Abstract
The origin and effects of an evolutionary game between species from three different kingdoms (plants, fungi and animals) are presented. We provide scientific evidence that the interaction discovered in man-made habitats leads to an early stage of coevolution. The grass Puccinellia distans was observed to rapidly spread in new man-made habitats, while at the same time, it was colonised by the fungus Epichloë typhina. The invasion of infected grasses is accompanied by alterations in life histories of both species: P. distans developed features promoting long-distance spreading, whereas E. typhina changed its life cycle by forming sexual structures for the second time, later in the vegetative season. This enables the fungus to make use of the late shoots of the grass for sexual reproduction, even though it cannot be completed because the vector of spermatia necessary for fertilisation, female Botanophila flies, is not present at that time. This indicates that such uncoordinated evolutionary processes had taken place before interactions between organisms became so specialised that it is difficult to presume they were the result of natural selection. Moreover, these processes could have been initiated in man-made habitats that, in particular circumstances, can become coevolutionary hotspots.