Blooming Change: A Story of Adaption

By Harshina Brijlall

7 May 2020

An orange jewelweed “open” flower (Photo by Fritz Geller-Grimm, CC BY-SA 2.5)

An orange jewelweed “open” flower (Photo by Fritz Geller-Grimm, CC BY-SA 2.5)

Humans may be busy practicing social isolation for some time, but with spring in full swing, nature is embarking on a flurry of interactions.  Birds are busy breeding and nesting, while flowers are beginning to bloom, hoping to attract pollinators.  But climate change, habitat loss and other factors have led to a steady decline in pollinator populations.  And so, just as humans are making lifestyle changes to survive the pandemic, wildflowers may also have to adapt to survive a reduction in pollinator visits.

Professor Christina Caruso and graduate student Hazel Panique from the Department of Integrative Biology are evolutionary biologists interested in how wildflowers are responding to pollinator decline.  In a recent study published in the American Journal of Botany, they determined that Impatiens capensis, otherwise known as orange jewelweed, had two different responses to decreased pollinator visits. 

Orange jewelweed is an annual wildflower that produces two types of flowers. The first is a non-descript closed  or “cleistogamous” flower with no exposed reproductive parts. This type of flower relies on self-fertilization to reproduce. The second type of flower is one that is much more familiar to us:  bright, attractive and fragrant. These “chasmogamous” flowers have open petals to encourage pollinator visits and cross-fertilization.

Both types of flowers have certain advantages and disadvantages. For example, closed flowers ensure the plant can reproduce even if pollinators are not present.  In contrast, open flowers allow for cross-pollination between plants, which increases genetic diversity and offspring vigour.  Caruso and Panique wanted to know if the presence of fewer pollinators would favour the production of one type of flower over another.  In other words, would a plant rely more heavily on self-fertilization and produce more closed flowers?  Or would it try to become more attractive to pollinators by producing showier and/or more open flowers?

The pair devised an unusual experiment that involved transplanting hundreds of pre-flowering jewelweed plants from a local nature trail to a study site at the University of Guelph’s Arboretum.  Half of the plants were left exposed to regular or “ambient” pollination, while the other half of plants were covered in netting every other day during flowering, which reduced pollinator visits by 50%.  Within just one season, the scientists were able to measure natural selection on the plants caused by a decrease in pollinators.

Caruso and Panique discovered that fewer pollinator visits resulted in a greater number of closed flowers. Somewhat surprisingly, however, it also led to the production of open flowers that were larger in size – which they believe was an effort by the plant to help draw in scarce pollinators.

This is double-edged response is good news for pollinators, says Caruso.  “There would be grave consequences for pollinators if wildflowers were to completely turn to selfing and produce only closed cleistogamous flowers, as many pollinators rely on the nectar and pollen that wildflowers provide. The world would also look a lot greyer as plants would not produce big, showy flowers to attract pollinators.”

Caruso’s lab will continue to study wildflower evolution as a result of human-driven global change, but will expand their work to include other plant species.  Fortunately, other plants should prove easier to work with. Orange jewelweed uses ballistic seed dispersal, which means the fruit springs open and forcefully expels its seed. This made it rather difficult for the researchers to collect seeds to measure the plant’s overall reproduction.

Caruso praises Panique for her herculean efforts in working with a challenging study species like orange jewelweed. “She did a heroic job of seeing the project through and collecting the seeds before their flying launch."  

Many studies focus on the role of pollinators in agricultural production, but Caruso points out that pollinators such as bees, moths, and butterflies rely on multiple sources of nutrition, including wildflower populations.

"We need to remember that all species are linked and there is more to pollinators and pollination than just honeybees and agricultural crops,” says Caruso.   

The study adds a complex but important layer to our understanding of how human impacts on the environment are affecting the evolution of wild species.


This research was funded by the Natural Sciences and Engineering Research Council.


Read the full study in the journal American Journal of Botany

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