Unweaving the population structure and genetic diversity of Canadian shrub willow

Abstract

Perennial shrub willow are increasingly being promoted in short-rotation coppice systems as biomass feedstocks, for phytoremediation applications, and for the diverse ecosystem services that can accrue. This renewed interest has led to widespread willow cultivation, particularly of non-native varieties. However, Canadian willow species have not been widely adopted and their inherent diversity has not yet been thoroughly investigated. In this study, 324 genotypes of Salix famelica and Salix eriocephala collected from 33 sites of origin were analyzed using 26,016 single nucleotide polymorphisms to reveal patterns of population structure and genetic diversity. Analyses by Bayesian methods and principal component analysis detected five main clusters that appeared to be largely shaped by geoclimatic variables including mean annual precipitation and the number of frost-free days. The overall observed (HO) and expected (HE) heterozygosity were 0.126 and 0.179, respectively. An analysis of molecular variance revealed that the highest genetic variation occurred within genotypes (69%), while 8% of the variation existed among clusters and 23% between genotypes within clusters. These findings provide new insights into the extent of genetic variation that exists within native shrub willow species which could be leveraged in pan-Canadian willow breeding programs.

Phylogenomics reveals patterns of ancient hybridization and differential diversification contributing to phylogenetic conflict inPopulusL. andSalixL

“…As others have argued for Populus (Cronk et al 2018), this pattern of ongoing speciation with hybridization may be best represented as a syngameon (Lotsy 1925) and may exhibit emergent properties such as the ability to draw on elevated levels of standing variation for adaptive evolution (Cannon et al 2020; Cannon 2021). Envisioning Salix as a syngameon redefines evolutionary units as larger combinations of hybridizing species and our data and previous results (Hardig et al 2000; Murphy et al 2022) suggest that the Salix syngameon exhibits a complex web of ongoing hybridization and partial reproductive isolation that has persisted for millions of years.…”

Challenge accepted: Evolutionary lineages versus taxonomic classification of North American shrub willows (Salix)

“…Due to the high amount of hybridization in willows and the conflicting signals observed in their target enrichment data set, Sanderson et al (2023) described Salix as a syngameon, that is, a species complex of related taxa with frequent hybridization and partial reproductive isolation. This pattern has also been shown in other willow studies (Hardig et al, 2000; Murphy et al, 2022) and has been well studied in oaks (Hipp et al, 2020). In this study, we did not focus on hybrid evolution in willows, but were aiming to provide a robust backbone phylogeny.…”