Tree Genetics & Genomes

, Volume 9, Issue 3, pp 669–681 | Cite as

Population genetic structure of Picea engelmannii, P. glauca and their previously unrecognized hybrids in the central Rocky Mountains

Original Paper


Areas of geographic overlap between potentially hybridizing species provide the opportunity to study interspecific gene flow and reproductive barriers. Here we identified hybrids between Picea engelmannii and P. glauca by their genetic composition at 17 microsatellite markers, and determined the broad-scale geographic distribution of hybrids in the central Rocky Mountains of North America, a geographic region where hybrids and isolation between species had not previously been studied. Parameter estimates from admixture models revealed considerable variation in ancestry within and among collection sites, suggesting that within this area of geographic overlap, the interaction of the two species varies extensively. The results document a previously unrecognized patchy distribution of hybrids between P. engelmannii and P. glauca, including locations where hybrids were not known or expected to exist. Further, the ancestry of many hybrids was consistent with multiple generations of hybridization, with probable directional backcrossing to P. engelmannii, suggesting a relatively porous species boundary. The identification and characterization of hybridization between these spruce in this region raises the question of what factors maintain barriers to gene flow in these long-lived forest trees. The current research lays the groundwork for future study of the ecological and evolutionary contexts of their hybridization, as well as of differential introgression and permeability of species boundaries.


Admixture Geographic overlap Hybridization Spruce Picea 



The authors thank P. Haselhorst for assisting in the field, C. Wilcox (Coronado National Forest), P. Stankowski and W. Parker (Lakehead University, Ontario, Canada), D. Wolf and N. Takebayashi (University of Alaska–Fairbanks) for collecting needles from parental populations, Z. Gompert for assistance with statistical analyses, the Buerkle lab, three anonymous reviewers and Associate Editor S. Aitken for valuable comments on the manuscript, and the Nevada Genomics Center at the University of Nevada for providing high quality and rapid genotyping services. This research was funded by the Wyoming Native Plant Society, John W. Marr Memorial Fund, Shoshone National Forest, H. T. Northen Summer Fellowship in Botany, and UW-NPS Research Center.

Supplementary material

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© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Department of Botany & Program in EcologyUniversity of WyomingLaramieUSA

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