Rhododendron flower species lead a “blooming calendar”

Evolution’s unofficial tagline of “survival of the fittest” may conjure up grim images of animals fighting for scarce resources and adapting to best thrive in a changing and scary world where there’s no tomorrow guaranteed. But sometimes evolution can be kind and even a little cooperative. While animals like the amazing Galapagos Island tortoises and finches are usually the stars of evolutionary tales, some scientists are studying the plant world to better understand the process.

A study published today in Journal of Ecology seeks to solve a floral evolutionary mystery in China. The grasslands of the Hengduan Mountains in southwest China are next to the Qinghai-Tibetan Plateau. Scientists consider the area a biodiversity hotspot, or an ecologically fragile place with an unusually high number of different species. Here dozens of species of closely related plants seem to live in harmony.

Rhododendrons are a genus of flowering shrubs that include bright purple and pink azaleas, trumpet-shaped elviira, and blue petrel. In the Hengduan Mountains, “they form thickets on the sides of the mountains, it looks like an ocean of flowers,” Chin Li, a postdoctoral researcher at the Field Museum and lead author of the paper, said in a press release.

A process called speciation is responsible for the diversity among rhododendrons here. Speciation occurs when a new species emerges from a common ancestor. The newly diverged species are expected to be much more ecologically similar than the more distant plants, according to Rick Rhee, curator at Chicago’s Field Museum and senior author of the study.

“There’s this basic idea in niche ecology that the lifestyle of a species, like what it eats and how it fits into its environment, can’t be replicated in the same community. If two species with the same lifestyle live in the same space, they will compete with each other, so either one or both of them will adapt to different, non-overlapping lifestyles, or they will go extinct,” Rhee said. in a press release. “Because there are so many closely related rhododendron species living together in these mountains, we wanted to understand how they can coexist.”

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To resolve this case, the team studied the flowering patterns of 34 rhododendron species. As if the plants had a common calendar, the team found that they burst into bloom at different times of the season so that they don’t have to compete for the attention of pollinators.

What is puzzling about the unique genus of flowers is that the closely related rhododendrons here should be even more likely to be locked in a battle for resources, but there are many ways for them to adapt to coexist. “They can become very different in terms of their preferences for soil, light and moisture, very basic physiological functional traits. They may also evolve differences to reduce this potential for cross-pollination or competition for pollinators. This will manifest itself through differences in flower shape, size or color, or it may manifest itself when they make their flowers available to pollinators,” Rhee said. “By separating that timeline, they can reduce their chances of wasting their pollen and the resources that go into reproduction.”

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According to the study, these evolutionary strategies help explain why rhododendrons have not driven each other to extinction over time.

“Going in, we had a hunch the timing would be important, but we weren’t too sure,” Rhee said in the release. “Obviously there is a long season to see flowers in the Himalayan region – there are some species that put on striking blooms against a snowfield, and others wait until the end of summer. Our data analysis confirms this suspicion.

Confirming the timing of the flowering schedule will also be key to better understanding the threat these plants face from climate change. According to Rhee, there is evidence that climate change is affecting flowering times, causing declines and extinctions.

“The question is, how will plant communities around the world respond?” Weather is part of what signals them to bloom, and as climate change affects weather, it is likely to alter this competitive landscape,” Rhee said in the release. “When the environment changes, species have three choices: move, adapt, or die. Climate change is accelerating this dynamic.”

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