Climate Change: Flowers Are Abandoning Pollinators

Camille Moreau with AFP / Photo credit: 15:43 p.m., December 20, 2023

The decline in the number of pollinating insects, such as bees and bumblebees, is causing flowers to do without them: a vicious circle that is harmful to these animals as well as to crops, according to a study published Wednesday. "A lot of experimental work shows that in the absence of pollinators, we have a decrease in the size of flowers and their nectar production," Samson Acoca-Pidolle, a PhD student at the University of Montpellier, told AFP.

Disruption of interaction with pollinators

But what is "truly innovative is that we have shown in the natural environment an evolution of plants towards a break in their interaction with pollinators over the last 30 years," continues the first author of the study published in New Phytologist. The team from the Centre for Functional and Evolutionary Ecology (CEFE) looked at the fate of field thinking (Viola arvensis) and its pollinators, at four sites in the Paris region. She relied on a technique of "resurrection ecology", which involves comparing contemporary flowers with those whose seeds were collected from the same sites more than 20 years ago and kept in national botanical conservatories.

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As a result, in this Paris region, where the number of pollinators is declining sharply, today's flowers are 10% smaller and produce 20% less nectar than their close ancestors. This is not surprising, since "as soon as the nectar is no longer useful, if there are no more pollinators, there is no point in producing them because it is just a cost for the plant," explains Pierre-Olivier Cheptou, CNRS research director at CEFE and co-author of the study. The decline of flying insects has been documented in many parts of Europe, due to intensive agriculture, pollution and climate change.

"Evolutionary cul-de-sac"

The CEFE study indicates that this decline affects a co-evolution of several million years with flowering plants in record time. For the wild thoughts of study are not content to save their strength. They redirect them towards self-fertilization, a phenomenon in which "each plant reproduces with itself," continues Pierre-Olivier Cheptou. Some 80% of flowering plants have this ability and "a large part" could therefore "evolve towards self-fertilization" in the absence of pollinators, says Samson Acoca-Pidolle.

This would be far from a panacea. Firstly, because the process would represent an "evolutionary dead end, quite irreversible", according to Pierre-Olivier Cheptou, since with a very homogeneous genetic heritage, "you have fewer possibilities of adaptation". The second consequence is more immediate and is expected to affect crops. Wild pansies are messicultural plants, i.e. present in agricultural crops, such as rapeseed or sunflower. By attracting pollinators, they promote pollination.

The pollinator, the big loser

The big loser in the affair remains the pollinator, victim of a real vicious circle. Its decline causes plants to produce less nectar and therefore to make its food source scarce, which further threatens its survival and causes plants to do without it.

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The phenomenon also has serious consequences for certain flowering plants in grasslands with several species. According to Pierre-Olivier Cheptou, researchers have observed a "scarcity of plants that are pollinated by insects, in favor of species that are more self-pollinating." The results are "quite worrying", according to Samson Acoca-Pidolle. Who wonders: "Can we go back to the previous state by stopping putting pressure on pollinators, or is this interaction with flowers lost forever?"