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Ancient, interdependent relationships that contribute to food systems and ecosystem stability around the globe may be changing.
Many flowering plants can pollinate themselves, or transfer pollen between their own flowers to generate and propagate seeds, but most of these plants rely on pollination such as butterflies and bees to reproduce.
Now — amid reported declines in many pollinator populations — a new study of the evolution of the mating system of one flower species has revealed a significant change that could exacerbate the challenges facing the plants’ insect partners.
The reproductive evolution of flowers may be linked to environmental changeslike habitat destruction and continuous rapid reductions in pollinator biodiversity, according to Samson Acoca-Pidolle, who led the study published December 19 in the journal New Phytologist.
Comparing seeds of wild field pansies collected decades ago in France with the modern offspring of the plants, Acoca-Pidolle and his colleagues found that today’s flowers are smaller and produce less nectar as a result on increased self-pollination, which has a direct impact on pollinator behavior. . According to the study, pansies of the past did not self-fertilize less and attracted many more pollinators than those of the present.
“It seems that only the characteristics of plant-pollinator interactions are evolving,” said Acoca-Pidolle, a doctoral researcher at the University of Montpellier. The changes could limit the ability of plants to adapt to future environmental changes and could have implications for “all floral biodiversity” – potentially reducing genetic, species and ecosystem diversity flowering plants.
“This could increase the decline of pollinators and create a vicious feedback cycle,” study co-author Pierre-Olivier Cheptou told CNN. If plants produce less nectar, there will be less food available for pollinators, which will accelerate the rate at which animal numbers will decline, he explained.
“The main message is that we are currently seeing the evolutionary breakdown of plant pollinators,” said Cheptou, an evolutionary ecologist at France’s National Center for Scientific Research and a professor at the University of Montpellier.
Resurrection plants
Using a method known as “resurrection ecology” to conduct the research, the study team germinated the seeds of four populations of wild field pansies, scientifically known as Viola arvensis, collected in the 1990s and early 2000s in the Paris region.
Some propagules, or parts of a plant that can be used to grow a new plant, can remain in the seed stage for “a very long time,” explained Acoca-Pidolle. They are living, but at a very low metabolic rate. “It’s like a long flight of stairs,” he said.
In 2021, the team found field pansies from the exact spot where the ancestral seeds were collected 20 to 30 years earlier. The scientists then performed a population genetic analysis that looked at rates of self-pollination and changes in heterozygosity, or genetic variability, as well as changes in flower traits related to pollinator attraction.
In a sample of 4,000 flowers, self-fertilization rates went from about 50% for the flowers collected two or three decades earlier to about 80% of their natural offspring, the authors found. Meanwhile, the “resurrected” flower surfaces were 10% larger, produced 20% more nectar and were attended by more bees than their modern counterparts.
‘Insurance policy’
An increase in pollinating or “self-pollinating” species of flowering plants is not always a bad thing, said Gretchen LeBuhn, a biology professor at San Francisco State University who studies pollinator-plant interactions.
“The way to think about (itself) is that it’s kind of like a retention strategy,” said LeBuhn, who was not involved in the study. Although increased selfing often leads to a decrease in genetic diversity in a population, among a number of other negative consequences, it can also maintain the population, she said. “Like an insurance policy.”
A reduction in genetic diversity within a plant population is important because those with a reservoir of genetic diversity can better respond to major environmental changes, effectively reducing the risk of extinction.
But when reading the new paper, part of her “really thought that an increase in identity means that the population is to be preserved,” LeBuhn said. “If plants can persist over time, with the number of pollinators increasing again, it would suggest that this is a species preservation mechanism.”
It is not clear whether that evolutionary change can be reversed, however – although the new research suggests that a depletion of the genetic diversity of plant populations is expected in the term, according to Acoca-Pidolle.
“Some scientists believe that there may be a tipping point beyond which a plant cannot go back,” he noted, adding that the evolutionary transition is classically considered “irreversible”. The next big question is to investigate whether these wild pansies are able to recover from the effects of self-harvesting, said Acoca-Pidolle.
Meanwhile, it’s important to acknowledge that the authors don’t have the details of what was happening to pollinators 20 to 30 years ago, LeBuhn said. “The one thing they can’t document is how different the pollinators were in these sites over time,” she said — which stems from gaps in extensive historical pollinator monitoring.
“(The study) is a really important demonstration of the tight connections between plant communities and pollinators,” LeBuhn said. “I think the next step in research is to understand the implications for pollinators.”
Humanity’s permanent footprint
Other recent studies have found that pollinator decline, a result of harmful human activities, threatens the future of food crops and the survival of the many species that depend on them.
The growing body of research strengthens the case for urgent conservation measures — such as developing and protecting flower-rich habitats that serve as flowering and nesting resources — to help with global pollinator decline, according to Acoca-Pidolle.
“Our impact is not just killing some individual plants … we are putting them on an evolutionary path that could be bad for them,” Acoca-Pidolle told CNN. “And even after we’re gone, for a long time, we’ll have traces of this evolutionary path of many species, of the biodiversity of the planet.”
Ayurella Corn-Muller He has reported for Axios and Climate Central. His book, “Devoured: The Extraordinary Story of Kudzu, the Vine That Ate the South,” is due out in the spring.
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