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Splitting of Micrasterias fimbriata (Desmidiales, Viridiplantae) into two monophyletic species and description of Micrasterias compereana sp. nov
Abstract
Background – Micrasterias fimbriata, a conspicuous desmid species, has recently been shown to be composed of two clearly delimited monophyletic clades within the genus Micrasterias, closely related to several other well-defined Micrasterias species
(M. brachyptera, M. rotata, M. torreyi). The members of both clades can also be unambiguously recognized by careful morphological analysis. In addition, their distribution areas in Europe and North America are largely vicariant. Interestingly, morphological features of one of
the clades do not correspond with any of the previously described infraspecific taxa of M. fimbriata.
Material and methods – The study was based on a combination of morphological and molecular phylogenetic analyses of the clonal strains and natural populations.
Key results and conclusions – In this study, we present formal taxonomic description of Micrasterias compereana for specimens formerly included within traditional M. fimbriata, but differring in their phylogenetic position and discriminative morphological characteristics.
Phylogenetic analysis was based on the nuclear 18S rDNA and the plastid-encoded trnGUCC
intron sequence data. Morphological differences between species were illustrated by light and scanning electron microscopy. The analysis of natural samples, strains and published records
showed that M. compereana occurs in North America and western Europe. Conversely, M. fimbriata sensu stricto probably only occurs in temperate and boreal regions of Europe and Asia.
... Recent molecular studies led to major changes in the taxonomy of desmids (McCourt et al. 2000;Gontcharov 2008;Gontcharov & Melkonian 2004Hall et al. 2008;Neustupa et al. 2010Neustupa et al. , 2011Neustupa et al. , 2014Nemjová et al. 2011;Škaloud et al. 2011Šťastný et al. 2013). Such advances raised questions about the taxonomic value of many morphological characters traditionally used for classification in the group, challenging species concepts in the family and questioning the large number of infraspecific taxa identified only by morphological criteria (Gontcharov & Melkonian 2008;Neustupa et al. 2010). ...
... Micrasterias is one of the most studied and well-known genera of Desmidiaceae, especially from the molecular phylogenetic point of view. Recent studies using the combination of molecular and morphological methods revealed the difference within closely related species and/or species complexes within the genus (Neustupa et al. 2010(Neustupa et al. , 2014Nemjová et al. 2011;Škaloud et al. 2011;Neustupa & Šťastný 2018). Previous phylogenetic studies revealed that the Micrasterias lineage comprises at least eight monophyletic lineages that were named A-H (Škaloud et al. 2011), and that the genus includes taxa with morphology ranging from relatively simple elliptic semicells without any marked incision, as is the case of Micrasterias ralfsii (Brébisson ex Ralfs) Škaloud, Nemjová, Veselá, Černá & Neustupa, to the very complex starlike shape (Neustupa 2016). ...
... Studies based on polyphasic approaches are important for a better understanding of biodiversity and the correct biological delimitation of numerous species complexes that include taxonomic and nomenclatural inconsistencies (Neustupa et al. 2010(Neustupa et al. , 2014Nemjová et al. 2011). The present results will also be of interest for taxonomical, nomenclatural and ecological studies, including metabarcoding approaches. ...
The taxonomy and nomenclature of Micrasterias arcuata are very problematic because of a wide morphological variation and the large number of poorly circumscribed infraspecific taxa. This study aimed at evaluating the phylogenetic position of strains traditionally assigned to M. arcuata based on molecular and phylogenetic approaches, and morphometric analyses. Multigene analyses were performed using the nuclear SSU rDNA and both chloroplast rbcL and psaA markers. Genetic analyses revealed that all three investigated strains of M. arcuata formed reasonably well-supported lineages, separate from all species of the core Micrasterias lineage and closely related to the Euastrum 2 lineage. Morphometric analyses exhibited differences among strains revealing important trends for morphological differentiation and delimitation of infraspecific taxa assigned to M. arcuata. All three investigated strains are separated by their morphological features and represent different taxonomic entities from the molecular and phylogenetic points of view. Available data support the proposal of Pseudomicrasterias gen. nov. within the family Desmidiaceae. One infraspecific taxon is erected to species level and classified as new combination of Pseudomicrasterias, and two new species are recognized.
... Notably, 5 of the studied taxa have been treated as subspecies in traditional taxonomic monographs (Růžička, 1981). However, published phylogenetic data clearly illustrated that these taxa form well-delimited species-level evolutionary units within the genus Micrasterias (Nemjová et al., 2011;Škaloud et al., 2011;Neustupa, Stastny & Škaloud, 2014). Therefore, in our analses we treated these taxa as separate units. ...
... The opposite pattern was only typical for M. semiradiata, which was the only species occupying the negative parts of PC1 in the morphospace illustrating the asymmetric variation between the terminal lobules of ULS (Fig. 3D). The ML and MP phylogenetic analyses yielded topologies that were very similar to the previously reported multigenic trees of the Micrasterias lineage (Škaloud et al., 2011;Neustupa, Stastny & Škaloud, 2014). The firmly supported clade ''A'', including the species complex of M. truncata, M. furcata (the type species of the genus) and several other taxa, proved to be in a sister position to the remaining clades (Fig. S1). ...
Green microalgae of the Micrasterias lineage are unicellular microorganisms with modular morphology consisting of successively differentiated lobes. Due to their morphological diversity and peculiar morphogenesis, these species are important model systems for studies of cytomorphogenesis and cellular plasticity. Interestingly, the phylogenetic structure of the Micrasterias lineage and most other Desmidiales is poorly related to the traditional morphological characters used for delimitation of taxa. In this study, we focused on symmetry breaking between adjacent cellular lobes in relation to phylogeny of the studied species. While pronounced morphological asymmetry between the adjacent lobes is typical for some species, others have been characterized by the almost identical morphologies of these structures. We asked whether there is any detectable average shape asymmetry between the pairs of lobes and terminal lobules in 19 Micrasterias species representing all major clades of this desmidiacean lineage. Then, we evaluated whether the asymmetric patterns among species are phylogenetically structured. The analyses showed that the phylogeny was in fact strongly related to the patterns of morphological asymmetry between the adjacent cellular lobes. Thus, evolution of the asymmetric development between the adjacent lobes proved to be the key event differentiating cellular shape patterns of Micrasterias . Conversely, the phylogeny was only weakly related to asymmetry between the pairs of terminal lobules. The subsequent analyses of the phylogenetic morphological integration showed that individual hierarchical levels of cellular morphology were only weakly coordinated with regard to asymmetric variation among species. This finding indicates that evolutionary differentiation of morphogenetic processes leading to symmetry breaking may be relatively independent at different branching levels. Such modularity is probably the key to the evolvability of cellular shapes, leading to the extraordinary morphological diversity of these intriguing microalgae.
... The palynomorphs are mainly composed of a dense aggregation of freshwater green algal remains, Micrasterias sp. (Neustupa, Šťastny', & Škaloud, 2014) clearly indicating that the depositional environment of the area changed from ca. 1,800 years ago to the present day. The area approximately 1 km south of the Pran Buri River (Figure 3a) began at ca. 1,800 years B.P. with a stagnant freshwater pond, suitable for photosynthesis by freshwater green algae dominated by Micrasterias, in an open, lowland forest environment. ...
A 370 cm long sedimentary core was investigated using paleoecological proxies to reconstruct environmental changes of the meander bend in Pak Nam Pran area, the Malay-Thai Peninsula during the last millenniums. The sedimentary profile can be divided into four biozones based on their dominant palynomorphs. The Micrasterias zone represents a back swamp on the floodplain deposited around 1800 years before present (B.P.) until 1,500 years B.P. After that, the younger Ilex zone represents a swampy area with Ilex trees until 1,000 years B.P. The younger Cyclotella striata zone represents the swampy area near the Pran Buri riverbank up to 150 years B.P. indicating an ongoing marine regression during the last millennium. The youngest Rhizophoraceae zone indicates a mangrove forest occurring from 150 years B.P. with seawater intrusions during daily high tides. Moreover, recent human activities are also recorded within the area indicated by strongly enhanced elements at the top of the core.
... The studied dataset comprised 68 mature cells taken from CAUP K608, a clonal strain of Micrasterias compereana. This strain, which has been used as a holotype for the taxonomic description of the species by Neustupa et al. [46], was originally isolated in 2011 from oligotrophic peaty pools near Étang Hardy, Aquitaine, France (43°43′ 08.60″N, 01°22′09.42″W). It was cultivated in 250 ml Erlenmeyer flasks with approximately 125 ml of the MESbuffered DY IV liquid medium at 22°C and illuminated at 40 μmol photons m −2 s −1 with 18 W cool fluorescent tubes (Philips TLD 18 W/33), at a light:dark (L:D) regime of 12:12 h. ...
Background
Unicellular green algae of the genus Micrasterias (Desmidiales) have complex cells with multiple lobes and indentations, and therefore, they are considered model organisms for research on plant cell morphogenesis and variation. Micrasterias cells have a typical biradial symmetric arrangement and multiple terminal lobules. They are composed of two semicells that can be further differentiated into three structural components: the polar lobe and two lateral lobes. Experimental studies suggested that these cellular parts have specific evolutionary patterns and develop independently. In this study, different geometric morphometric methods were used to address whether the semicells of Micrasterias compereana are truly not integrated with regard to the covariation of their shape data. In addition, morphological integration within the semicells was studied to ascertain whether individual lobes constitute distinct units that may be considered as separate modules. In parallel, I sought to determine whether the main components of morphological asymmetry could highlight underlying cytomorphogenetic processes that could indicate preferred directions of variation, canalizing evolutionary changes in cellular morphology.
Results
Differentiation between opposite semicells constituted the most prominent subset of cellular asymmetry. The second important asymmetric pattern, recovered by the Procrustes ANOVA models, described differentiation between the adjacent lobules within the quadrants. Other asymmetric components proved to be relatively unimportant. Opposite semicells were shown to be completely independent of each other on the basis of the partial least squares analysis analyses. In addition, polar lobes were weakly integrated with adjacent lateral lobes. Conversely, higher covariance levels between the two lateral lobes of the same semicell indicated mutual interconnection and significant integration between these parts.
Conclusions
Micrasterias cells are composed of several successively disintegrated parts. These integration patterns concurred with presumed scenarios of morphological evolution within the lineage. In addition, asymmetric differentiation in the shape of the lobules involves two major patterns: asymmetry across the isthmus axis and among the adjacent lobules. Notably, asymmetry among the adjacent lobules may be related to evolutionary differentiation among species, but it may also point out developmental instability related to environmental factors.
Electronic supplementary material
The online version of this article (doi:10.1186/s12862-016-0855-1) contains supplementary material, which is available to authorized users.
Taxonomic, nomenclatural and distributional changes since the publication of the 2011 edition (reprinted 2021) of The Freshwater Algal Flora of the British Isles (“Flora”) are reviewed together with some changes overlooked earlier. Many of the more recent changes are a result of studies combining an analysis of morphological and DNA sequence data. Of the 473 changes reported most concern the Chlorophyta (131) and the Charophyta (156) followed by the Cyanobacteria (101), with most of the alterations to the Charophyta involving the desmids (136). Also included are 83 new additions to the British and Irish freshwater algal floras, including 20 overlooked in the Flora. Most of these additions are new records: four are newly described desmids and Synura hibernica (Ochrophyta, Chrysophyceae, Synurales) and Chlorococcum turfosum (Chlorophyta, Chlorophyceae, Chlamydomonadales) are also new. The new additions to Flora include information on locality, collector and publication source. Reference is made to discussions in the Flora giving reasons why some genera and species combinations were not accepted, particularly concerning the Cyanobacteria for which a relatively conservative approach had been adopted in the previous edition of the Flora.
Esta primera edición del material bibliográfico se cons-
tituye en resultado del desarrollo del primer trabajo de
investigación de Algas del Paraguay. Ahora mirando unos
nueve años atrás y cuando no sabía como dar los pasos
iniciales de esta investigación, sin contar con anteceden-
tes propios de nuestro medio, con solo unos pocos infor-
mes técnicos aislados y extraoficiales, apenas tenía expe-
riencia de campo para el muestreo y procesamiento de
muestras de agua para el estudio de algas microscópicas,
entonces cuando el panorama sólo se constituía de objeti-
vos ambiciosos que parecían estar lejanos a lograrlos, he
podido sobresalir enfocada en la necesidad de establecer
un registro taxonómico, una base para el área de ficología.
Hoy se puede decir que se han dado, pasos en otras líneas
de investigación con importantes aplicaciones científicas.
El Atlas hace especial énfasis en la identificación de las al-
gas del Paraguay por medio de la utilización de una clave
dicotómica de identificación de géneros algales. Además,
este volumen constituye el primer registro oficial de las es-
pecies de algas microscópicas del Paraguay. La mayor parte
de las especies esta identificada con la nominación bino-
mial según la nomenclatura botánica, muchas de ellas se
han podido identificar hasta su denominación de variedad.
Este material incluye detalles de los sitios de muestreo,
así como ilustraciones paisajísticas y vistas de diferentes
ángulos de unas 431 especies identificadas, no se inclu-
yen especies no identificadas (a estas las incluiremos en
una próxima edición). Del total de especies identificadas,
la mayor parte de la riqueza algal corresponde al grupo
de las Chlorophytas con 253 especies identificadas. En el
grupo de las Bacillariophytas se han identificado unas 117
especies; entre las Euglenophytas se determinaron 17 es-
pecies; mientras que fueron 42 las especies identificadas
en el grupo de las Cyanophytas y 1 en las Rhodophytas al
igual que en Dinophytas que también cuenta con 1 sola
especie representante.
Otro punto tratado en este volumen, es la metodología de
muestreo y los materiales necesarios para llevar a cabo un
trabajo de investigación taxonómica de algas. Un listado
de los sitios de muestreo en tablas dinámicas, donde ade-
más se muestran los diferentes grupos taxonómicos a los que pertenece cada especie.
Conjugates (Zygnematophyceae) represent the most species-rich (ca. 4000 spp) algal lineage within the Streptophyta. Studies using various molecular markers have placed the class as one of the crown groups in Streptophyta and even suggested a close relationship between the zygnematophycean algae and land plants. Phenotypic diversity complicates systematics of the class and the relationships between its taxa remain poorly understood. Molecular phylogenetic analyses have established a number of clades in the class and revealed a disagreement between the traditional taxonomic structure of Zygnematophyceae and the pattern of phylogenetic relationships between the class members. in this paper, an overview of recent advances in our understanding of the phylogeny and classification of conjugating green algae is presented, with emphasis on the major clades established in the class, the clades' structure and polyphyly of some genera. We describe the areas of conflict and agreement between molecular phylogeny and traditional morphology-based taxonomy and stress that phenotypic characters provide little evidence for inferring relationships between taxa even at low taxonomic levels.
An investigation has been made into the present occurrence and distribution of desmids in the French Auvergne. 27 samples from different habitats revealed the presence of 280 taxa belonging to 251 species, of which 120 had not previously been recorded from this region.
The number of taxa per sample varied from 2 to 118; especially the samples from mesotrophic lakes were very rich in desmid species. An annotated list with corresponding figures of the recognized taxa is presented, and previous reports relating to desmids from the study-area are discussed.
Morphological species of freshwater microalgae often have broad geographic distribution. However, traditional species concepts have been challenged by the results of molecular phylogenetic analyses that mostly indicate higher diversity than was previously recognized by purely morphological approaches. A degree of phenotypic differentiation or different geographic distribution of species defined by molecular data remains largely unknown. In this study, we analyzed a pair of well-known and widely distributed desmid species (Micrasterias fimbriata and M. rotata) and tested for their phylogenetic and morphological homogeneity as well as their geographic distribution. Geometric morphometric and morphological attributes of cells were used in combination with genetic analysis of the trnG
ucc
sequences of 30 strains isolated from a variety of European locations and obtained from culture collections. Micrasterias rotata proved to be phylogenetically homogenous across Europe while M. fimbriata turned out to be composed of two firmly delimited lineages, differing by molecular as well as by morphometric and morphological data. Published records of traditional M. fimbriata were also included in the classification discrimination analysis and were placed into the newly identified lineages upon comparison to the morphometric data collected from living material. Largely disparate geographic patterns were revealed within traditional M. fimbriata. One phylogenetic lineage is frequent in central and eastern Europe, but occurs also in the British Isles. A second lineage has been recorded in North America and in Western Europe, where its distribution is possibly limited to the west of the Rhine River. Interestingly, the morphometric analyses of the published records illustrated that the geographic differences have remained largely unchanged since the 1850s indicating a previously unknown distributional stability among microalgal species groups such as the desmids.
MrBayes 3 performs Bayesian phylogenetic analysis combining information from different data partitions or subsets evolving under different stochastic evolutionary models. This allows the user to analyze heterogeneous data sets consisting of different data types—e.g. morphological, nucleotide, and protein—and to explore a wide variety of structured models mixing partition-unique and shared parameters. The program employs MPI to parallelize Metropolis coupling on Macintosh or UNIX clusters.
Availability: http://morphbank.ebc.uu.se/mrbayes
Contact: fredrik.ronquist@ebc.uu.se
*
To whom correspondence should be addressed.
The Molecular Evolutionary Genetics Analysis (MEGA) software is a desktop application designed for comparative analysis of
homologous gene sequences either from multigene families or from different species with a special emphasis on inferring evolutionary
relationships and patterns of DNA and protein evolution. In addition to the tools for statistical analysis of data, MEGA provides
many convenient facilities for the assembly of sequence data sets from files or web-based repositories, and it includes tools
for visual presentation of the results obtained in the form of interactive phylogenetic trees and evolutionary distance matrices.
Here we discuss the motivation, design principles and priorities that have shaped the development of MEGA. We also discuss
how MEGA might evolve in the future to assist researchers in their growing need to analyze large data set using new computational
methods.
— We studied sequence variation in 16S rDNA in 204 individuals from 37 populations of the land snail Candidula unifasciata (Poiret 1801) across the core species range in France, Switzerland, and Germany. Phylogeographic, nested clade, and coalescence analyses were used to elucidate the species evolutionary history. The study revealed the presence of two major evolutionary lineages that evolved in separate refuges in southeast France as result of previous fragmentation during the Pleistocene. Applying a recent extension of the nested clade analysis (Templeton 2001), we inferred that range expansions along river valleys in independent corridors to the north led eventually to a secondary contact zone of the major clades around the Geneva Basin. There is evidence supporting the idea that the formation of the secondary contact zone and the colonization of Germany might be postglacial events. The phylogeographic history inferred for C. unifasciata differs from general biogeographic patterns of postglacial colonization previously identified for other taxa, and it might represent a common model for species with restricted dispersal.
The present work summarizes the current diversity, distribution and autecology of desmids found within the Czech Republic; the focus is on the occurrence and autecology of rare taxa. Data are based on the author's extensive sampling from 2003–2009, during work for both his master's degree, and currently, his Ph.D. dissertation. Over 1 400 samples were collected, from various types of wetland habitats ranging from eutrophic fishponds, diverse bogs and fens, to ephemeral pools and various aerophytic habitats. Altogether, 526 taxa of desmids (401 species) belonging to 27 genera were found, 80 of them newly described in the Czech Republic. In the present work, 169 rare or otherwise noteworthy taxa, belonging to the following genera: Mesotaenium (1), Netrium (1), Roya (2), Tortitaenia (1), Gonatozygon (2), Closterium (14), Haplotaenium (2), Pleurotaenium (3), Docidium (1), Actinotaenium (6), Euastrum (9), Micrasterias (7), Cosmarium (78), Xanthidium (7), Staurodesmus (4), Staurastrum (25), Cosmocladium (2), Sphaerozosma (2), Hyalotheca (1) and Desmidium (1) are depicted by line drawings and briefly discussed with regard to their ecology, taxonomy or distribution within the Czech Republic or Central Europe. In addition, SEM images are provided for 45 taxa, and, finally, a comprehensive table is included with indicative notations concerning all taxa found.
This paper presents the results of long-term research regarding algal biodiversity of the Sikhote-Alin biosphere reserve, Primorsky Region (Russian Far East). The algal flora is comprised of 675 species represented by 839 subspecific taxa from 7 divisions: Cyanophyta - 77 (91 including subspecific taxa); Euglenophyta - 18 (21); Chlorophyta - 84 (86); Streptophyta - 137 (169); Rhodophyta -3; Ochrophyta - 355 (468) : Diatomophyceae - 331 (444), Chrysophyceae - 6, Xanthophyceae - 16, Phaeophyceae - 2; Dinophyta -1. Algal floras of different reserve water bodies are described: brackish, Blagodatnoe Lake; shallow freshwater, Golubichnoe Lake; alpine, Solontsovskie Lakes; rapid cold-water, Serebryanka and Dzhigitovka Rivers; lowland, Kolumbe River. The taxonomic composition of algal flora has been analyzed. The differences between algal communities of lakes and rivers are described and rare species are noted. The algal flora of Sikhote-Alin biosphere reserve is currently the richest and most diverse algal flora among all of six reserves studied in the Primorsky Region.
We investigated twenty-six strains of Xanthidium antilopaeum Kütz. and seven strains of X. cristatum Ralfs isolated from various European localities or obtained from public culture collections. A combination of molecular, geometric morphometric, and morphological data were used to reveal the patterns of the phylogenetic and morphological differentiation of these taxonomically very compli-cated desmid taxa. The molecular data based on trnGucc and ITS rDNA sequences illustrated the monophyly of both the complexes, which indicated that their traditional morphology-based discriminative criteria, such as the different number of spines, may generally continue to be considered relevant. The single exception was X. antilopaeum var. basiornatum B. Eichler et Raciborski, which was positioned outside the X. antilopaeum/cristatum clade. The independent status of this taxon was also confirmed on the basis of the geometric morphometric data, so that we concluded that it probably represents a separate species. Within X. cristatum complex, the traditional varieties X. cristatum var. cristatum Ralfs, X. cristatum var. uncinatum Ralfs, and X. cristatum var. scrobiculatum Scott et Grönblad turned out to be separate taxa. Conversely, X. cristatum var. bituberculatum Lowe lacked any taxonomical value. Our data on X. antilopaeum illustrated extensive phylogenetic as well as phenotypic variability within this species complex. However, our data did not result in any unambiguous pattern that would allow sound taxonomic classification. Finally, we also found out that the morphologically peculiar Staurastrum tumidum Ralfs belongs to the genus Xanthidium based on the combined rbcL + cox III data set. Consequently, this species was formally transferred to this genus.
We investigated nine strains of the Micrasterias crux-melitensis (Ehrenb.) Hassall ex Ralfs and M. radians W. B. Turner species complex. A combination of molecular, morphological, and geometric morphometric data was used to reveal the patterns of their phenotypic and phylogenetic differentiation. The molecular data based on internal transcribed spacer (ITS) rDNA, glycine transfer RNA (trnGuuc) intron, and SSU rDNA sequences revealed three phylogenetic lineages. One of them comprised the six European and North American strains that were morphologically identified as M. crux-melitensis. Phenotypic data illustrated high morphological variability of strains within this genetically homogenous lineage that spanned several traditional infraspecific taxa, including strains corresponding to M. crux-melitensis var. janeira (Racib.) Grönblad and M. crux-melitensis var. superflua W. B. Turner, whose morphometric characteristics profoundly differed. Three strains of M. radians formed two separate phylogenetic lineages corresponding to traditional varieties M. radians var. evoluta (W. B. Turner) Willi Krieg. and M. radians var. bogoriensis (C. J. Bernard) G. S. West. The morphological types corresponding to the former variety have, so far, only been reported from Africa. Therefore, we cannot preclude that geographic isolation may play a role in species differentiation of relatively large freshwater protists, such as Micrasterias.
The conjugating green algae represent a lineage of charophyte green algae known for their structural diversity and unusual mode of sexual reproduction, conjugation. These algae are ubiquitous in freshwater environments, where they are often important primary producers, but few studies have investigated evolutionary relationships in a molecular systematic context. A 109-taxon data set consisting of three gene fragments (two from the chloroplast and one from the mitochondrial genome) was used to estimate the phylogeny of the genera of the conjugating green algae. Maximum likelihood (ML), maximum parsimony (MP), and Bayesian inference (BI) were used to estimate relationships from the 4,047 alignable nucleotides. This study confirmed the polyphyly of the Zygnemataceae and Mesotaeniaceae with respect to one another. The Peniaceae were determined to be paraphyletic, and two genera traditionally classified among the Zygnematales appear to belong to the lineage that gave rise to the Desmidiales. Six genera, Euastrum, Cosmarium, Cylindrocystis, Mesotaenium, Spondylosium, and Staurodesmus, were polyphyletic in this analysis. These findings have important implications for the evolution of structural characteristics in the group and will require some taxonomic changes. More work will be required to delineate lineages of Zygnematales in particular and to identify structural synapomorphies for some of the newly identified clades.
The morphological and molecular differentiation of the Micrasterias truncata (Corda) ex Bréb species complex was investigated. In total, 17 strains traditionally assigned to M. truncata were isolated from different European localities (Czech Republic, southwest France, Ireland), and obtained from public culture collections. In addition, strains of the morphologically similar species, M. decemdentata (Nägeli) W. Archer and M. zeylanica F. E. Fritsch, were also included. Molecular phylogenetic analysis based on trnGucc intron sequences revealed five well supported clades. Two Australian strains assigned to M. truncata var. pusilla G. S. West formed a lineage sister to M. zeylanica. This was evident from a concatenated phylogeny based on small subunit rDNA and trnGucc intron sequences. The isolated position of these strains was also illustrated by parallel landmark-based geometric morphometric analysis of cell shapes. The strains NIES 783 and NIES 784 probably represent a separate species. Particular analysis, including additional strains, is needed to resolve the relationship inside this lineage. The second phylogenetic lineage, containing two strains of M. truncata var. semiradiata (Kützing) Wolle, was also different from other strains on the basis of morphometric data. We suggest recognizing this variety as a separate species, Micrasterias semiradiata L.A. Brébisson ex F. T. Kützing. The remaining three clades formed a firmly supported group of the ‘core’M. truncata recognized by both molecular markers. However, neither any morphological, morphometric, nor geographical pattern was detected among members of these three clades. This pattern could be caused by a relatively recent origin of these lineages that may represent a sympatric, truly cryptic species. Strains attributable to traditional morphologically defined variety M. truncata var. neodamensis were nested within the ‘core’M. truncata.
Molecular phylogenetic analyses of 93 new and 198 non-redundant GenBank rbcL sequences of the family Desmidiaceae (Zygnematophyceae, Streptophyta) established 22 mostly highly supported clades, in addition to four non-supported lineages and eight single-taxon branches within the family. Nine novel clades and single-taxon branches were identified, suggesting that current taxon sampling has not reached saturation in the family. The highly polyphyletic nature of most desmid genera corroborated in this study using a large taxon set, calls for re-evaluation of the genus concept in the family Desmidiaceae that traditionally relied on features of cell morphology. Molecular phylogenetic data have shown that these morphological characters are highly homoplastic or plesiomorphic and thus cannot be used to delineate genera. The dramatic discrepancy between the currently practised systematic treatment of the family and the composition of the clades based on sequence comparisons requires emendation of almost all existing genera and description of a larger number of novel genera. The clades identified during this study provide a framework for the future emendation/description of genera in the Desmidiaceae.
Not available Biological Sciences, School of
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