After only nine generations, the same plant species is larger and more fragrant if pollinated by bumblebees rather than flies, according to University of Zurich evolutionary biologists Florian Schiestl and Daniel Gervasi.

For their experiments, Gervasi and Prof. Schiestl used the field mustard (Brassica rapa).

They allowed one plant group to be pollinated solely by bumblebees for nine generations, another only by hoverflies, and a third by hand. Afterwards they analyzed the plants, ‘which differed greatly.’

The plants pollinated by bumblebees were larger and had more fragrant flowers with a greater UV color component, which bees and their relatives see.

The plants pollinated by hoverflies, on the other hand, were smaller, their flowers were less fragrant and they self-pollinated considerably more.

“The mechanism of evolutionary change is fact that different pollinators differ in their preferences and thus preferentially cross-pollinate specific plant individuals, much like a plant breeder using individuals with favorable properties,” Prof. Schiestl said.

“The flies’ considerably lower pollination efficiency is the cause of the increase in self-pollination.”

“The plants essentially help themselves if the pollinator transfers too little pollen.”

The fact that the plants change so significantly already after nine generations came as a surprise to the team.

“The traditional assumption is that evolution is a slow process,” Prof. Schiestl noted.

“A change in the composition of pollinator insects in natural habitats can trigger a rapid evolutionary transformation in plants,” he said.

This is particularly interesting as certain pollinator insects such as bees have been vastly decimated by the extensive use of pesticides and the depletion of the landscape in recent decades.

According to Prof. Schiestl, it would thus be conceivable for plants to increasingly rely on flies as pollinators, which would result in the evolution of weaker flower fragrances and more self-pollination. In the longer term, this would reduce a plant population’s genetic variability and the plants would become more susceptible to disease.

The findings will be published this week in the journal Nature Communications.

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Daniel Gervasi & Florian Schiestl. Real-time divergent evolution in plants driven by pollinators. Nature Communications, published online March 14, 2017; doi: 10.1038/ncomms14691

This article is based on text provided by the University of Zurich.