New study finds plants evolve to beat biological clock

Researchers at York University and the University of Toronto have uncovered genetic evidence that plants are capable of evolving at a rapid pace when nature’s reproductive clock is ticking.

In a new study published in Proceedings of the National Academy of Sciences, researchers detail their sequencing of 39 nuclear genes from specimens of Capsella rubella – commonly known as pink shepherd’s purse – and its genetic predecessor, Capsella grandiflora. They estimate the species developed the ability to fertilize itself within the past 20,000 years.

Right: Capsella bursa-pastoris is a close relative of Capsella rubella

Previously, little had been known about the speed at which plants shift from outcrossing (the practice of introducing unrelated genetic material into a breeding line) to self-fertilization.

“We were surprised as to the time period over which this speciation event seems to have occurred. In terms of evolutionary time, 20,000 years ago is extremely recent,” says the study’s lead author, John Paul Foxe, a PhD candidate in York’s Department of Biology.

“By contrast, a speciation event between two species of Arabidopsis, a close relative of Capsella, is estimated to have occurred somewhere between five and eight million years ago,” he notes.

Scientists theorize that plants undertake this process in a trade-off between the benefits of greater self-reliance and the disadvantages inherent in inbreeding.

The study hypothesizes that Capsella’s reproductive abilities evolved in response to a major environmental shift following the last ice age. This environmental extreme persisted for several thousand years, followed by agriculture spreading across Europe, producing new habitats that would have been favourable to plants more capable of colonization.

As a result, Capsella reached a near-complete population bottleneck causing major reduction in population size.

“One of the advantages of self-fertilization is the ability to colonize new habitats from a very small foundling population, and that’s precisely what we saw with Capsella,” Foxe says.

The research was conducted at York and the University of Toronto and supervised by Stephen Wright, a professor in York’s Graduate Program in Biology and assistant professor in the Department of Ecology & Evolutionary Biology at U of T.

The study, “Recent speciation associated with the evolution of selfing in Capsella”, was published on Feb. 19. It is co-authored by Tanja Slotte, University of Toronto; Eli A. Stahl, University of Massachusetts, Dartmouth; Barbara Neufferand Herbert Hurka, Universität Osnabrück, Germany;  and Wright.

To download a copy of the study, click here.