Oceanic islands and archipelagos are natural laboratories for investigating patterns and processes of evolution. Islands change with the course of time, resulting in a dynamic ontogeny over millions ...of years. The combined forces of tectonic plate subsidence and erosion from waves, wind, and rainwater bring about substantial geomorphological change over millions of years, until islands eventually disappear under the sea. Added to these long‐term natural changes to the environment of the islands are the changes caused by human activities in recent centuries. After humans reach a previously unpopulated island, they utilize the natural resources for their own survival, cutting forests for making houses, boats, and firewood. The size of the human population and the length of time on the island determine the degree of environmental impact. Evolutionary processes in plants of oceanic islands take place during ontogeny of the islands, resulting in population divergence, speciation, and hybridization. Due to the dramatic alterations suffered by many islands over millions of years, the present patterns of distribution and ecology of species within endemic groups may have little to do with the patterns when the species originated. Understanding these environmental changes is fundamental to infer a founder effect, reasons for levels of genetic variation within and among populations, and modes of speciation. Special caution must be exercised while making comparisons between groups located on islands of different geological ages and that have endured differing environmental modifications from humans. Examples are provided from the Juan Fernández Archipelago and Lord Howe Island.
Abstract
Asteraceae subfamily Barnadesioideae (ten genera, c. 90 species), confined to South America, are sister to the remainder of the family. The relative antiquity of the barnadesioids might lead ...one to expect that they contain more wood features plesiomorphic for the family, but only one character clearly falls in that category. Pits on imperforate tracheary elements are bordered (except for annuals), whereas simple pits occur in two related families, Calyceraceae (part) and Stylidiaceae (all that have been examined); in Goodeniaceae bordered pits only occur. By attaining fully bordered pits in Chuquiraga, the imperforate tracheary elements qualify as an apomorphy, ‘neotracheids’, valuable for resisting embolism formation in dry and cold South American habitats. Neotracheids are found also in Loricaria (Asteraceae: Inuleae), also from these habitats. Neotracheids, like plesiomorphic tracheids, are conductive, unlike fibre tracheids and libriform fibres. Other barnadesioid wood characters adapted to cold and drought include grouping of vessels, high vessel density, shorter vessel elements and helical sculpture (including helical thickenings on lumen-facing walls) of secondary xylem vessels. In Chuquiraga and Dasyphyllum, these helical thickenings are bordered in some species (new report for angiosperms). Some of the barnadesioid adaptations to cold and drought can be found in North American Artemisia spp. (Asteraceae: Anthemideae), especially in montane and desert areas. Wood features of barnadesioids match their respective habits and habitats: a few trees; shrubs of humid, dry or desert areas; a distinctive rhizomatous succulent in the pampas (Schlechtendalia); a scree/gravel perennial (Huarpea) and two genera of annuals, one with succulent leaves (Duseniella) and one with rayless (at least at first) stems in arid and open soils (Doniophyton). Diversity is unusual considering the small size of the subfamily. Examples of endodermal crystals (Arnaldoa only), pith sclereids and primary xylem fibres are cited.
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•Molecular phylogeny of subtribe Ambrosiinae (Asteraceae).•Ambrosiinae found to be fairly monophyletic.•Close relationship of Dugesia (part of subtribe Engelmanniinae) with ...Ambrosiinae.•Subdivision of Ambrosiinae into “Iveae” and “Ambrosieae” not corroborated.
Ambrosiinae are one of the most distinct subtribes in the Heliantheae alliance (Asteraceae), mainly due to specialization toward wind pollination. Taxa of the subtribe are principally native to the Americas, although some species have attained a cosmopolitan distribution.
Members of subtribe Engelmanniinae are considered close to Ambrosiinae, due to shared morphological traits. However, the placement of Ambrosiinae within the Heliantheae alliance has not yet been corroborated by phylogenetic analyses. In the present study, we test the circumscription of subtribe Ambrosiinae and examine relationships among its genera. We used sequence information from three plastid (psbA-trnH, trnQ-rps16 and trnL-F) and two nuclear (ITS and D35) marker regions. Phylogenetic inference analyses were conducted, applying Bayesian Inference (BI) and Maximum Likelihood (ML).
Subtribe Ambrosiinae is found monophyletic or nearly so in all analyses. The genera Dugesia and Rojasianthe (previously considered part of subtribe Engelmanniinae) in some cases cluster together with Ambrosiinae; these genera are clearly not part of Engelmanniinae. Within Ambrosiinae, the genera Parthenium and Parthenice occupy basal positions, whereas members of the genus Ambrosia are the most derived representatives of the subtribe. Previous subdivision of Ambrosiinae into “Iveae” (members having androgynous capitula and free achenes) and “Ambrosieae” (genera with unisexual heads and achenes enclosed in burs) is not corroborated. Results also allow consideration of relationships among species and subgeneric groups within Parthenium, Iva, and Ambrosia.
Dating the Species Network Mccann, Jamie; Jang, Tae-Soo; Macas, JiřI ...
Systematic biology,
11/2018, Letnik:
67, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Allopolyploidy has played an important role in the evolution of the flowering plants. Genome mergers are often accompanied by significant and rapid alterations of genome size and structure via ...chromosomal rearrangements and altered dynamics of tandem and dispersed repetitive DNA families. Recent developments in sequencing technologies and bioinformatic methods allow for a comprehensive investigation of the repetitive component of plant genomes. Interpretation of evolutionary dynamics following allopolyploidization requires both the knowledge of parentage and the age of origin of an allopolyploid. Whereas parentage is typically inferred from cytogenetic and phylogenetic data, age inference is hampered by the reticulate nature of the phylogenetic relationships. Treating subgenomes of allopolyploids as if they belonged to different species (i.e., no recombination among subgenomes) and applying cross-bracing (i.e., putting a constraint on the age difference of nodes pertaining to the same event), we can infer the age of allopolyploids within the framework of the multispecies coalescent within BEAST2. Together with a comprehensive characterization of the repetitive DNA fraction using the RepeatExplorer pipeline, we apply the dating approach in a group of closely related allopolyploids and their progenitor species in the plant genus Melampodium (Asteraceae). We dated the origin of both the allotetraploid, Melampodium strigosum, and its two allohexaploid derivatives, Melampodium pringlei and Melampodium sericeum, which share both parentage and the direction of the cross, to the Pleistocene (<1.4 Ma). Thus, Pleistocene climatic fluctuations may have triggered formation of allopolyploids possibly in short intervals, contributing to difficulties in inferring the precise temporal order of allopolyploid species divergence of M. sericeum and M. pringlei. The relatively recent origin of the allopolyploids likely played a role in the near-absence of major changes in the repetitive fraction of the polyploids’ genomes. The repetitive elements most affected by the postpolyploidization changes represented retrotransposons of the Ty1-copia lineage Maximus and, to a lesser extent, also Athila elements of Ty3-gypsy family.
Abstract
Based on molecular phylogenetic studies, Barnadesioideae have been proposed to be the basal subfamily of Asteraceae. This is a complex of 10 genera and 87 species distributed primarily along ...the Andean mountains, Patagonia, and into southern Brazil and Uruguay. Phylogenetic analyses have recovered all genera as monophyletic groups and have provided insights to their inter-relationships. Four generic clades have been substantiated: (1) Chuquiraga, Doniophyton, and Duseniella; (2) Dasyphyllum; (3) Barnadesia and Huarpea; and (4) Archidasyphyllum, Arnaldoa, and Fulcaldea. The remaining genus, the monospecific Schlechtendalia, has been an outlier in the subfamily, with some previous analyses recovering it as basal for the entire subfamily, and others showing it as sister to Barnadesia and Huarpea (with weak support) as well as to other genera. Recent massive sampling of loci has confirmed Schlechtendalia as the sister genus for the subfamily. Schlechtendalia luzulifolia has morphology atypical for Asteraceae. The capitula are loose aggregations of florets, and the leaves are long and strap shaped, more reminiscent of monocots. Morphological and anatomical investigations of the leaves reveal long, laminar blades with parallelodromous vascularization. The vesture is often with ‘barnadesioid trichomes’, especially towards the base of the plant, plus additional uniseriate trichomes consisting of 3 to many cells, newly reported for the subfamily. Some glandular trichomes with 2-4 short cells also occur. The transverse anatomy of the leaves reveals a single epidermal layer on both surfaces, which also contain the stomata (the leaf being amphistomatic). The mesophyll is undifferentiated; the vascular traces are surrounded by sclerenchyma that not only encircles the traces but also extends towards the epidermis and connects with it. The morphology and anatomy of the leaves of Schlechtendalia are divergent in comparison with other genera of the subfamily. Chuquiraga, Doniophyton, and Huarpea have leaf adaptations for survival in xeric habitats, such as dense pubescence, grey surfaces, and revolute margins. Schlechtendalia, in contrast, is adapted to a more mesic environment, especially near the Atlantic Ocean and along the Uruguay and La Plata rivers. The leaves are oriented upright, which correlates with undifferentiated mesophyll and stomata on both epidermal layers. The stem is an underground rhizome, an adaptation that permits survival during seasonal drought in the austral summer in Uruguay and adjacent regions. It is hypothesized that Schlechtendalia may have become adapted to more mesic environments in the Miocene prior to the rise of the Andes and development of the modern arid environments, into which many of the other genera of the subfamily subsequently radiated.
Plant genomes vary greatly in composition and size mainly due to the diversity of repetitive DNAs and the inherent propensity for their amplification and removal from the host genome. Most studies ...addressing repeatome dynamics focus on model organisms, whereas few provide comprehensive investigations across the genomes of related taxa. Herein, we analyze the evolution of repeats of the 13 species in
sect.
, representing all but two of its diploid taxa, in a phylogenetic context. The investigated genomes range in size from 0.49 to 2.27 pg/1C (ca. 4.5-fold variation), despite having the same base chromosome number (
= 10) and very strong phylogenetic affinities. Phylogenetic analysis performed in BEAST and ancestral genome size reconstruction revealed mixed patterns of genome size increases and decreases across the group. High-throughput genome skimming and the RepeatExplorer pipeline were utilized to determine the repeat families responsible for the differences in observed genome sizes. Patterns of repeat evolution were found to be highly correlated with phylogenetic position, namely taxonomic series circumscription. Major differences found were in the abundances of the SIRE (
), Athila (
), and
(DNA transposon) lineages. Additionally, several satellite DNA families were found to be highly group-specific, although their overall contribution to genome size variation was relatively small. Evolutionary changes in repetitive DNA composition and genome size were complex, with independent patterns of genome up- and downsizing throughout the evolution of the analyzed diploids. A model-based analysis of genome size and repetitive DNA composition revealed evidence for strong phylogenetic signal and differential evolutionary rates of major lineages of repeats in the diploid genomes.
Las floras de los países de América Latina ofrecen oportunidades para investigar temas numerosos y significativos, como son la adaptación en ambientes diversos, la biogeografía de islas, la ...especiación en ecosistemas de la alta montaña, la evolución en zonas tropicales, y los impactos de la glaciación durante el Pleistoceno. Estas perspectivas amplias traspasan las fronteras de los países, lo cual sugiere el desarrollo de colaboraciones internacionales. Latinoamérica contiene ca. 110,000 especies vasculares y nativas, lo que representa aproximadamente un 29% de la flora mundial. Falta todavía un inventario más preciso para la construcción de clasificaciones más predictivas y la interpretación de procesos de macro- y microevolución. Una solución para llegar a un inventario más completo puede ser la contratación de un nivel numeroso de jóvenes en necesidad de ayuda económica como parataxónomos, todos ellos organizados en un Cuerpo de Patrimonio Nacional dentro de cada país. Otra prioridad es la monografía botánica, especialmente con enfoques evolutivos amplios. El acceso a la literatura y fotos digitales de muestras del herbario apoyan el trabajo monográfico como nunca antes. Los viajes al campo que cruzan fronteras internacionales son indispensables para investigar las relacciones evolutivas dentro de grupos naturales. El Internet ofrece oportunidades para publicar monografías con más contenido visual, lo cual puede servir mejor a otros sectores de la sociedad. Los factores de impacto se han aceptado mundialmente para la evaluación administrativa del éxito profesional, y se recomienda que se adopten estrategias para maximizar su utilidad en el desarrollo de una carrera profesional. Para estimular las investigaciones colaborativas entre científicos de países fuera de América Latina, se sugiere aumentar la competencia del inglés, incluyendo el uso de este idioma durante las presentaciones que se efectúan en conferencias internacionales. Además, un dominio del inglés abre las puertas a la literatura mundial y apoya las investigaciones sobre temas biológicos internacionales en vez de sólo regionales.
Despite the broad acceptance of phylogenetic principles in biological classification, a fundamental question still exists on how to classify paraphyletic groups. Much of the controversy appears due ...to (1) historical shifts in terminology and definitions, (2) neglect of focusing on evolutionary processes for understanding origins of natural taxa, (3) a narrow perspective on dimensions involved with reconstructing phylogeny, and (4) acceptance of lower levels of information content and practicability as a trade-off for ease of arriving at formal classifications. Monophyly in evolutionary biology originally had a broader definition, that of describing a group with common ancestry. This definition thus includes both paraphyletic and monophyletic groups in the sense of Hennig. We advocate returning to a broader definition, supporting use of Ashlock's term holophyly as replacement for monophyly s.str. By reviewing processes involved in the production of phylogenetic patterns (budding, merging, and splitting), we demonstrate that paraphyly is a natural transitional stage in the evolution of taxa, and that it occurs regularly along with holophyly. When a new holophyletic group arises, it usually coexists for some time with its paraphyletic stem group. Paraphyly and holophyly, therefore, represent relational and temporal evolutionary stages. Paraphyletic groups exist at all levels of diversification in all kingdoms of eukaryotes, and they have traditionally been recognized because of their descent-based similarity. We review different methodological approaches for recognition of monophyletic groups s.l. (i.e., both holophyletic and paraphyletic), which are essential for discriminating from polyphyly that is unacceptable in classification. For arriving at taxonomic decisions, natural processes, information content, and practicability are essential criteria. We stress using shared descent as a primary grouping principle, but also emphasize the importance of degrees of divergence plus similarity (cohesiveness of evolutionary features) as additional criteria for classification.
Loss of genetic diversity reduces the ability of species to evolve and respond to environmental change. Araucaria araucana is an emblematic conifer species from southern South America, with important ...ethnic value for the Mapuche people (Pehuenche); the Chilean Government has catalogued its conservation status as vulnerable. Climatic fluctuations were potentially a major impact in the genetic variation within many tree species. In this context, the restricted geographic distribution of A. araucana in Chile appears to be a consequence of the Last Glacial Maximum (LGM). During the past two centuries, strong human intervention has also affected the geographical distribution and population sizes of A. araucana. Reduction of population size may cause loss of genetic diversity, which could affect frequency of adaptive loci. The aims of this study were to know the existence of potential loci under selection and populations with genetic, demographic disequilibrium in the Chilean distribution of A. araucana. Based on 268 polymorphic AFLP loci, we have investigated potential loci under selection and genetic, demographic disequilibrium within seven Chilean populations of Araucaria araucana. Correlation of 41 outlier loci with the environmental variables of precipitation and temperature reveals signatures of selection, whereas 227 neutral loci provide estimates of demographic equilibrium and genetic population structure. Three populations are recommended as priorities for conservation.
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