Data from: Genome-wide sequence-based genotyping supports a nonhybrid origin of Castanea alabamensis

The genus Castanea in North America contains multiple tree and shrub taxa
of conservation concern. The two species within the group, American
chestnut (Castanea dentata) and chinquapin (C. pumila sensu lato), display
remarkable morphological diversity across their distributions in the
eastern United States and southern Ontario. Previous investigators have
hypothesized that hybridization between C. dentata and C. pumila has
played an important role in generating morphological variation in wild
populations. A putative hybrid taxon, Castanea alabamensis, was identified
in northern Alabama in the early 20th century; however, the question of
its hybridity has been unresolved. We tested the hypothesized hybrid
origin of C. alabamensis using genome-wide sequence-based genotyping of C.
alabamensis, all currently recognized North American Castanea taxa, and
two Asian Castanea species at >100,000 single-nucleotide
polymorphism (SNP) loci. With these data, we generated a high-resolution
phylogeny, tested for admixture among taxa, and analyzed population
genetic structure of the study taxa. Bayesian clustering and principal
components analysis provided no evidence of admixture between C. dentata
and C. pumila in C. alabamensis genomes. Phylogenetic analysis of
genome-wide SNP data indicated that C. alabamensis forms a distinct group
within C. pumila sensu lato. Our results are consistent with the model of
a nonhybrid origin for C. alabamensis. Our finding of C. alabamensis as a
genetically and morphologically distinct group within the North American
chinquapin complex provides further impetus for the study and conservation
of the North American Castanea species.