Fossil reveals 48 million year history of zombie-ants

All manner of animals are susceptible to the often deadly body invasion, but scientists have been trying to track down when and where such parasites evolved.

Dr Hughes, from the University’s School of Biosciences, said: “There are various techniques, called a molecular clock approach, which we can use to estimate where and when they developed and fossils are an important source of information to calibrate such clocks.

“This leaf shows clear signs of one well documented form of zombie-parasite, a fungus which infects ants and then manipulates their behaviour.”

The fungus, called Ophiocordyceps unilateralis, appears to take over the mind of infected ants - causing them to leave their colonies and head for a leaf which provides the ideal conditions for the parasite to reproduce.

When the ant gets there it goes into a ‘death grip’– biting down very hard on the major vein of a leaf. This means that when the ant dies, its body stays put so the fungus has time to grow and release its spores to infect other ants.

The death grip bite leaves a very distinct scar on the leaves. This prompted Dr Hughes, together with research partners Conrad Labandeira from the Smithsonian Institution in the USA and Torsten Wappler, from the Steinmann Institute in Germany, to search for potential evidence of the fungus at work by studying the fossilised remains of leaves.

After studying leaf fossils from the Messel Pit, a site on the eastern side of the Rhine Rift Valley in Hesse, Germany, they found clear evidence of the death grip bite in a 48 million-year-old leaf specimen.
 
Dr Hughes said: “The evidence we found mirrors very closely the type of leaf scars that we find today, showing that the parasite has been working in the same way for a very long time.

“This is, as far as we know, the oldest evidence of parasites manipulating the behaviour of their hosts and it shows this parasitic association with ants is relatively ancient and not a recent development.

“Hopefully we can now find more fossilised evidence of parasitic manipulation. This will help us shed further light on the origins of this association so we can get a better idea of how it has evolved and spread.”

The paper, titled Ancient death-grip leaf scars reveal ant-fungal parasitism, is published in the latest edition of Royal Society journal Biology Letters.

The research leading to these results has received funding from the European Community's Seventh Framework Programme under an individual Marie Curie International Fellowship (221041).