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An ancient, interdependent relationship that contributes to food systems and ecosystem stability around the world may be changing.
Many flowering plants can self-pollinate or transfer pollen between their own flowers for seed production and propagation, but most of these plants have relied on pollinators such as butterflies and bees to reproduce.
Now—amid reported declines in many pollinator populations—a new study into the evolution of one floral species’ mating system has revealed a remarkable shift that could worsen the challenges faced by plants’ insect partners.
The reproductive evolution of flowers may be linked to environmental changes, such as habitat destruction and ongoing rapid declines in pollinator biodiversity, according to Samson Acoca-Pidolle, who led the study published Dec. 19 in the journal New Phytologist.
Comparing wild violet seeds collected in France decades ago with the plants’ modern descendants, Acoca-Pidolle and colleagues found that today’s flowers are smaller and produce less nectar as a result of increased self-pollination, which has a direct impact on pollinator behavior. . According to the study, violets of the past were less self-pollinating and attracted many more pollinators than those of today.
“It seems that only traits involved in the plant-pollinator interaction evolve,” said Acoca-Pidolle, a doctoral researcher at the University of Montpellier. Changes could restrict the ability of plants to adapt to future environmental changes and have consequences for “whole floral biodiversity”; could potentially lead to reduced genetic, species and ecosystem diversity of flowering plants.
“This could increase the decline of pollinators and cause a vicious feedback loop,” study co-author Pierre-Olivier Cheptou told CNN. If plants produce less nectar, there will be less food available to pollinators, accelerating the rate of decline in animal numbers.
“The main message is that we are now seeing the evolutionary collapse of plant pollinators in the wild,” said Cheptou, an evolutionary ecologist at the French National Center for Scientific Research and a professor at the University of Montpellier.
resurrected plants
Using a method called “resurrection ecology” to conduct the research, the study team germinated the seeds of four populations of wild violets, scientifically known as Viola arvensis, collected from the Paris area in the 1990s and early 2000s.
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,” Acoca-Pidolle explained. They are alive, but their metabolic rate is very low. “It’s like a long sleep,” he said.
In 2021, the team sourced the field violets from the same place where the ancestral seeds were collected 20 to 30 years ago. The scientists then conducted a population genetic analysis looking at self-pollination rates and changes in heterozygosity, or genetic variability, as well as changes in flower traits associated with pollinator attractiveness.
In a sample of 4,000 flowers, the authors found that self-pollination rates increased from about 50% for flowers collected two to three decades ago to roughly 80% for their naturally occurring descendants. Meanwhile, the “resurrected” flowers had surfaces that were 10% larger than their modern counterparts, produced 20% more nectar, and were frequented by more bumblebees.
‘An insurance policy’
Increased self-pollination, or “self-pollination,” of flowering plant species isn’t always a bad thing, said Gretchen LeBuhn, a biology professor at San Francisco State University who studies interactions between pollinators and plants.
“The way you think about yourself is kind of like a holding strategy,” said LeBuhn, who was not involved in the research. He added that although selfing often leads to a decrease in genetic diversity in a population, among many other negative consequences, it can also maintain the population. “It’s like an insurance policy.”
Reducing genetic diversity within a plant population is important because those with a reservoir of genetic diversity can better respond to major environmental changes and effectively reduce the risk of extinction.
But LeBuhn said that while reading the new paper, some “thought that the increase in self-establishment meant that the population would be maintained.” “If plants can persist over time and pollinator populations increase again, this could be said to be a mechanism for species conservation.”
However, it is unclear whether this evolutionary change can be reversed; However, the new research suggests that there is an expectation of a decrease in the genetic diversity of the plant population by the end of the period, according to Acoca-Pidolle.
“Some scientists believe there may be a tipping point from which a plant cannot return,” he said, adding that the evolutionary transition was classically considered “irreversible.” Investigating whether these wild pansies have the ability to escape the effects of self-propagation is the next big question, Acoca-Pidolle said.
Meanwhile, it’s important to acknowledge that the authors don’t really have data on what was happening with pollinators 20 to 30 years ago, LeBuhn said. “The only thing they can’t document is the magnitude of the difference between pollinators in these areas then and now,” he said; This is due to gaps in historically widespread pollinator monitoring.
“(The study) is a really important demonstration of the tight connections between plant and pollinator communities,” LeBuhn said. “I think the next step in the research is to understand what the effects are for pollinators.”
Humanity’s permanent footprint
Other recent research has found that declining pollinator populations, a result of harmful human activities, threaten the future of food crops and the survival of many species that depend on them.
According to Acoca-Pidolle, growing research supports the need for urgent conservation measures, such as developing and protecting flower-rich habitats that serve as flower and nesting resources, to help stem the decline of global pollinators.
“Our impact is not just killing some plants, we’re putting them on an evolutionary path that could be bad for them,” Acoca-Pidolle told CNN. “And even after we disappear, we will have a footprint on the evolutionary trajectory of many species and the planet’s biodiversity for a long time.”
Ayurella Horn-Muller He has reported for Axios and Climate Central. His book, “Devourer of Devourer: The Extraordinary Story of the Kudzu Vine that Devoured the South,” will be released in the spring.
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