Biology subjects

Barrett, C. F.

Publications and source records attributed to Barrett, C. F..

10 recordsLinked to original sources

bioRxiv2026

Harnessing historical collections to reconstruct the invasion history of Microstegium vimineum (Poaceae)

The evolutionary processes underlying successful invasions are often difficult to disentangle. Historical collections provide a temporal perspective, offering great potential to reconstruct invasion histories and identify the processes driving invasions. Japanese stiltgrass (Microstegium vimineum) is an invasive C4 grass introduced to eastern North America over a century ago and now established in 31 USA states. To reconstruct its invasion history, we leveraged low-coverage whole-genome sequencing of 142 herbarium and 330 contemporary samples spanning the temporal and spatial extent of the North American invasion and the native range in Asia. We identified three independent introductions in the USA: an awnless form in the South and two independent introductions of awned forms in the North, with limited admixture among introductions across space and time. In both regions, we observed high genetic diversity in the earliest available collections despite demographic bottlenecks and identified several putative selective sweeps in or near flowering-time genes, suggesting rapid evolution in the introduced range. Our analyses support separate invasions in the USA, likely facilitated by standing genetic variation and selection, but provide little support for admixture playing a major role. Our study highlights the power of historical collections to uncover the processes and mechanisms underlying successful biological invasions.

evolutionary biology↗

bioRxiv2023

Plastid genome evolution in leafless members of the orchid subfamily Orchidoideae, with a focus on Degranvillea dermaptera

PremiseLeafless, heterotrophic plants are prime examples of organismal modification, the genomic consequences of which have received considerable interest. In particular, plastid genomes (plastomes) are being sequenced at a high rate, allowing continual refinement of conceptual models of reductive evolution in heterotrophs. Yet, numerous sampling gaps exist, hindering the ability to conduct comprehensive phylogenomic analyses in these plants. MethodsWe sequenced and analyzed the plastome of Degranvillea dermaptera, a rarely collected, leafless orchid species from South America about which little is known, including its phylogenetic affinities. Key ResultsWe revealed the most reduced plastome sequenced to date among the orchid subfamily Orchidoideae. Degranvillea has lost the majority of genes found in leafy autotrophic species, is structurally rearranged, and has similar gene content to the most reduced plastomes among the orchids. We found strong evidence for the placement of Degranvillea within the subtribe Spiranthinae using models that explicitly account for heterotachy, or lineage-specific evolutionary rate variation over time. We further found evidence of relaxed selection on several genes and correlations among substitution rates and several other "traits" of the plastome among leafless members of orchid subfamily Orchidoideae. ConclusionsOur findings advance knowledge on the phylogenetic relationships and paths of plastid genome evolution among the orchids, which have experienced more independent transitions to heterotrophy than any other plant family. This study demonstrates the importance of herbarium collections in comparative genomics of poorly known species of conservation concern.

evolutionary biology↗

bioRxiv2023

A case study of Whirly1 (WHY1) evolution in the angiosperms: altered sequence, splicing, and expression in a clade of early-transitional mycoheterotrophic orchids

The plastid-targeted transcription factor Whirly1 (WHY1) has been implicated in chloroplast biogenesis, plastid genome stability, and fungal defense response, which together represent characteristics of interest for the study of autotrophic losses across the angiosperms. While gene loss in the plastid and nuclear genomes has been well studied in mycoheterotrophic plants, the evolution of the molecular mechanisms impacting genome stability are completely unknown. Here we characterize the evolution of WHY1 in four early-transitional mycoheterotrophic orchid species in the genus Corallorhiza by synthesizing the results of phylogenetic, transcriptomic, and comparative genomic analyses with WHY1 genomic sequences sampled from 21 orders of angiosperms. We found an increased number of non-canonical WHY1 isoforms assembled from all but the greenest Corallorhiza species, including intron retention in some isoforms. Within Corallorhiza, phylotranscriptomic analyses revealed the presence of tissue-specific differential expression of WHY1 in only the most photosynthetically capable species and a coincident increase in the number of non-canonical WHY1 isoforms assembled from fully mycoheterotrophic species. Gene- and codon-level tests of WHY1 selective regimes did not infer significant signal of either relaxed selection or episodic diversifying selection in Corallorhiza, but did so for relaxed selection in the late-stage full mycoheterotrophic orchids Epipogium aphyllum and Gastrodia elata. Taken together, this study provides the most comprehensive view of WHY1 evolution in angiosperms to date. Our analyses reveal that splicing alteration and decreased expression of WHY1 are coincident with deceased plastome stability in a group of early-transitional mycoheterotrophic orchids and that these changes may precede the selective shifts observed in late-stage mycoheterotrophic species.

evolutionary biology↗

bioRxiv2023

A lack of population structure characterizes the invasive Lonicera japonica in West Virginia and across eastern North America

Invasive plant species cause massive ecosystem damage globally, yet represent powerful case studies in population genetics and rapid adaptation to new habitats. The availability of digitized herbarium collections data, and the ubiquity of invasive species across the landscape make them highly accessible for studies of invasion history and population dynamics associated with their introduction, establishment, spread, and ecological interactions. Here we focus on Lonicera japonica, one of the most damaging invasive vine species in North America. We leveraged digitized collections data and contemporary field collections to reconstruct the invasion history and characterize patterns of genomic variation in the eastern USA, using a straightforward method for generating nucleotide polymorphism data and a recently published, chromosome-level genome for the species. We found an overall lack of population structure among sites in northern West Virginia, USA, as well as across sites in the central and eastern USA. Heterozygosity and population differentiation were both low based on Fst, analysis of molecular variance, principal components analysis, and cluster-based analyses. We also found evidence of high inbreeding coefficients and significant linkage disequilibrium, in line with the ability of this otherwise outcrossing, perennial species to propagate vegetatively. Our findings corroborate earlier studies based on allozyme data, and suggest that intentional, human-assisted spread explains the lack of population structure, as this species was planted for erosion control and as an ornamental, escaping cultivation repeatedly across the USA. Finally, we discuss how plant invasion genomics can be incorporated into experiential undergraduate education as a way to integrate teaching and research.

plant biology↗

bioRxiv2023

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

Premise of the ResearchPlants remain underrepresented among species with sequenced mitochondrial genomes (mitogenomes), due to the difficulty in assembly with short-read technology. Invasive species lag behind crops and other economically important species in this respect, representing a lack of tools for management and land conservation efforts. MethodologyThe mitogenome of Microstegium vimineum, one of the most damaging invasive plant species in North America, was sequenced and analyzed using long-read data, providing a resource for biologists and managers. We conducted analyses of genome content, phylogenomic analyses among grasses and relatives based on mitochondrial coding regions, and an analysis of mitochondrial single nucleotide polymorphism in this invasive grass species. Pivotal ResultsThe assembly is 478,010 bp in length and characterized by two large, inverted repeats, and a large, direct repeat. However, the genome could not be circularized, arguing against a "master circle" structure. Long-read assemblies with data subsets revealed several alternative genomic conformations, predominantly associated with large repeats. Plastid-like sequences comprise 2.4% of the genome, with further evidence of Class I and Class II transposable element-like sequences. Phylogenetic analysis placed M. vimineum with other Microstegium species, excluding M. nudum, but with weak support. Analysis of polymorphic sites across 112 accessions of M. vimineum from the native and invasive ranges revealed a complex invasion history. ConclusionsWe present an in-depth analysis of mitogenome structure, content, phylogenetic relationships, and range-wide genomic variation in M. vimineums invasive US range. The mitogenome of M. vimineum is typical of other andropogonoid grasses, yet mitochondrial sequence variation across the invasive and native ranges is extensive. Our findings suggest multiple introductions to the US over the last century, with subsequent spread, secondary contact, long-distance dispersal, and possibly post-invasion selection on awn phenotypes. Efforts to produce genomic resources for invasive species, including sequenced mitochondrial genomes, will continue to provide tools for their effective management, and to help predict and prevent future invasions.

genomics↗

bioRxiv2021

The Ecology of Palm Genomes: Repeat-associated genome size expansion is constrained by aridity

O_LIGenome size varies 2,400-fold across plants, influencing their evolution through changes in cell size and cell division rates which impact plants environmental stress tolerance. Repetitive element expansion explains much genome size diversity, and the processes structuring repeat communities are analogous to those structuring ecological communities. However, which environmental stressors influence repeat community dynamics has not yet been examined from an ecological perspective. C_LIO_LIWe measured genome size and leveraged climatic data for 91% of genera within the ecologically diverse palm family (Arecaceae). We then generated genomic repeat profiles for 141 palm species, and analysed repeats using phylogenetically-informed linear models to explore relationships between repeat dynamics and environmental factors. C_LIO_LIWe show that palm genome size and repeat community composition are best explained by aridity. Specifically, EnSpm CACTA repeats were more abundant in palm species from wetter environments, which generally had larger genomes (>2.15Gbp/1C), suggesting amplification. In contrast, Ty1-copia Angela elements were more abundant in drier environments. C_LIO_LIOur results suggest water stress inhibits the expansion of repeats through selection on upper genome size limits. However, Ty1-copia Angela elements, which may associate with stress-response genes, have amplified in arid-adapted palm species. Overall, we provide novel evidence of climate influencing the assembly of repeat communities. C_LI

evolutionary biology↗

bioRxiv2021

Chromosome level genome assembly and annotation of highly invasive Japanese stiltgrass (Microstegium vimineum)

The invasive Japanese stiltgrass (Microstegium vimineum) affects a wide range of ecosystems and threatens biodiversity across the eastern USA. However, the mechanisms underlying rapid adaptation, plasticity, and epigenetics in the invasive range are largely unknown. We present a chromosome-level assembly for M. vimineum to investigate genome dynamics, evolution, adaptation, and the genomics of phenotypic plasticity. We generated a 1.12 Gb genome with scaffold N50 length of 53.44 Mb respectively, taking a de novo assembly approach that combined PacBio and Dovetail Genomics Omni-C sequencing. The assembly contains 23 pseudochromosomes, representing 99.96% of the genome. BUSCO assessment indicated that 80.3% of Poales gene groups are present in the assembly. The genome is predicted to contain 39,604 protein-coding genes, of which 26,288 are functionally annotated. Furthermore, 66.68% of the genome is repetitive, of which unclassified (35.63%) and long terminal repeat (LTR) retrotransposons (26.90%) are predominant. Similar to other grasses, Gypsy (41.07%) and Copia (32%) are the most abundant LTR-retrotransposon families. The majority of LTR-retrotransposons are derived from a significant expansion in the past 1-2 million years, suggesting the presence of relatively young LTR-retrotransposon lineages. We find corroborating evidence from Ks plots for a stiltgrass-specific duplication event, distinct from the more ancient grass-specific duplication event. The assembly and annotation of M. vimineum will serve as an essential genomic resource facilitating studies of the invasion process, the history and consequences of polyploidy in grasses, and provides a crucial tool for natural resource managers. SignificanceThe current lack of genomic resources for the invasive Japanese stiltgrass--and thousands of other invasive species globally--severely limits our understanding of the invasion process and hinders decision-making for effective management and control. In this study, we present a chromosome-level genome assembly and annotation of Japanese stiltgrass, a problematic weed in eastern North America, identifying a clear history of polyploidy and recent activity of transposable elements. The ultimate goal is to advance genomic studies to better understand the dynamics of non-native species during the various invasion phases, thereby providing insights into effective control strategies to manage current and future invasions.

genomics↗

bioRxiv2020

ISSRseq: an extensible, low-cost, and efficient method for reduced representation sequencing

O_LIThe capability to generate densely sampled single nucleotide polymorphism (SNP) data is essential in diverse subdisciplines of biology, including crop breeding, pathology, forensics, forestry, ecology, evolution, and conservation. However, the wet-lab expertise and bioinformatics training required to conduct genome-scale variant discovery remain limiting factors for investigators with limited resources. C_LIO_LIHere we present ISSRseq, a PCR-based method for reduced representation of genomic variation using simple sequence repeats as priming sites to sequence inter simple sequence repeat (ISSR) regions. Briefly, ISSR regions are amplified with single primers, pooled, used to construct sequencing libraries with a commercially-available kit, and sequenced on the Illumina platform. We also present a flexible bioinformatic pipeline that assembles ISSR loci, calls and hard filters variants, outputs data matrices in common formats, and conducts population analyses using R. C_LIO_LIUsing three angiosperm species as case studies, we demonstrate that ISSRseq is highly repeatable, necessitates only simple wet-lab skills and commonplace instrumentation, is flexible in terms of the number of single primers used, and can generate genomic-scale variant discovery on par with existing RRS methods which require more complex wet lab procedures. C_LIO_LIISSRseq represents a straightforward approach to SNP genotyping in any organism, and we predict that this method will be particularly useful for those studying population genomics and phylogeography of non-model organisms. Furthermore, the ease of ISSRseq relative to other RRS methods should prove useful to those lacking advanced expertise in wet lab methods or bioinformatics. C_LI

genomics↗

bioRxiv2020

Integrating genetics, morphology, and fungal host specificity in conservation studies of a vulnerable, selfing, mycoheterotrophic orchid

Mycoheterotrophic plants derive most or all carbon and nutrients from fungal partners and represent poorly understood components of forest biodiversity. Many are rare or endangered yet can be ecological indicators of forest ecosystem function due to their often highly specific fungal host requirements. One such species is the IUCN red-listed ( vulnerable), fully mycoheterotrophic orchid, Corallorhiza bentleyi. This recently described species is among the rarest plants in Appalachia, known from five counties in Virginia and West Virginia, USA. The species has a restricted range, small population size, and is self-pollinating. Here we take an integrative approach to conservation genetic assessment in C. bentleyi using floral morphometrics, simple-sequence repeats, and fungal host DNA to characterize variation within and among sampling localities. Morphology reveals some differentiation among individuals from six sampling localities. Surprisingly, most genetic variation is found within localities, contra to the expectation for a selfing species. Fungal host DNA reveals extreme specificity upon a few genotypes of a single ectomycorrhizal host species, Tomentella fuscocinerea, across all localities. We discuss the conservation implications of morphological, genetic, and symbiotic diversity in this vulnerable species, and recommend additional assessment of conservation status based on: an obligate reproductive mode of selfing, preventing benefits of outcrossing among genetically non-identical individuals; extreme host specificity, severely restricting niche space; and highly fragmented habitat under threat from anthropogenic disturbance. This study underscores the importance of integrative conservation assessment, analyzing multiple data sources, and reveals patterns not readily apparent from census-based assessments alone.

evolutionary biology↗

bioRxiv2020

Genetic, morphological, and niche variation in the widely hybridizing Rhus integrifolia-Rhus ovata species complex.

Hybridization and introgression are common processes among numerous plant species that present both challenges and opportunities for studies of species delimitation, phylogenetics, taxonomy, and adaptation. Rhus integrifolia and R. ovata are two ecologically important shrubs native to the southwestern USA and Mexico, and are known to hybridize frequently, but the morphological, genetic, and ecological implications of hybridization in these species are poorly studied on a broad geographic scale. Analyses were conducted using leaf morphology, genetic variation of plastid and nuclear loci, and species distribution models for both species and their putative hybrid introgressants across 19 localities in California and Arizona, USA. These analyses revealed evidence for morphological and genetic distinction among localities comprising putative parental species, but a high degree of morpho-genetic intermediacy among localities with putative hybrids. Comparison of morphological and genetic population structure among localities revealed evidence for putative local adaptation or widespread phenotypic plasticity. Multiple regression models identified a weak but statistically significant negative association between leaf area and precipitation. Finally, species distribution modeling inferred northward range shifts over time, with both species predicted to occupy more coastal regions in the future, possibly increasing the frequency of hybridization among them. These findings underscore the importance of integrative assessment of multiple data sources in the study of hybridizing species and highlight the Rhus integrifolia-ovata complex as a powerful model for investigating the adaptive implications of hybridization.

evolutionary biology↗