The evolution of animal husbandry by ants

Some ants practise animal husbandry. For example, yellow meadow ants keep root aphids in their nests to eat and for a supply of the honeydew these aphids secrete. Aniek Ivens has been investigating how such cooperation came about in evolutionary terms. She has discovered three characteristics that contribute to successful cooperation – the animals that are ‘husbanded’ are genetically virtually identical, spread hardly at all and reproduce by cloning. Ivens will be awarded a PhD for her research on 23 November 2012 by the University of Groningen.

Aniek Ivens compares the cooperation between the ants and the aphids with the cooperation between humans and dairy cows. ‘The yellow meadow ant lives off the honeydew that the root aphid produces and also eats the aphids as a source of protein. In exchange for these foodstuffs, the ants construct chambers for the aphids and protect them against predators. Over the course of time, the root aphid has evolved to the point that it can no longer survive outside an ant’s nest.’ Previous research at the University of Groningen revealed that this cooperation is not only beneficial to the ants and the aphids, but also influences plant growth near the nests.

Stable cooperation

The cooperation between yellow meadow ants and root aphids is just one of many examples of cooperation – mutualism – in nature. Examples include other ants that cultivate fungi, and in the seas there are numerous cooperations between organisms. The cooperation between humans and their intestinal flora and between humans and their cattle are also examples of mutualism.  

Evolution

‘Scientists have already discovered that mutualism is very important for the stability and resilience of an ecosystem’, says Ivens. ‘However, not much is known about the evolution of mutualism.’ If you follow the standard rules of evolution, you’d think that the stronger species would eventually exploit the other. It would become a sort of parasite. Numerous examples of mutualism, however, show that this theory does not always apply. ‘With my PhD research I have been trying to understand the mechanism of that evolution better’, explains Ivens. She conducted fieldwork, followed by research on genetic relationships. She also used computer models.

Schiermonnikoog

Ivens’s research started on the island of Schiermonnikoog, where she collected three species of root aphids from the nests of the yellow meadow ant. In a laboratory in Copenhagen she investigated the genetic makeup of these aphids. This revealed that the root aphids mainly reproduce by cloning and virtually never spread beyond a single nest. ‘This revealed that the ants were practising a monoculture – they are tending “cattle” that all stem from one clone and that reproduce swiftly. However, they usually have a different clone or species in reserve in a separate chamber.’ Low diversity, limited spread and clonal reproduction has also been found in other examples of mutualism. This is thus probably a precondition for co-evolution, without which the cooperation is not stable.  

Board and lodgings

With the help of a computer model, Ivens simulated the cooperation between two types of bacteria. ‘We assumed in advance that cooperation within a species would only evolve if everyone stayed where they were and continued cooperating well with each other.’ The computer model revealed something completely different, however. ‘We saw that organisms from a population actually leave if the cooperation goes well. They go hunting for a population that cooperates less well and then profit from the advantage they gained from their previous “good” population.’ Another conclusion that Ivens drew from the computer model is that cooperation is successful when the relationship between the costs and benefits of that cooperation is low. That is certainly the case for the root aphid. The aphid produces honeydew as a by-product. The fact that the ants eat this is not disadvantageous for the aphid, plus it gets its board and lodgings in return. That appears to be the ideal circumstances to create a good cooperation relationship.

Curriculum Vitae

Aniek Ivens (Heerlen, 1983) graduated in biology from Wageningen University and in evolutionary biology at the University of Groningen (both with distinction). She conducted her PhD research at the Faculty of Mathematics and Natural Sciences of the University of Groningen. The research was a cooperation between the Theoretical Biology research group at the University of Groningen and the Centre for Social Evolution of the University of Copenhagen. Ivens is currently a member of the National Think Tank 2012, where she is thinking about how to make the food chains in the Netherlands more sustainable. She will shortly be starting follow-up research on her PhD project at The Rockefeller University (NYC, US).

Note for the press

-More information: Aniek Ivens, e-mail a.b.f.ivens rug.nl, a.ivens nationale-denktank.nl

-Short film of an yellow meadow ant 'milking' a root aphid.