Digitized collections elucidate invasion history and patterns of awn polymorphism inMicrostegium vimineum

Abstract

Premise Digitized collections can help illuminate the mechanisms behind the establishment and spread of invasive plants. These databases provide a record of traits in space and time that allows for investigation of abiotic and biotic factors that influence invasive species. Methods Over 1100 digitized herbarium records were examined to investigate the invasion history and trait variation of Microstegium vimineum. Presence–absence of awns was investigated to quantify geographic patterns of this polymorphic trait, which serves several functions in grasses, including diaspore burial and dispersal to germination sites. Floret traits were further quantified, and genomic analyses of contemporary samples were conducted to investigate the history of M. vimineum's introduction and spread into North America. Results Herbarium records revealed similar patterns of awn polymorphism in native and invaded ranges of M. vimineum, with awned forms predominating at higher latitudes and awnless forms at lower latitudes. Herbarium records and genomic data suggested initial introduction and spread of the awnless form in the southeastern United States, followed by a putative secondary invasion and spread of the awned form from eastern Pennsylvania. Awned forms have longer florets, and floret size varies significantly with latitude. There is evidence of a transition zone with short‐awned specimens at mid‐latitudes. Genomic analyses revealed two distinct clusters corresponding to awnless and awned forms, with evidence of admixture. Conclusions Our results demonstrate the power of herbarium data to elucidate the invasion history of a problematic weed in North America and, together with genomic data, reveal a possible key trait in introduction success: presence or absence of an awn.

Mitochondrial genome sequencing and analysis of the invasiveMicrostegium vimineum: a resource for systematics, invasion history, and management

“…Our mitochondrial SNP analysis (Fig. 5B), and previous analysis of nuclear SNP variation (Barrett et al, 2022), support a scenario consistent with intensified, post-invasion selection for awn phenotypes in the eastern US, favoring awnless forms at lower latitudes and awned forms at higher latitudes. Habitat filtering may have also played a role (Weiher and Keddy, 1995), by selecting which phenotypes were successful in their initial invasions, with a higher likelihood of successful invasion hypothesized in the South by awnless forms, and by awned forms in the North.…”

“…5B). The finding of a predominantly “northern awned” clade and a “southern awnless” clade mirrors that based on nuclear SNP data (Barrett et al, 2022) and plastid data (Corbett C. W. et al, unpublished data). Further, there is evidence of multiple invasions and subsequent establishments from the native range, with a likely initial, successful “awnless” invasion in the southeastern US and at least one more successful invasion in the northeastern US of the awned form, likely in eastern Pennsylvania.…”

“…There is evidence that M. vimineum has experienced rapid adaptation after becoming established in the invasive range, in terms of flowering phenology across a latitudinal gradient, and growth/reproductive advantages of invasive populations compared with those in the native range, in line with the Evolution of Increased Competitive Ability hypothesis (Flory et al, 2011; Novy et al, 2013; Huebner et al, 2022). Barrett et al (2022) suggested that this may further extend to selection in the invasive range for different awn phenotypes. In the eastern US, there is a strong latitudinal pattern of awnless forms in the South, long-awned forms in the North, and intermediate- or short-awned forms at mid-latitudes.…”

“…Likely introduced as packing material for porcelain in the early 1900s (Fairbrothers and Gray, 1972), this species has spread to 30 US states, and is expanding into Canada, the northeastern US, and the northern US Midwest (Huebner, 2010a; 2010b; Mortensen et al, 2009; Rauschert et al, 2010; Barrett et al, 2022). Further, it is hypothesized that M. vimineum was introduced multiple times in the US, first in the southeastern US, and later in the Northeast, with subsequent spread and secondary contact, providing an apt case study in the genomic dynamics of the invasion process (Novy et al, 2013; Barrett et al, 2022). Recently published plastid and nuclear genomes are now available for this species (Welker et al, 2020; Ramachandran et al, 2021, respectively), but a complete mitogenome is lacking.…”

A lack of population structure characterizes the invasiveLonicera japonicain West Virginia and across eastern North America

“…Information from digitized collections databases provides a useful tool for reconstructing invasion routes and history, trait variation over space and time, and physical collections provide genomic resources for spatiotemporal analysis of variation (e.g. Gallinat et al 2018; Barrett et al 2022; Bieker et al 2022; Heberling 2022). In parallel, advances in genomic sequencing (RAD-seq, GBS, low-coverage whole genome sequencing, sequence capture, multiplexed amplicon sequencing) provide increased power over previous methods (allozyme variation, organellar gene/spacer sequencing, microsatellites) for studies of genetic variation and population structure, with broader representation of the genome for detecting both neutral and adaptive variation (Chown et al 2015; Hamelin and Roe 2020; North et al 2021).…”