Nehring lab

Large societies of ants and humans have standing armies with professional soldiers, but smaller societies usually rely on conscription when they are threatened. Leaf-cutting ant societies of intermediate size have evolved the peculiar practice of turning daughter queens that failed to mate and disperse into life time nest-defenders, reminiscent of mythical female warriors whose normal reproduction was impaired by their unusual military careers.

New research of the Centre for Social Evolution at the Department of Biology, University of Copenhagen shows that some societies of leaf-cutting ants produce daughter queens that can either leave the nest on wings to mate and found a new colony (as the large majority of ants do) or become virgin queen soldiers when their normal reproductive future fails. These societies are too small to maintain a specialized soldier caste, but since queens are considerably larger than workers they make good soldiers in the event of an attack.

 Female soldiers are uncommon in human history, but normal in ant societies, in which only the females work and defend the nest. Mythological societies such as the Amazons living around the Black Sea and the Valkyries or shieldmaiden in ancient Germanic and Nordic sagas emphasize that women-soldiers start their careers as virgins, and Herodotus claims that no Amazon girl was allowed to marry before she had killed a man in battle. Also otherwise, it is hard to escape the notion than these women remained somewhat reproductively handicapped for the rest of their lives. Hippocrates writes that Amazons have no right breasts, so the muscles of their right arm and shoulder could develop more strongly. Other versions of the myth claim that male residence and normal sexual relationships were forbidden in Amazon territory, so that reproduction required very special measures.

In the ant-societies the scientists observed virgin daughter queens in soldier roles in the field (Panama), and they decided to experimentally force virgin daughter queens to stay home by removing their wings to see how this would change their behaviour.

Wingless daughter queens modified their behaviour in two different ways: they began to take care of the colony’s brood and were unusually motivated to fight with intruders, unlike normal virgin queens that try to get away and leave their worker sisters with the dangerous defence tasks. Hiding from danger makes perfect sense, because ants pass on most of their genes to future generations by only a few “shy” but fertile queens that are well protected by many sterile and aggressive workers.

 The switch in daughter queen behaviour is remarkable, because they change from a queen-like to a worker-like behavioural program by the simple event of losing their wings. It is as if they know that wing-loss implies that they will stay virgin forever and never be able to reproduce as queen, so all they can do is offer a bit of help to their intact queen sisters who can still pass on the colony’s genes. In all other ants studied so far, failed queens are simply killed and cannibalized by their sisters to recycle the resources that are stored in their bodies. CSE researchers speculate that one of the reasons why such cannibalism does not happen in leaf-cutting ants is that these ants farm fungi for food in underground gardens so they have lost the ability to digest meat.

It normally only pays ant societies to maintain a specialized caste of soldiers when their societies are big, similar to large human nations tending to have more massive armies with better tanks and warships. Soldier ants can therefore be observed in warmer climates but not in North-west Europe, where ant nests only become moderately large, so the normal workers need to take care of defence tasks. It seems that the fungus-growing ants have discovered a third way to secure effective colony defence by making failed queens adopt defender roles for which they were never intended, but for which they are well suited due to their body size. It is interesting that developing an ant soldier career is directly connected to impaired reproduction, similar to what myths tell us about the few historical societies from which women were known to pursue military careers.

Article:

Nehring, V., Boomsma, J.J. & d’Ettorre, P. (2012): Wingless virgin queens assume helper roles in Acromyrmex leaf-cutting ants. Current Biology 22: 671-673 doi:10.1016/j.cub.2012.06.038.

 Contact details:

 Dr. Volker Nehring, Centre for Social Evolution, University of Copenhagen. Currently at University of Freiburg, Germany: Volker.Nehring@biologie.uni-freiburg.de, Phone +49 761 203 8346

Professor Jacobus J. Boomsma, Centre for Social Evolution, University of Copenhagen, Denmark: JJBoomsma@bio.ku.dk, Phone +45 353 213 40 or +45 204 367 71

 Professor Patrizia d’Ettorre, Centre for Social Evolution, University of Copenhagen, Denmark & Laboratory of Experimental and Comparative Ethology, University of Paris 13 – Université Sorbonne Paris Cité, France: Patrizia.dEttorre@leec.univ-paris13.fr, Phone: +33 665 163 200

In social insect colonies, workers generally cooperate within extended families consisting of full- and half-sisters. It has been suggested that they do not behave nepotistically, i.e. prefer to cooperate with full-sisters only, because they are not able to distinguish between half- and full sisters Actually, some ant species might know better, as researchers from Denmark, France, and the UK now found out.

Social insect societies are generally seen as nature’s finest example for cooperation. To help their mother queen, workers forego producing own offspring to increase the number of siblings their mother can rear, some of which will become new queens. In this way, the workers pass on their genes through siblings instead of offspring. Researchers therefore believe that high relatedness among colony members was important in the evolution of social insect colonies.

In some social insect species, the queens mate with more than one male, and hence not all of the workers are full sisters. Instead, several genetic lineages exist inside a single colony, with workers being full sisters within, but only half sisters between the lineages. Each worker would have a better chance of passing on its genes if it could preferentially help full-sisters rather than half-sisters, but the colony as a whole would be less efficient as a result of these internal power struggles.

Previously it has been thought that workers were not able to act nepotistically because they had no information that would allow them to discriminate between full- and half-sisters. By obscuring genetically based recognition cues, the colony would be safe from harmful struggles between worker lineages. Now, researchers from the Centre for Social Evolution (Universitiy of Copenhagen), and the Universities of Leeds and Paris 13, analysed both the odours of leaf-cutting ant workers and their genetic relatedness. They found that chemicals on the ants’ bodies are specific to the different genetic full-sister lineages within colonies. These chemicals, cuticular hydrocarbons, make up odours that were already known to be used for recognition by ants in other contexts, such as defending their nest from enemies. It is therefore likely that an ant can smell the difference between a full and a half sister, and in principle also use this information to preferentially help full sisters. This result demonstrates how much potential for conflict there is even in those insect societies that are seemingly governed by harmonious cooperation.

 Nehring,V., Evison, S.E.F, Santorelli, L.A., d’Ettorre, P. & Hughes, W.O.H: Kin-informative recognition cues in ants. Proceedings of the Royal Society B, online early 1.12.2010

Hos sociale insekter, blandt andet hos myrer, har man hidtil antaget, at alle individer i en koloni samarbejder lige godt. Forskere på Københavns universitet og kolleger i Frankrig og Storbritannien har nu vist, at nepotisme måske også dyrkes blandt sociale insekter.

Den harmoniske samfundsstruktur hos sociale insekter står ofte som et af naturens fineste eksempler på samarbejde.

I visse kolonier hjælper arbejderne dronningen med at lægge æg. På den måde sørger arbejderne for at producere søskende og hjælpe dronningen med at skabe en koloni baseret på familiemedlemmer med samme gener. På denne baggrund mener forskere, at et slægtskab mellem koloniens medlemmer er vigtigt i udviklingen og opretholdelsen af en stærk koloni.

I andre sociale kolonier parrer dronningen sig imidlertid med mere end én han. Dette gælder blandt andet hos bladskærer-myrer. Her består kolonien både af søskende og halv-søskende, – altså af arbejdere med forskelligt slægtsforhold og forskellige gener.

Tidligere har man ikke haft mistanke til nepotisme i disse kolonier, men forskere fra Center for Social Evolution, Biologisk Institut på Københavns Universitet har sammen med universiteter i Leeds og Paris opdaget, at bladskærer-myrer har specielle duftkirtler, som udsender en duft, der er genetisk betinget.

Ikke blot har disse dufte vist sig at være nyttige for at holde andre myrer væk fra en koloni, men det er også muligt, at duftene desuden spiller en rolle internt i en koloni til at skelne søskende fra halv-søskende.

Det er højst sandsynligt, at en myre kan lugte forskel på søskende og halvsøskende – og i princippet bruge disse oplysninger til at hjælpe de søskende, der har de samme gener. Resultatet viser også, at selv i et harmonisk samfund som insektsamfundet, ligger familiekonflikter på lur.

Videnskabelig artikel:

Nehring,V., Evison, S.E.F, Santorelli, L.A., d’Ettorre, P. & Hughes, W.O.H: Kin-informative recognition cues in ants. Proceedings of the Royal Society B, online early 1.12.2010

Yderligere information:

Ph.d. studerende Volker Nehring, Center for Social Evolution, Biologisk Institut, Københavns Universitet, mail: VNehring@bio.ku.dk, tlf. 3532 1280 eller kommunikationsmedarbejder Helle Blæsild, tlf. 2875 2076

Myrer er ikke i tvivl: Hvem skal lukkes ind, og hvem skal ikke? Har du den forkerte duft kan det betyde en kamp på liv og død, mens myrer med samme duft lukkes ind i myretuens beskyttende fællesskab, viser ny forskning fra Biologisk Institut ved København Universitet.

See the entire press release (in Danish!)  on ku.dk