Chemical strategies of social parasites

Dead Acromyrmex queen
An Acromyrmex host queen that tried to walk into a foreign leaf-cutting ant colony was ripped apart by host workers

Social parasites enter social insect colonies and harm their fitness. In case of the leaf-cutting ant parasite Acromyrmex insinuator, the host is essentially castrated. Of course the host colonies try to avoid this type of fate. Their nestmate recognition systems are sensitive enough to detect and reject most intruders (see the image for what happens to an intruding queen). Insects mostly communicate via chemicals, and nestmate recognition is using a chemical blend that is as specific to their colony as a coloured football jersey is to a team.

Social parasites, in turn, often evolved chemical adaptations to bypass host nestmate recognition. One of these adaptations is “chemical camouflage”, where parasites use host chemical substances to “dress” just as host workers, which then take the parasites for one of their own.

Another strategy, termed “chemical insignificance”, consists in parasites not bearing any relevant chemicals: if you met someone without a jersey, you wouldn’t know which team he is on either.

Even though the two strategies have previously been proposed to work in synergy (Bagnères et al 1996 Science 272:889–892; Lenoir et al 2001 Annu Rev Entomol 46:573–599)⁠, they are typically considered separately and researchers try to find out which of the two strategies a parasite uses. In our experiments with Acromyrmex insinuator, we found evidence for both strategies. I think this actually makes a lot of sense and I would expect the two strategies to be synergistic: If you want to dress up as a member of another team, it would be wise not to wear your own jersey under that of the other team because it would look odd and you own jersey may still be spotted. It could be similar for Acromyrmex insinuator parasites: they don’t produce any recognition-relevant substances themselves, so they have it easy to acquire their host-specific nest odour without any interference of a non-fitting odour.

Nehring V, Dani FR, Turillazzi S, et al (2015) Integration strategies of a leaf-cutting ant social parasite. Anim Behav 108:55–65. doi: 10.1016/j.anbehav.2015.07.009


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Variation in the behavioural response to non-nestmates

Behavioural variation in nestmate recognition - caused by different steps in the ant recognition systemLiving in a group has many advantages. One of them is that you don’t have to do everthing yourself. Often, some group members are more likely than others to carry out certain tasks. Perhaps they do it because they are better at the specific task, but maybe only because they are quicker in grasping what needs to be done. Copenhagen Master student Janni Larsen looked at behavioural variation in leaf-cutting ant nest defence behaviour and found that large workers are more likely than small workers to attack intruders. In further experiments we found that the variation was caused by different steps within the ant recognition system: while while large and medium workers were equally good in detecting intruders, but varied in their aggressiveness, smaller workers seemed to be less likely to identify intruders in the first place. Thus, behavioural variation can arise due to different mechanisms.

For a nice intro into the complexity of recognition systems I can recommend the Sherman/Reeve/Pfennig chapter in the 1997 edition of Behavioural Ecology. If you are specifically interested in how Acromyrmex nest defence behaviour varies, please also have a look at a recent article by Bill Hughes’ group.

Larsen, J., Fouks, B., Bos, N., d’Ettorre, P. & Nehring, V. 2014. Variation in nestmate recognition ability among polymorphic leaf-cutting ant workers. Journal of Insect Physiology, 70, 59–66.


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Student assistants wanted

Artificial selection in mites

Poeocilochirus necrophori REM image

Parasitic mite development time is a crucial adaptation to the mite hosts. We will conduct an artificial selection experiment to analyse this trait and its correlation with other important mite traits. I am looking for student assistants who will run the experiment. Daily checks of the mite lines will be required, but these can be shared among multiple students.

Please find more information on the mites and our group at http://evolution.vnehring.de

Tasks:

  • mite breeding & selection

  • behavioural experiments

The position:

  • is open now, for up to six months

  • ca. 20-80 hours/month

  • can be developed into a thesis

  • is payed according to the usual scale, depending on your degree (none/BSc/Msc)

Requirements:

  • passion for scientific research

  • ability to work independently and thoroughly

  • you’ll have to work with mites, breeding them can be smelly at times..
  • experiments have to be attended in weekends as well; otherwise, scheduling is up to you

In case you’re interested in the job, please drop me an email via volker.nehring@biologie.uni-freiburg.de, including a short CV and a letter of motivation.


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Noise in chemical communication

Traffic noise hindering communication
Urban noise -
photo credit: joiseyshowaa via photopin cc

Communication is always constrained by noise. Imagine a finch calling for mates along a busy road during rush hour. Car noise will make it quite difficult for his fellow urban birds to hear him at all. It must be all easier in a peaceful forest, don’t you think? Perhaps not. Forests are full of birds, many of them sing, and not all in the same language. To get the picture, go to a crowded pub or an Italian café (a real one, those with italians;) ). Noise is not necessarily man made pollution, much of what we’d describe as noise in communication is indeed of biological origin. And it’s not restricted to acoustics – there’s noise in any kind of communication, from visual signalling to chemical cues.

Henrik Brumm edited a noise volume for Springer’s Principles of Animal Communication, and Patrizia d’Ettorre, Tristram Wyatt and me contributed a chapter on chemical communication. Unlike in other modalities (most studies on noise deal with acoustic communication), chemical noise has hardly been treated as a phenomenon worth to explicitly investigate. What we could thus mostly do was to collect studies that demonstrate effects which in some way or another are implying noise in communication systems (and how animals deal with it). It has now been a while since the final draft and I came across a few more studies that would deserve their place in a summary of noise in chemical communication, and of course we might have missed some interesting and important phenomena as well. If you’re interested in the topic or think something is missing, please contact me!

Nehring, V., Wyatt, T. D., & d’Ettorre, P. (2013): Noise in chemical communication. In H. Brumm (Ed.), Animal Communication and Noise (pp. 373–405). New York: Springer. doi:10.1007/978-3-642-41494-7_13


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Confirmation bias in behavioural experiments

confirmation bias 11 12 13
12, 13, 14, right?

The data confirmed your expectations? That’s great, you were right from the beginning – or where you tricked by what is called confirmation bias – you only saw what you wanted to see? Although the effect is typically strongest with emotionally charged subjects (think gun control), it can be a serious problem in scientific experiments as well.

Ellen van Wilgenburg and Mark Elgar recently published a great article on the subject. They conducted a meta-analysis of behavioural experiments about nestmate recognition in ants. During these experiments, ants were encountered with other ants who were either nestmates or non-nestmates. In such situations, nestmates are typically treated peacefully while non-nestmates are attacked.

The authors found a clear difference between studies where the experimenter knew whether the ants they observed were nestmates or non-nestmates, and other studies where the experimenter did not have this information, i.e. was blind to the origin of the ants. Studies with blind experiments were more likely to find aggression between nestmates, and the difference between nestmate and non-nestmate aggression was lower in blind than in non-blind experiments. Apparently, researchers are more likely to score a behaviour as aggressive when they expect aggression, and tend to “overlook” aggression when no aggression is expected.

It may seem odd to you to find aggression between nestmates, because if that occurred in nature, life in ant colonies would be quite chaotic. However, as experiments rarely track natural conditions very closely and the ants are under some stress during the tests, recognition errors may occur.

confirmation bias ABC / 11 12 13
Or was it 12, B, 14? You expected a number, you saw the 13 – expectations influence perception.

Isn’t this study by van Wilgenburg and Elgar pretty much what many of us who routinely conduct behavioural experiments always thought someone should do? So read it, give it to your students, and do your experiments blindly!

van Wilgenburg E, Elgar MA (2013) Confirmation Bias in Studies of Nestmate Recognition: A Cautionary Note for Research into the Behaviour of Animals. PLoS ONE 8(1): e53548. doi:10.1371/journal.pone.0053548


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Wingless warrior queens in the media III

Acromyrmex working queen article in The Acromyrmex queens made it to Austria, and some more newspapers printed articles:


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Wingless warrior queens in the media II

Article about warrior queens in the newspaper Darmstädter EchoThere are still some people picking up our story on wingless Acromyrmex queens. First of all, Mischa Dijkstra wrote a nice little highlight in his blog. Then an article has been printed on the Science pages of the newspaper Darmstädter Echo (German). And further there is a bunch of articles in all kinds of languages, possibly triggered by the story being published by the European Commission’s CORDIS service in English, Spanish, French, Italian, Polish, and German.


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Wingless warrior queens in the media

New Scientist on wingless warrior queens in Acromyrmex (Nehring et al. 2012)Our article on wingless virgin queens that defend their colonies received quite some attention by the media, in particular in Germany. Among the english language websites that covered the story were The New Scientist and Science Daily:

Wingless virgin Acromyrmex queens on the WELT front pageGerman Print Media

German Online Media

Other languages:


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New paper: Wingless virgin queens defend leaf-cutting ant colonies

Aggressive wingless Acromyrmex queenI have a new paper published on nest-defence in Acromyrmex leaf-cutting ants. We found that young virgin queens switch to worker behaviour once they lose the prospect of founding their own colony. Normally, virgin queens avoid taking risks because they are supposed to partake in a mating flight and found a new “daughter” colony afterwards. Sometimes, however, the young queens lose their wings (probably by accident) before they can leave the nest. Then, they cannot fly and mate any more, and the only way to boost their fitness is by directly helping the colony, just like workers do.

V Nehring, JJ Boomsma, P d’Ettorre (2012): Wingless virgin queens assume helper roles in Acromyrmex leaf-cutting ants. Current Biology 22: R671-R673, doi:10.1016/j.cub.2012.06.038.

Media coverage

More media coverage

Even more media coverage

Press releases:

Amazon-like female warriors protect societies of farming ants

Princesses become warriors: Young queens of leafcutter ants change roles if they cannot reproduce (University of Freiburg)

Amazone-agtige krigere forsvarer svampedyrkende myresamfund (Danish, Copenhagen University)


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