Diversification, Spread, and Admixture of Octoploid Strawberry in the Western Hemisphere

Abstract

Premise of the study: Octoploid strawberry (Fragaria sp.) has a complex evolutionary history that has until recently been intractable due to limitations of available genomic resources. While recent work has further uncovered the evolutionary history of the octoploid strawberry, there are still open questions. Much is still unknown about the evolutionary relationship of the wild octoploid species, Fragaria virginiana and Fragaria chiloensis, and gene flow within and among species after the original formation of the octoploid genome. Methods: We leveraged a diversity collection of wild octoploid ecotypes of strawberry representing the recognized subspecies and ranging from Alaska to Southern Chile, and a high density SNP array to investigate wild octoploid strawberry evolution. Evolutionary relationships are interrogated with phylogenetic analysis and genetic clustering algorithms. Additionally, admixture among and within species is assessed with model-based and tree-based approaches. Key Results: Phylogenetic analysis revealed that the two octoploid strawberry species are monophyletic sister lineages. The genetic clustering results show substructure between North Americana and South American F. chiloensis populations. Additionally, model-based and tree-based methods support gene flow within and among the two octoploid species, including newly identified admixture in the Hawaiian F. chiloensis subsp. sandwicensis population that appears to be from an ancestral F. chiloensis population. Conclusion: F. virginiana and F. chiloensis are supported as monophyletic and sister lineages. All but one of the subspecies recognized within both octoploid species show extensive paraphyly. Furthermore, the phylogenetic relationship among F. chiloensis populations supports a single population range expansion southward from North America. The inter- and intraspecific relationships of octoploid strawberry are complex and suggest substantial and deep gene flow between sympatric populations among and within species.

Parental origins of the cultivated tetraploid sour cherry (Prunus cerasus L.)

“…The origin of tetraploid sour cherry ( P. cerasus ) has remained an open question due to limited sampling and low resolution of genomic data used in previous investigations. Advances in genomics have allowed for investigations of taxa with complex origins that were previously intractable (Bird et al, 2021; McKain et al, 2018; Vallejo‐Marín et al, 2016). We used whole plastomes and a rich set of nuclear genes to produce a robust phylogeny of cherry species, identify the progenitor species of the tetraploid sour cherry P. cerasus , and determine whether P. cerasus was formed from a single or multiple origins.…”

“…Their theory was supported by the intermediate morphological phenotypes of artificial hybridizations between sweet and ground cherry, overlapping native ranges, predominately disomic inheritance (Beaver & Iezzoni, 1993; Wang, 1998), and genomic in situ hybridization and karyotype analyses (Schuster & Schreibner, 1999). However, strong genomic and phylogenetic support for the origins of sour cherry, as well as insight into parentage and the number of allopolyploid origins, has been difficult to produce due to the technical challenges of generating and analyzing genomic data for polyploid genomes (Bird et al, 2021).…”