The emerging discipline of community genetics/genomics has demonstrated heritable variation in communities of organisms (e.g., insects, microbes) that are associated with individual genotypes of foundation plant species. The particular plant genes, or gene regions, underlying those associations, however, are largely unknown. Trembling aspen (Populus tremuloides) is a foundation forest species with extraordinary genotypic variation that, via phytochemical and related traits, governs interactions of aspen with canopy herbivore and soil microbial communities. We established WisAsp (Wisconsin Aspen), a genetic mapping garden of P. tremuloides, to provide an experimental platform for identifying genomic components of aspen that explain heritable variation in associated communities. Approximately 500 genotypes, collected along a 375 km north-south transect in Wisconsin, were planted with replication into a common garden near Madison, Wisconsin in 2010. Since then we have monitored tree growth, phenology, and foliar chemistry, and in recent years we have censused insect communities. Sequence capture genotyping of the full WisAsp population is currently underway using 60,000 probes (1-2 probes per gene), with ~180,000 examined single nucleotide polymorphisms (SNPs) predicted.
Here, we summarize initial findings of genotypic variation at WisAsp, and promote the availability of this resource to the scientific community. After several years of growth, tree size varied by 55-fold among aspen genotypes. Budbreak phenology varied by a month across genotypes. Levels of phenolic glycosides, key determinants of interactions with folivorous insects, varied by 10-25-fold. Levels of condensed tannins, which mediate interactions with soil microbes, varied by 24-fold. Densities of extrafloral nectaries varied by 27-fold. Finally, densities of herbivorous insects varied by several orders of magnitude. These and related phenotypic data will be coupled with detailed genomic data to conduct genome-wide association (GWA) studies. Early findings suggest that WisAsp will provide a powerful platform for pursuit of community genetics research in a forest tree species.