Marlene Hahn

Marlene Hahn
Morton Arboretum · Research

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29
Publications
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Publications

Publications (29)
Article
Ecological opportunity has been associated with increases in diversification rates across the tree of life. Under an ecological diversification model, the emergence of novel environments promotes morpho‐ and ecospace evolution. Whether this model holds at the clade‐level within the most species‐rich angiosperm genus found in North America (Carex, C...
Article
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Carex section Schiedeanae (subg. Euthyceras) has long been thought to comprise at most five species of Mexican sedges. Our morphological studies in the field and herbarium, however, supported by more recent DNA sequencing work, demonstrate that the section is in fact three times as species‐rich, making it one of the largest sections in Mexico. Its...
Article
A RAD-seq phylogeny is presented for the genus Ulmus , and a revised infrageneric classification is given, with keys, descriptions, and range maps for the subgenera and sections. The previously accepted classification was based on a cpDNA phylogeny, but several well-marked clades in the chloroplast phylogeny are not recovered in the RAD-seq phyloge...
Article
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Phylogenetic studies of Carex L. (Cyperaceae) have consistently demonstrated that most subgenera and sections are para‐ or polyphyletic. Yet taxonomists continue to use subgenera and sections in Carex classification. Why? The Global Carex Group here takes the position that the historical and continued use of subgenera and sections serves to (1) org...
Article
The field of systematics is experiencing a new molecular revolution driven by the increased availability of high-throughput sequencing technologies. As these techniques become more affordable, the increased genomic resources have increasingly far-reaching implications for our understanding of the Tree of Life. With c. 2000 species, Carex (Cyperacea...
Cover Page
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Carex (Cyperaceae) is a megadiverse genus which ranks among the five largest angiosperm genera, with about 2000 species. The authors investigated the main biogeographic and lineage diversification history in the genus using a global phylogenetic sampling comprising 66% of accepted species. The study suggests that there may not be just one answer to...
Article
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In phylogenetic studies across angiosperms, at various taxonomic levels, polytomies have persisted despite efforts to resolve them by increasing sampling of taxa and loci. The large amount of genomic data now available and statistical tools to analyze them provide unprecedented power for phylogenetic inference. Targeted sequencing has emerged as a...
Article
Full-text available
The megadiverse genus Carex (c. 2000 species, Cyperaceae) has a nearly cosmopolitan distribution, displaying an inverted latitudinal richness gradient with higher species diversity in cold‐temperate areas of the Northern Hemisphere. Despite great expansion in our knowledge of the phylogenetic history of the genus and many molecular studies focusing...
Article
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The tree of life is highly reticulate, with the history of population divergence emerging from populations of gene phylogenies that reflect histories of introgression, lineage sorting and divergence. In this study, we investigate global patterns of oak diversity and test the hypothesis that there are regions of the oak genome that are broadly infor...
Article
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The eastern North American white oaks, a complex of approximately 16 potentially interbreeding species, have become a classic model for studying the genetic nature of species in a syngameon. Genetic work over the past two decades has demonstrated the reality of oak species, but gene flow between sympatric oaks raises the question of whether there a...
Article
Climatic niche modeling is widely used in modern macroecology and evolutionary biology to model species' distributions and ecological niches. Frequently, Global Biodiversity Information Facility (GBIF) distribution data are used as raw data for such models. Unfortunately, the accuracy of resulting niche estimates is difficult to assess, and GBIF us...
Preprint
Full-text available
The eastern North American white oaks, a complex of approximately 16 potentially interbreeding species, have become a classic model for studying the genetic nature of species in a syngameon. Genetic work over the past two decades has demonstrated the reality of oak species, but gene flow between sympatric oaks raises the question of whether there a...
Preprint
The tree of life is highly reticulate, with the history of population divergence buried amongst phylogenies deriving from introgression and lineage sorting. In this study, we test the hypothesis that there are regions of the oak ( Quercus , Fagaceae) genome that are broadly informative about phylogeny and investigate global patterns of oak diversit...
Article
Meiotic drive, the class of meiotic mechanisms that drive unequal segregation of alleles among gametes, may be an important force in karyotype evolution. Its role in holocentric organisms, whose chromosomes lack localized centromeres is poorly understood. We crossed two individuals of Carex scoparia (Cyperaceae) with different chromosome numbers (2...
Article
The evolutionary history of Quercus section Cyclobalanopsis, a dominant lineage in East Asian evergreen broadleaved forests (EBLFs), has not been comprehensively studied using molecular tools. In this study, we reconstruct the first comprehensive phylogeny of this lineage using a genomic approach (restriction-site associated DNA sequencing, RAD-seq...
Article
Full-text available
DNA barcoding has proved difficult in a number of woody plant genera, including the ecologically important oak genus Quercus. In this study, we utilized restrictionsite‐associated DNA sequencing (RAD‐seq) to develop an economical single nucleotide polymorphism (SNP) DNA barcoding system that suffices to distinguish eight common, sympatric eastern N...
Article
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Oaks (Quercus, Fagaceae) are the dominant tree genus of North America in species number and biomass, and Mexico is a global center of oak diversity. Understanding the origins of oak diversity is key to understanding biodiversity of northern temperate forests. A phylogenetic study of biogeography, niche evolution and diversification patterns in Quer...
Article
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Seven papers in this quarter's issue of Systematic Botany come from a symposium on phylogeny and ecological diversification in sedges (Carex L., Cyperaceae) convened at the Botany 2015 meetings in Edmonton. The symposium was timely, as the genus had recently been circumscribed to include the four segregate genera Cymophyllus Mack., Kobresia Willd.,...
Article
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Major public DNA databases — NCBI GenBank, the DNA DataBank of Japan (DDBJ), and the European Molecular Biology Laboratory (EMBL) — are invaluable biodiversity libraries. Systematists and other biodiversity scientists commonly mine these databases for sequence data to use in phylogenetic studies, but such studies generally use only the taxonomic id...
Article
Full-text available
We present the first large-scale phylogenetic hypothesis for the genus Carex based on 996 of the 1983 accepted species (50.23%). We used a supermatrix approach using three DNA regions: ETS, ITS and matK. Every concatenated sequence was derived from a single specimen. The topology of our phylogenetic reconstruction largely agreed with previous studi...
Article
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Premise of the study: Understanding the drivers of speciation is a central task of evolutionary biology. Chromosomal rearrangements are known to play an important role in species diversification, but the role of rearrangements of holocentric chromosomes-chromosomes without localized centromeres-is poorly understood. Methods: We made numerous art...
Article
We undertook a three-year collaboration with two area schools to generate novel data on the morphological diversity of sedges (Carex: Cyperaceae). Our goals were to generate novel, specimen-based morphometric data that we and the students could use to investigate plant diversification and to mentor students in all aspects of science: hypothesis gen...
Article
Full-text available
Carex (Cyperaceae), with an estimated 2000 species, nearly cosmopolitan distribution and broad range of habitats, is one of the largest angiosperm genera and the largest in the temperate zone. In this article, we provide argument and evidence for a broader circumscription of Carex to add all species currently classified in Cymophyllus (monotypic),...
Article
Section Radicales (Kük.) Nelmes comprises nearly 15 species in Carex subg. Carex (Cyperaceae) and is mainly distributed in the Pan-Himalaya region, with a few species extending to the Guangxi and Hainan provinces of China and Burma. A taxonomic revision of sect. Radicales in China is proposed and 12 species with two varieties are recognized. Carex...
Article
Full-text available
Community assembly entails a filtering process, where species found in a local community are those that can pass through environmental (abiotic) and biotic filters and successfully compete. Previous research has demonstrated the ability of white-tailed deer (Odocoileus virginianus) to reduce species diversity and favour browse-tolerant plant commun...
Article
Bacterial spores are surrounded by a morphologically complex, mechanically flexible protein coat, which protects the spore from toxic molecules. The interactions among the over 50 proteins that make up the coat remain poorly understood. We have used cell biological and protein biochemical approaches to identify novel coat proteins in Bacillus subti...
Article
Full-text available
Bacillus spores are protected by a structurally and biochemically complex protein shell composed of over 50 polypeptide species, called the coat. Coat assembly in Bacillus subtilis serves as a relatively tractable model for the study of the formation of more complex macromolecular structures and organelles. It is also a critical model for the disco...

Projects

Projects (2)
Project
Chromosome evolution is one of the most important drivers of biodiversity. Much research into chromosome evolution has focused on physiological and ecological implications of polyploidy. Because polyploidy entails changes in DNA content and gene number, expression differences associated with polyploidization can have dramatic effects on phenotype. Another important body of research has focused on the effects of chromosome inversions on promoting species differentiation through the protection of ecologically significant gene combinations from recombination. Almost completely ignored have been the biodiversity implications of other types of chromosome rearrangements that result in chromosome number changes with little or no change in DNA content (viz., fission and fusion). HoloChromEvol project propose a unique integration of genomic, cytogenetic, and ecological experiments to investigate the effects of chromosome evolution on the biodiversity of the largest flowering plant genus of the temperate zone, the sedges of genus Carex (Cyperaceae). The genus is emerging as a model system for studying chromosomal speciation in holocentric species, species in which the centromere is not a localized structure, but distributed along the entire length of the chromosome. Our research will provide novel insights into the relationship between chromosome evolution, recombination rate, local adaptation, and life history strategies: ultimately, the ecological underpinnings of biodiversity. It will also provide the genomic and genetic resources needed to establish Carex as a model system for understanding chromosome evolution across the tree of life, in all lineages in which chromosome evolution proceeds primarily by fission, fusion, and translocations. The overarching goal of our long-term research program is to elucidate how chromosome evolution affects biodiversity patterns across the tree of life. HoloChromEvol is an important key to this goal, and will place us in a position to make substantial, career-long contributions in the field of biodiversity science. Through an integration of cutting-edge genomic and ecological experiments in a hyper-diverse flowering plant genus with exceptional chromosomal variation, this project will tease apart the mechanisms by which holocentric chromosome evolution drives genetic diversification and identify the population dynamic elements that allow for chromosomal diversification in sedges. The result will be a model of diversification in this keystone genus that integrates the dynamics of population establishment, migration, and persistence with the chromosomal and genomic architecture of population divergence.