Deep sequencing of amplicons reveals widespread intraspecific hybridization and multiple origins of polyploidy in big sagebrush (Artemisia tridentata; Asteraceae)

Abstract

• Premise of the study: Hybridization has played an important role in the evolution and ecological adaptation of diploid and polyploid plants. Artemisia tridentata (Asteraceae) tetraploids are extremely widespread and of great ecological importance. These tetraploids are often taxonomically identified as A. tridentata subsp. wyomingensis or as autotetraploids of diploid subspecies tridentata and vaseyana. Few details are available as to how these tetraploids are formed or how they are related to diploid subspecies.• Methods: We used amplicon sequencing to assess phylogenetic relationships among three recognized subspecies: tridentata, vaseyana, and wyomingensis. DNA sequence data from putative genes were pyrosequenced and assembled from 329 samples. Nucleotide diversity and putative haplotypes were estimated from the high‐read coverage. Phylogenies were constructed from Bayesian coalescence and neighbor‐net network analyses.• Key results: Analyses support distinct diploid subspecies of tridentata and vaseyana in spite of known hybridization in ecotones. Nucleotide diversity estimates of populations compared to the total diversity indicate the relationships are predominately driven by a small proportion of the amplicons. Tetraploids, including subspecies wyomingensis, are polyphyletic occurring within and between diploid subspecies groups.• Conclusions: Artemisia tridentata is a species comprising phylogenetically distinct diploid progenitors and a tetraploid complex with varying degrees of phylogenetic and morphological affinities to the diploid subspecies. These analyses suggest tetraploids are formed locally or regionally from diploid tridentata and vaseyana populations via autotetraploidy, followed by introgression between tetraploid groups. Understanding the phylogenetic vs. ecological relationships of A. tridentata subspecies will have bearing on how to restore these desert ecosystems.

Signals of speciation: volatile organic compounds resolve closely related sagebrush taxa, suggesting their importance in evolution

“…VOCs appear to be at least as reliable as the current methodology: morphology and within‐plant chemistry. VOCs also appear to be more reliable than recent studies employing molecular markers (Richardson et al ., ). The Random Forest algorithm correctly identified 67 of the 70 (96%) plants sampled using VOCs.…”

“…As described in Richardson et al . (), tissue samples were used to evaluate ploidy and UV fluorescence (Stevens & McArthur, ) for all samples from the Shrub Sciences Laboratory and Orchard garden. Select plants ( n = 12) at Majors Flat were also tested for UV fluorescence and ploidy using flow cytometry.…”

Considering ploidy when producing and using mixed‐source native plant materials for restoration

“…In addition, if IPV is identified, there are practical limitations to incorporating it into production and sourcing decisions. Indeed, we know of only four species in the United States where IPV has been assessed, mapped, and explicitly incorporated into guidelines for sourcing: sagebrush ( Artemisia tridentata ) (Mahalovich & McArthur ; Richardson et al ), fourwing saltbush ( Atriplex canescens ) (Sanderson & McArthur ), Leymus cinereus (Johnson & Vance‐Borland ), and Pseudoroegneria spicata (Gibson et al ). Even for these species, the challenges of whether or when to mix cytotypes in a nursery or restoration setting have only been addressed explicitly for one species (Gibson et al ).…”

The potential of novel native plant materials for the restoration of novel ecosystems

“…Recently, it been discovered that ssp. wyomingensis originates via the hybridization of these two parental subspecies (Richardson et al, 2012). Furthermore, ssp.…”

“…Furthermore, ssp. wyomingensis is polyphyletic, meaning such hybridization events have occurred independently at multiple times and places (Richardson et al, 2012).…”