Researchers at McGill University and the United States Forest Service have found that plants living in areas where human activity has caused population crashes carry long-lasting genetic traces of that history, such as reduced genetic diversity. Because genetic diversity helps species adapt to climate change, disease and other stresses, the study suggests it is vital to consider a population's history-influenced genetics alongside its size and habitat in conservation planning.
"Two populations may look equally healthy on the surface, yet one may be far more vulnerable to future environmental change because it lacks genetic diversity and consists of individuals with poorly mixed genetic material. This can impede evolutionary responses to changing conditions," said Daniel Schoen , study co-author and W.C. Macdonald Professor of Botany in McGill's Department of Biology .
"Our findings suggest that in fragmented landscapes, conservation decisions based only on population size or habitat area may miss hidden genetic risks, especially in plant species that have the capacity to found populations through self-pollination," he said.
What DNA can reveal about a population's past
While past research has shown that human‑caused habitat fragmentation can harm plant populations, this study examined how they respond over time, including their prospects for resilience.
The researchers studied the population genetics of Impatiens capensis (jewelweed), a common plant native to North America, drawing samples from small, isolated patches surrounded by agriculture and urban land. Although the plant is not endangered, researchers said they chose it because it can establish populations through self-pollination.
The team created a reference genome, or a kind of genetic blueprint, using plants from different jewelweed patches in floodplain forests and wetlands in Wisconsin. Then they used the reference genome to reconstruct each population's history through demographic modelling. By examining how common different genetic variants were within each population, they could trace periods of growth, decline and recovery.
The researchers found sharp differences in genetic makeup depending on the population's past, whether it was founded by only a few individuals or was rebuilding after disturbances such as flooding. Populations that experienced fewer severe population crashes ("bottlenecks"), or that had more time to recover, retained higher genetic diversity, lower inbreeding levels and genomes that had been more thoroughly reshuffled by recombination. In contrast, populations that went through more severe bottlenecks and those that had less time to recover showed reduced diversity, higher inbreeding levels and genomes that were less recombined.
"Think of each genome as a 52-card deck: populations with fewer effective shuffles retain longer runs of cards in the same order, whereas those with more time and larger population sizes experience more cumulative shuffling," Schoen explained. "In populations with fewer recombined genomes, adaptation is reduced because beneficial variants are more often trapped within large blocks of linked DNA rather than being freely combined and selected independently.
"These differences persist for many generations and cannot be explained by present-day population size alone," he said.
Toward improved conservation
Researchers in Schoen's lab and McGill Professor Anna Hargreaves 's lab are now focusing on a rare plant species, Lupinus perennis (Sundial Lupine), which may be at risk or declining in Canada. The plant also serves as a host for the endangered Karner blue butterfly.
Schoen said information gathered through this type of study can help guide decisions about land use, habitat restoration and broader conservation efforts.
About this study
" Population genomic signatures of founding events in autonomously self-fertilising plants: A test with Impatiens capensis ," by Daniel Schoen and Rachel Toczydlowski, was published in New Phytologist.
The research was funded in part by the Natural Sciences and Engineering Research Council of Canada and the U.S. Department of Agriculture, Forest Service.
