Urbanization is increasingly transforming the rural and natural environment into an ecosystem that the Earth has never known, and this change is affecting the evolution of life’, concludes lead researcher James Santangelo, of the University of Toronto, in the scientific journal science†
Santangelo collaborated with an almost endless line of co-authors, who read the genetic code of the white clover in one hundred and sixty world cities – a ‘cosmopolitan plant’, in their words. Closer to the city center, the plants, which are also abundant in the Netherlands, turned out to have less active genes for hydrocyanic acid. After all: there are fewer animals in the middle of the city that eat clover, so the usefulness of these genes is limited.
It has been known since the 1950s that certain plant and animal species in the city change shape. The classic example is the birch tree, also known as the pepper-and-salt moth, which at the time became darker in color in English cities: more pepper, less salt. The birches on which the butterflies were sitting were also becoming increasingly black, due to the air pollution.
Urban Ecology
Yet the field of ‘urban ecology’ is only the last ten years strongly emerging. The one study after another appears, showing that urban life does not leave plants and animals untouched. The yellow jasmine in the city, for example, produces more flowers because the pollen is more difficult to spread, the Cardinal’s dot moth is less sensitive to light, swans are less shy and the azure damselfly can fly further because its habitats are further apart.
They are all examples of evolution in a certain city, somewhere in the world. That is what makes the study into white clover, which appeared on Thursday, so innovative: evolution on a global scale was demonstrated for the first time.
‘I think this is an encouraging study’, says Barbara Gravendeel, senior researcher in evolutionary ecology at Naturalis and endowed professor of plant evolution in Nijmegen, herself not involved in the article from science† ‘You usually hear that humans are ruining everything, that species are dying out. But this shows that plant species that have been around for millions of years find a way to interact with humans.’
Seeds up close
It is an advantage for the clover that it does not have to defend itself so actively against gnawing insects in the city. Gravendeel: ‘Life in the city is subject to many disturbances: sometimes it is sweltering hot, then the street is swept again. If plants don’t have to spend energy on making antibodies, they can grow, bloom and make seeds extra fast.’
According to Gravendeel, knowledge about the evolution of urban species can help humans. ‘You now see that such a plant population adapts very quickly. If you are planting new plants or trees in the city, it is therefore advisable to always take seeds from close by. The chance that the young plants will survive is then greater. Ultimately that is also better for humans, because they will not be living among all the dying and desiccated trees in a few years’ time.’