If you look at the trees as you're driving on the Trans-Canada Highway toward Banff National Park, you will see Engleman spruce on the cooler, wetter northeast-facing slopes of the Three Sisters. Across the valley, on the warmer, drier southwest-facing slopes of Grotto Mountain, are white spruce.
The species typically crossbreed in central British Columbia and Northern Alberta, but those in the Bow Valley corridor west of Calgary remain distinct species because they are strongly adapted to different sides of the same valley.
Scientists at the University of Calgary who studied the two types of trees have determined that they use the same genetic tool kit whether they grow in the mountains or across vast northern latitudes.
"It's pretty remarkable seeing how similar the patterns in their genomes look," says Dr. Sam Yeaman, PhD, professor with the Department of Biological Sciences in the Faculty of Science. "I was expecting there to be some degree of similarity, but the degree of similarity was pretty striking."
The research, which was published earlier this spring in the journal Molecular Biology and Evolution, is important because it helps scientists understand how species survive and evolve. The information will allow foresters to study drought tolerance and may eventually help to develop markers to improve tolerance in tree-breeding programs.
The study suggests that there's a consistent and even predictable pattern of local adaptation across geographical landscapes, with some regions of the genome being favoured across both species. This strong and repeated natural selection is presumably mainly driven by climate, as Engelmann spruce tends to live in higher elevation montane regions with deeper snowpacks and warmer average temperatures, while white spruce inhabits colder, drier and lower-elevation boreal regions.
Yeaman, who's corresponding author on the paper led by postdoctoral researcher Dr. Gabriele Nocchi, PhD, says the research team spent many days hiking in the Canadian Rockies west of Calgary, to gather 384 samples from the trees that could then be studied in his lab.
Yeaman says it's a bit like having a natural laboratory in the mountains.
"Each valley is like its own little lab setting to see how evolution has played out," he says. "These species colonized these valleys presumably independently, so, if we see the same patterns pop up over and over again in each valley, that really strongly suggests certain regions of the genome being particularly important."
The results, Yeaman adds, also provide insight into evolution.
"Our lab does a lot of work on testing evolutionary theory, just understanding the process of evolution at a basic level," he says. "By looking at places where adaptation is repeated in nature, that allows us to get more insight into how evolution works.
"What was fascinating for us was to see that the same patterns that were present across thousands of kilometres were seen in these small spatial scales."
Yeaman says they will continue sampling the other valleys to gain more insight into the traits that drive adaptation.
