Journal Article

Continental-scale assessment of genetic diversity and population structure in quaking aspen (Populus tremuloides)

Callahan, Colin M., Madritch, Michael D., Mock, Karen E., Rowe, Carol A., Shaw, John D., Ryel, Ronald J.

2013

Overview

Aim Quaking aspen (Populus tremuloides) has the largest natural distribution of any tree native to North America. The primary objectives of this study were to characterize range-wide genetic diversity and genetic structuring in quaking aspen, and to assess the influence of glacial history and rear-edge dynamics. Location North America. Methods Using a sample set representing the full longitudinal and latitudinal extent of the species' distribution, we examined geographical patterns of genetic diversity and structuring using 8 nuclear microsatellite loci in 794 individuals from 30 sampling sites. Results Two major genetic clusters were identified across the range: a south-western cluster and a northern cluster. The south-western cluster, which included two subclusters, was bounded approximately by the Continental Divide to the east and the southern extent of the ice sheet at the Last Glacial Maximum to the north. Subclusters were not detected in the northern cluster, despite its continent-wide distribution. Genetic distance was significantly correlated with geographical distance in the south-western but not the northern cluster, and allelic richness was significantly lower in south-western sampling sites compared with northern sampling sites. Population structuring was low overall, but elevated in the south-western cluster. Main conclusions Aspen populations in the south-western portion of the range are consistent with expectations for a historically stable edge, with low within-population diversity, significant geographical population structuring, and little evidence of northward expansion. Structuring within the south-western cluster may result from distinct gene pools separated during the Pleistocene and reunited following glacial retreat, similar to patterns found in other forest tree species in the western USA. In aspen, populations in the south-western portion of the species range are thought to be at particularly high risk of mortality with climate change. Our findings suggest that these same populations may be disproportionately valuable in terms of both evolutionary potential and conservation value.

• Publisher: Blackwell Publishing Ltd,John Wiley & Sons Ltd,Blackwell,Wiley Subscription Services, Inc
• Subject: Animal and plant ecology / Animal, plant and microbial ecology / Aspen / Biogeography / Biological and medical sciences / Biological evolution / climate / Climate change / Diversity: historical and climatic imprints / Ecological genetics / Forest ecology / Fundamental and applied biological sciences. Psychology / General aspects / genetic / Genetic diversity / Genetics / Genetics of eukaryotes. Biological and molecular evolution / Last Glacial Maximum / Microsatellites / Mortality risk / North America / phylogeography / Plant ecology / Plant species / Pleistocene / Population / Population ecology / Population genetics / Population structure / Populus tremuloides / rear edge / Synecology / tree / western USA