Very bad news for nature lovers – and nature.
Flowers could become smaller and less attractive as they evolve to become self-pollinating due to a decline in insects, a new study claims.
The shock findings come from researchers in France who found some plants are showing reductions in floral displays and nectar production.
They conclude this is because they are evolving to rely less and less on bees due to rapidly depleting populations.
But scientists warn that changing in this way to survive could also prove to be the plants’ downfall – and eventually lead to their extinction.
French scientists investigating recent evolutionary changes in flowers compared field pansies growing in Paris now to those from 20 and 30 years ago.
They found that today’s flowers grow smaller, produce less nectar and are less frequently visited by pollinators than their ancestors.
The researchers warned that the trend constituted a ‘vicious circle’ in which increased reliance on self-fertilisation could lead to reduced nectar for pollinating insects – in turn exacerbating their decline.
Scientists from the French National Centre for Scientific Research (CNRS) and the University of Montpellier teamed up to assess the impacts of population decline in pollinating insects such as bees on plant populations.
These declines are blamed on environmental changes such as habitat destruction and fragmentation, agricultural land pollution and the introduction of other species.
A recent study in Germany found that more than three-quarters of the biomass of flying insects have vanished from protected areas in the last 30 years.
These shifts in the mating systems of plants and flowers lead to higher ‘selfing’, or self-pollination – where the plant fertilises itself with its own pollen to reproduce.
However, few plants self-pollinate without the aid of pollen vectors such as the wind or insects.
And when selfing, plants become less focused on appearing attractive to pollinators with enticing floral displays.
The French research team used an ancestral seed collection of the Parisian field pansy – Viola arvensis – to test whether the species’ mating system had evolved in response to recent pollinator declines.
They compared these ancestors, collected in the 1990s to the early 2000s, with their modern descendants, collected in 2021.
The researchers measured the traits of a total of 4,000 plants, including the length of their petals on the five first-opened flowers on the main stem of each plant.
They also performed ‘pollinator preference’ experiments involving bumblebees.
The team behind the study, published in the journal New Phytologist, found a consistent average decrease of 20% in the traits of the plants used to attract pollinators, represented by decreases in nectar volume.
Today’s flowers were also found to be 10% smaller and far less visited by pollinators than their ancestors.
The researchers said this provided strong evidence of the relationship between pollinators and plants deteriorating.
They added that this evolutionary transition is widely considered to be ‘irreversible’, and could eventually lead to the extinction of plant species.
‘Evolution towards selfing could be driven by natural selection over the short term but could impede long-term plant population survival,’ said lead author Pierre-Olivier Cheptou, a researcher from CNRS.
‘We documented trait evolution towards smaller and less conspicuous [petals], reduced nectar production and reduced attractiveness to bumblebees.
“If this rapid transition towards a selfing syndrome reflects a broader trend among [flowering plants], it may reflect a concerning extinction debt.’
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