EDITOR'S CHOICE IN EVOLUTION
S. Yeaman et al., “Convergent local adaptation to climate in distantly related conifers,” Science, 353:1431-33, 2016.
Related species sometimes adapt to similar environments with mutations in the same genes. But convergent evolution is usually observed in species that recently diverged or in traits that involve only a few genes and therefore may have fewer possible evolutionary paths. New research from the snowy North tells a different story.
Interior spruces (Picea glauca and P. engelmannii) and lodgepole pine (Pinus contorta) each have hundreds of genes that contribute to one outcome: surviving the brutal winters of Canada and the northern U.S. “You would think that there would be many ways to get the same phenotype” with so many genes involved, says Sally Aitken, a population geneticist at the University of British Columbia. And yet, the two conifer groups share 10 percent to 18 percent of their cold-adaptation genes, Aitken and her colleagues report in a recent study.
These species diverged when the Earth’s climate was warmer, around 140 million years ago—leaving plenty of time to evolve unique genes. Although different variants of those genes arose in each species, evolution appears to have put them to use in the same way. The study suggests evolution “is repeatable even though these trees diverged so, so long ago,” says Patrik Nosil, an evolutionary biologist at the University of Sheffield in the U.K.
Frozen in Time
One possible explanation, Aitken says, is that the strong selective pressure of the climate constrained the emergence of new genes, forcing these species to rely on variants of old genes.