Genetic structure and gene flow in natural and managed forest tree populations of the interior spruce hybrid zone

White spruce (Picea glauca) is a widely distributed and economically important tree species in Canada. In the southwestern part of its range, it hybridizes extensively with Engelmann spruce (Picea engelmannii) creating enormous hybrid swarms in a great part of British Columbia. The pattern and process responsible for hybrid zone maintenance as well as the influence of introgression between species is poorly understood. Because of their similarity in morphology, they have been treated as a complex, known as interior spruce. Although geographical (elevational) and environmental (climatic) differentiation have been well studied through multiple long-term provenance trials, the genetic composition of this zone and the effect of artificial selection on the genomic composition of interior spruce have never been thoroughly assessed.

This project used a combination of microsatellite markers, single nucleotide polymorphisms, and phenotypic traits to assess the extent of introgression in interior spruce; the relationships between hybrid ancestry, population location (elevation and latitude), and climate; and the effects of selective breeding on hybrid ancestry. Most populations in the southern half of BC are heavily introgressed, with pure white spruce individuals being rare and only found at low elevations, and pure Engelmann spruce found only at very high elevations. The hybrid zone appears to be very old, perhaps tens of thousands of years, and has likely migrated north from the western United States since the last glacial maximum. Selective breeding has increased the proportion of ancestry of white spruce in all but very high elevation breeding populations, and this shift may pre-adapt breeding populations to climate warming.

Funding: NSERC Discovery Grant, University Graduate Fellowship, Forest Investment Account through Forest Genetics Council of BC

Primary participants: [ de la Torre | Aitken ]

For more information

A.R. De La Torre, D.R. Roberts, S.N. Aitken. 2014. Genome‐wide admixture and ecological niche modeling reveal the maintenance of species boundaries despite long history of interspecific gene flow.  Molecular Ecology 23 (8): 2046–2059. [Open access]

A.R. De La Torre, T. Wang, B. Jaquish, and S.N. Aitken. 2014. Adaptation and exogenous selection in a Picea glauca × Picea engelmannii hybrid zone: implications for forest management under climate change. New Phytologist 201: 687-699 [Open access]