapolate to other ants, as different species lead very different lives.

((Wikinews)) Where did the ants and fungus you used come from? How common are they in the wild?

NB For ants, see above about the collection.

This species of fungus does appear in Finland, but we chose to use a different strain from Denmark (with thanks to Prof. J. Eilenberg and the laboratory technician Louise Lee Munch Larsen from the University of Copenhagen). Animals can adapt to local strains (‘local adaptation’), and just to make sure we thought it would be good to use a strain of fungus that the ants definitely did not evolve specific resistances against. This means that the reaction of the ants (to self-medicate) is very likely to be a general response, and not just against their local fungal enemies.

((Wikinews)) Are there any ethical considerations around exposing ants to toxins and parasites?

NB Legally, no. Insects do not have any ‘rights’ as such regarding ethics. That said, we do take measures to not make them ‘suffer unnecessarily’. For example, dissections are done when the ants are anesthetized (either by CO2 or Ice), and when ants need to be killed, we do it in alcohol, which kills the ants in a matter of seconds. So while the ants do not have ‘rights’ as such, we still try to handle them with as much respect as possible (even though the experiment involves infecting them with a deadly fungus).

But even though the 12,000 ants in our study sounds like a lot (and it is), this is negligible in the ‘grand scheme of things’. It has been calculated that in the Netherlands alone, nearly a trillion insects die against just the licence-plates of cars every six months. I don’t own a car, so that means I’m excused right? 😉

((Wikinews)) This is the first evidence for self-medicating insects. How widespread do you think this phenomenon could be in reality?

NB It’s not actually the first evidence for self-medication in insects. Moths and fruit flies definitely do it, and there’s evidence in honey bees and bumble-bees as well. So it seems to be quite wide-spread in the insect world. I have no doubt that as time goes on, there will be more and more cases documented. Insects (and animals in general) seem to be quite good at taking care of themselves.

((Wikinews)) How might ants locate healing substances in the wild?

NB Very good question. This is something that’s important to know. If they would only do it in the lab, the behaviour wouldn’t be very interesting. We have some guesses where they might get it from, but at the moment we don’t know yet. That said, I plan to investigate this question (among others) further [in] the next couple of years.

((Wikinews)) For your PhD you researched ants’ scent-based communications. Could healthy ants perhaps tell other ants are infected and encourage this behaviour?

NB There’s not much known about this. There’s conflicting evidence about whether sick ants actually smell different from healthy ones or not. At the moment it seems that sick ants mostly take care of the problem themselves. Sick ants stop most interaction with nestmates and especially brood, and leave the nest to die in isolation. This is probably for reducing chance of infecting nestmates, but of course it also reduces the work load of their nest-mates, as their corpse doesn’t have to be dragged out etc.

So as an answer to the question, I would find it unlikely that such a behaviour would evolve, but it’s not known yet.

((Wikinews)) Ants generally avoided the peroxide if they were healthy, but in some circumstances might they try to build resistance against infection in advance?

NB Who knows? Also not known yet unfortunately. That said, there is a very interesting study about resin collection in ants. Wood ants collect tree-resin, which has anti-microbial properties. They collect this even if not infected, and when you infect them, they don’t collect more of the resin than normal. So basically it seems like they collect it in order to keep diseases out of the nest, so they stop the disease before it can actually infect them.

((Wikinews)) Are there plans to follow this research up? Might you research other species? Other substances?

NB I first want to find out where they get it from in nature. There might be many sources of medicine (recent evidence suggests that tobacco plays a similar role for bumble bees). Dalial Freitak, who is also on this paper is currently running tests with Ph.D. student Siiri Fuchs (who is also on the paper) with other substances to see if any have the same effect as H2O2 [hydrogen peroxide].

Once the behaviour has been well described in this species of ant, I might do a comparison with other species. For example, once we find the source of the medicine in nature… would species without access to this source also have evolved the same behaviour in the lab? And if so… where would they get it from?

Also… can ants medicate their friends? 🙂

((Wikinews)) What other research are you working on right now?

NB Phew…lots! 🙂

I still have some questions left unanswered from my Ph.D. work related to how ants recognize who is a friend and who isn’t. I also started collaborating with Prof. Michael Poulsen from the University of Copenhagen on immunity in fungus-growing termites, as well as their chemical recognition abilities. Furthermore we’re working on social parasitism in wood-ants (ants have lots of animals exploiting the nest for shelter and resources, which all somehow have to get in to the fortress without getting killed).