Parisian pansies are smaller, produce less nectar than 20-30 years ago; environmental changes can to further decline in pollinators, warn scientists
Viola arvensis or field pansies. Photo: iStock In the first evidence of rapid evolution, scientists have discovered a flower growing in Paris, France is producing less nectar and smaller flowers to attract fewer pollinators.
The scientists also found evidence that the plant field pansy, scientifically known as Viola arvensis, is self-pollinating, as indicated the research. Ongoing convergent evolution of a selfing syndrome threatens plant pollinator interactions, said the paper published in journal New Phytologist.
The study found that flowers of the wild pansy variety grown in four locations in Paris produced 20 per cent less nectar and were 10 per cent smaller. The scientists compared the growth of the flowers grown in the same fields with seeds from 20-30 years ago. Insects also frequented the fields where the flowers grew.
Scientists discovered that the plant evolved to self-pollinate in order to attract fewer pollinators due to the decreasing availability of insects.
“This study is the first to show convergent evolution across populations, reduced rewarding trait and reduced attractiveness,” the research paper said.
Self-pollination is the process by which plants reproduce themselves. The behaviour is contrary to the convention of angiosperms, which rely on insects to pollinate in order to reproduce — an interconnected relationship in nature.
Plants produce nectar to attract insects, which collect nectar for food and transport pollen between plants in nature. The interlinked give-and-take relationship has evolved over 100 million years of coevolution, the study noted.
The researchers used the “resurrection ecology” method, wherein they planted seeds from the 1990s and 2000s, which were 20-30 years old, against their contemporary descendants from 2021. The seeds were planted in four locations across Paris, growing about 4,000 plants.
The researchers took advantage of, “An ancestral seed collection of the field pansy (Viola arvensis) collected about two decades ago in the Paris region (France) to test whether this species' mating system has evolved in response to recent pollinator declines.”
It means that the plants that have incorporated behaviour over millions of years are showing rapid evolution over 50 years.
“Population genetics analysis reveals a 27 per cent increase in realised selfing rates in the field during this period. We documented trait evolution towards smaller and less conspicuous corollas, reduced nectar production and reduced attractiveness to bumblebees, with these trait shifts convergent across the four studied populations,” the researchers noted.
Apart from a decrease in nectar and flower size, the study revealed no change in leaf size or other physiological changes.
In another research, a contemporary evolution of plant reproductive strategies under global change was revealed by stored seeds. Scientists found that field pansies depending on self-pollination increased by 25 per cent in 20 years.
Pierre-Olivier Cheptou is a co-author of both studies.
Scientists warned that the move may benefit plants in the short term but may threaten their existence owing to climate change and other environmental changes.
“While angiosperm–pollinator interactions have evolved over the long term, our study shows that current environmental changes can drive a rapid evolution towards a breakdown of such interactions,” it stated.
Further, pansy species and pollinators may enter a loop where plants producing less nectar enable less food availability, driving them towards declines.
“Evolution towards selfing could thus be driven by natural selection over the short term but could impede long-term plant population survival,” it noted, adding that the environmental changes can lead to double jeopardy among pollinators as they become victims of the change in addition to plant trait evolution.
However, “This, in turn, may result in an eco-evolutionary-positive feedback loop that furthers pollinator declines, further reinforcing plant evolution towards a selfing syndrome,” the researchers said, adding that this explains the plant-pollinator network degradation that they observed in earlier studies.
The study pressed on an urgent need to analyse if these results are symptomatic or are seen among a broader behavioural change in the relationship between angiosperms and their pollinators.
“If so, understanding whether there is a possibility to reverse this process and break this eco-evolutionary-positive feedback loop,” the study observed.
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