Old plant populations offer new clues to climate resilience

When scientists think about how plants will respond to climate change, they often look north. As temperatures rise, many species are expected to shift their ranges toward cooler regions with a loss of populations in warmer habitats. But new research from the University of Virginia, published in the journal Evolution Letters, suggests the story may be more complicated and more hopeful.

The University of Virginia’s Commonwealth Professor of Biology Laura Galloway and postdoctoral research associate Antoine Perrier are studying what they call “rear-edge” populations, those found at the warmest edges of their geographic ranges. These populations, often descended from groups that survived the last ice age, have endured thousands of years of climate change.

“Because these populations have been there since the last glaciation, they’ve gone through warming in the past,” Galloway said. “We can use them as models for what we might expect in response to future warming.”

Their recent work on a native wildflower brings together multiple lines of evidence, including genomics, greenhouse experiments and field studies, to test how these populations evolved and what that might mean for the future.

Rethinking Vulnerability at the Warm Edge

Conventional ecological models predict that populations at the warm edge of a species’ range will be the first to disappear as temperatures rise. But Perrier and Galloway found something different.

“We often think that populations at the warmer edge are the ones that will go extinct,” Perrier said. “But it turns out there’s a lot that we don’t know about these populations.”

One possibility is that they harbor high genetic diversity, a legacy of their age and persistence since the last ice age, and therefore may be a resource for adapting to future change. Another is that as small, isolated populations, they might show signs of genetic drift, a process that reduces diversity and can make populations more fragile. A third possibility is that these populations have undergone local adaptation, evolving traits that allow them to thrive in conditions warmer than typical for the species.

The answer, in this case, was clear.

“We found patterns of local adaptation throughout the range,” Perrier said. “But what was very interesting is that in the deep south only the populations coming from very similar environments were able to actually grow and reproduce.”

In other words, southern populations have evolved specific traits that allow them to survive and reproduce in warmer climates. Northern populations transplanted into those same conditions failed to flower at all.

A Surprising Forecast for Climate Change

The findings challenge a central assumption about how species will respond to warming. Instead of southern populations disappearing first, the researchers’ data suggest that they are likely to persist, while populations in the middle of the range may struggle.

Many plant species use cold to cue reproduction, “As winters get warmer, populations are expected to experience a loss in reproduction,” Perrier said. “But this was not the case for the rear edge.”

Southern populations may be less affected by continued warming because they have already evolved to reproduce without relying on cold winter cues. By contrast, populations in regions like the mid-Atlantic could face new challenges.

“It’s almost the opposite of what we expect,” Galloway said, noting that both far-northern and far-southern populations may prove more resilient than those in between.

The work also points to practical applications. Traits that allow southern populations to thrive in warmer climates could potentially be introduced into more vulnerable populations through conservation strategies such as assisted gene flow.

Natural Laboratories for the Future

Beyond its immediate findings, the research highlights the value of studying long-term evolutionary history. Rear-edge populations, the researchers argue, act as “natural laboratories” for understanding how species respond to environmental change.

For Perrier, the work underscores both the urgency and the opportunity of climate research.

“We don’t often think of these populations as being the ones that might be the best adapted to future conditions,” he said. “But they could actually persist and change how we think about species responses to climate change.”