No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Sexual reproduction in Schizostauron (Bacillariophyta) and a preliminary phylogeny of the genus
Abstract
The focus of this paper is the sexual reproduction and phylogeny of Schizostauron Grunow, which were studied using clonal cultures isolated from the Indian Ocean coast of Mozambique near Tofo and Bazaruto. Taxa of Schizostauron were characterized by light and electron microscopy and a phylogeny derived from three genes (rbcL, psbC and short subunit). Schizostauron was established in the second half of the 19th century, then forgotten, with its taxa included in Cocconeis or Achnanthes sensu lato. Schizostauron, together with Astartiella and perhaps also Kolbesia and Karayevia, seems to form a third lineage of monoraphid diatoms, which are related to biraphid diatoms belonging to the Stauroneidaceae and Parlibellus, but not to the two other lineages of monoraphids (Achnanthes and the Achnanthidiaceae-Cocconeidaceae group). In culture, size reduction was followed by release of gametes and auxosporulation in mixtures of clones. Despite some morphological differences, four clones from the Bazaruto population proved to be sexually compatible, one of the clones being sexually compatible with the three others. Before gametogenesis, cells gathered in groups of two to eight through active movement. Some groups of cells surrounded themselves by weakly visible mucilage. Reproduction was isogamous morphologically, and apparently also behaviourally. Growing auxospores were surrounded by the empty irregularly arranged frustules of parental cells. In numerous aspects the pattern of sexual reproduction of Schizostauron is similar to that of Achnanthes sensu stricto. The rbcL identity matrix (IDM) for sexually compatible clones ranged between 0.998 and 0.984. One clone derived from the Tofo population had an IDM below 0.900 and was sexually isolated from the remaining clones. A description of Schizostauron davidovichiorum sp. Nov. is provided.
... Strains were kept in a growth chamber (Biogenet, Józefów, Poland) with radiation [photosynthetically active radiation (PAR), 400-700 nm] of 100 µmol photons m −2 s −1 , a 12 h photoperiod and a temperature of 20 • C. Before mating, cultures were reinoculated periodically to maintain an exponential growth phase. Mating experiments methodology applied for S. trachyderma follows Davidovich et al. (2017). Before the mating experiments, strains were checked daily under LM for homothallic reproduction (sexual reproduction within a clone). ...
... The life cycle of Schizostauron representative was first studied by Davidovich et al. (2017), where sexual reproduction was successfully documented for S. kajotkei Dąbek, Górecka and Witkowski (referenced as Schizostauron sp. 1). Mating experiments presented here were successful only for S. trachyderma but not for S. rawaii. ...
... The recent studies on the phylogenetic position of Schizostauron consistently suggest its close relationship to monoraphid genera such as Astartiella, Madinithidium, Karayevia, and Kolbesia, all nested in Stauroneidaceae family clade and not related to other monoraphid genera such as Achnanthes or Cocconeis (Davidovich et al., 2017;Górecka et al., 2021). Our results describing characteristics of sexual reproduction in S. trachyderma support this, as S. kajotkei and S. trachyderma pattern of sexual reproduction shares similarities to Craticula spp. ...
The focus of this study was to determine the mating type of Schizostauron trachyderma and examine the relationship between cell size (life cycle), lipid droplet size, and lipid content among diatoms with similar cell dimensions. To accomplish that, we have chosen monoclonal cultures of two closely related diatom species, namely S. trachyderma and S. rawaii . In a series of experiments, we successfully induced sexual reproduction within S. trachyderma strains to reconstruct the whole cell cycle involving cells of the maximum (initial cells) and minimum viable size for a given species. The mating-type and sexual reproduction stages were described and documented. A unique experimental setting involved initial cell isolation and their lipid droplet examination using flow cytometry and confocal microscopy after Nile Red staining. The results of the series of experiments indicate correlations between cell size, the number of neutral lipids per cell, and the size of lipid droplets, suggesting that cell capacity for lipid accumulation is dependent on their position in the life cycle.
... As Grunow had not selected the generitype of Schizostauron, Ross (1963) lectotypified Schizostauron with S. reichardtianum as typus generis; therefore, in accordance with the International Code of Nomenclature (Turland et al. 2018), Schizostauron is a valid name. However, Schizostauron was regarded by Ross (1963) as synonym of Achnanthes due to similarities of morphological characters such as heterovalvy, extension in the RV central area and SV striation, and the ultrastructure of which was unknown in the pre-SEM era (see Riaux-Gobin et al. 2015, Davidovich et al. 2017. ...
... Molecular phylogenies have grouped several birapid genera in a clade with the Stauroneidaceae, such as Sternimirus, Parlibellus, Dorofeyukea, along with the fistula-bearing genera Fistulifera and Proschkinia, and the exclusively epizoic genus Tursiocola (Bruder and Medlin 2008, Witkowski et al. 2016, Frankovich et al. 2018, Nakov et al. 2018, Sabir et al. 2018, Kulikovskiy et al. 2019, Majewska et al. 2019, Kim et al. 2020. The DNA sequence TAXONOMY OF SCHIZOSTAURON AND ASTARTIELLA data also suggest that the Stauroneidaceae include a well-supported clade of monoraphid genera including Karayevia, Kolbesia, Madinithidium, Astartiella, and Schizostauron (Witkowski et al. 2016, Davidovich et al. 2017, Sabir et al. 2018, Kulikovskiy et al. 2019, Kim et al. 2020). ...
... Taxonomic comment: A detailed description of this taxon has been published under Schizostauron sp. 1 in Davidovich et al. (2017). However, here we provide a formal description of the species as S. kajotkei. ...
Presented here are new insights into the marine monoraphid diatom genera Schizostauron and Astartiella, based on molecular and morphological data, including descriptions of new species. Although no unambiguous morphological synapomorphies between the two genera are currently recognized, they are closely related by DNA sequence data. Heterovalvate frustules of Schizostauron are characterized by a bifid stauros on the raphe‐bearing valve and intricate areolate occlusions on the sternum valve. In Astartiella, the raphe‐bearing valve is characterized by a process resembling a fistula by morphology, while the sternum valve presents a particular striation pattern. Observations by light and electron microscopy were made, along with a molecular phylogenetic analysis using a three gene (SSU, rbcL and psbC) concatenated dataset. Three new Schizostauron species are described (S. kajotkei, S. rawaii, S. papilliareae), and two new combinations proposed (S. citronella & S. trachyderma) for species that were previously included either in Achnanthes and Cocconeis, respectively. Likewise, six new species of Astartiella (A. almalikii, A. bornmanii, A. chunlianlii, A. marksii, A. persica, A. wangii,) are described. Molecular results exclude Schizostauron and Astartiella from three clades of exclusively monoraphid diatoms, the Achnanthaceae, Cocconeidaceae and Achnanthidiaceae, instead placing them in the Stauroneidaceae. Morphological features of Schizostauron and Astartiella, such as the stauros, fistula and coaxial internal proximal raphe endings, are found in other genera in this clade, whereas the only common feature with monoraphid diatoms as whole group is the heterovalvy of frustules.
... Cox and Williams (2006) discussed the non-congruence of features for this genus derived from phylogenetic analysis of chloroplast and protoplast morphology and the systematic position proposed by Round et al. (1990). Ashworth et al. (2017) and Davidovich et al. (2017) first showed that two strains of Parlibellus hamulifer belong within the stauroneioid branch on the basis of ML molecular analyses. Here, we obtained the same results using ML and BI (Fig. 1). ...
... The small and weakly silicified genus Fistulifera is closely related to stauroneoid diatoms, and one available strain with a two-gene dataset was included in the stauroneioid clade, though with low statistical support. Davidovich et al. (2017) obtained the same result. The morphology and phylogenetic position of this genus (using just SSU rDNA) was discussed by Zgrundo et al. (2013). ...
... It has very delicate 182 frustules prone to dissolution as well as the presence of an isolated central pore (fistula), a raphe sternum internally, and uniseriate striae with small circular areolae covered internally by hymenes (Zgrundo et al. 2013). Davidovich et al. (2017) postulated that species in this genus have one chloroplast per cell based on the investigation by Matsumoto et al. (2014), who described a new marine species from this genus, Fistulifera solaris. However, Zgrundo et al. (2013) showed that the freshwater species of Fistulifera are characterized by the presence of two parietal chloroplasts lying along each side of the girdle or curved around the apices. ...
... Cox and Williams (2006) discussed the non-congruence of features for this genus derived from phylogenetic analysis of chloroplast and protoplast morphology and the systematic position proposed by Round et al. (1990). Ashworth et al. (2017) and Davidovich et al. (2017) first showed that two strains of Parlibellus hamulifer belong within the stauroneioid branch on the basis of ML molecular analyses. Here, we obtained the same results using ML and BI (Fig. 1). ...
... The small and weakly-silicified genus Fistulifera is closely related to stauroneoid diatoms, and one available strain with a two-gene dataset was included in the stauroneioid clade, though with low statistical support. Davidovich et al. (2017) obtained the same result. ...
... It has very delicate frustules prone to dissolution as well as the presence of an isolated central pore (fistula), a raphe sternum internally and uniseriate striae with small circular areolae covered internally by hymenes (Zgrundo et al. 2013). Davidovich et al. (2017) postulated that species in this genus have one chloroplast per cell ...
Type material of Navicula kotschyi was studied, and this species was transferred to Dorofeyukea gen. nov. as D. kotschyi comb. nov. Dorofeyukea was described on the basis of DNA sequence and morphological data. Additional species assigned to this genus that were previously included in Navicula include: D. ancisa comb. nov., D. grimmei comb. nov., D. ivatoensis comb. nov., D. orangiana comb. nov., D. rostellata comb. nov. & stat. nov., D. savannahiana comb. nov., D. tenuipunctata comb. nov. and D. texana comb. nov. All Dorofeyukea species share the same morphological features, including having a narrow stauroid fascia surrounded by 1‐3 irregularly shortened striae, uniseriate and weakly radiate striae, circular or rectangular puncta in the striae that are covered internally by dome‐shaped hymenes, presence of a pseudoseptum at each apex and absence of septa. Partial DNA sequences of SSU and rbcL loci show Dorofeuykae belongs to the clade of stauroneioid diatoms together with Stauroneis, Prestauroneis, Craticula, Karayevia, Madinithidium, Fistulifera, Parlibellus and, possibly, Schizostauron. A new species from the monoraphid genus Madinithidium, M. vietnamica sp. nov., was described based on valve and chloroplast morphology as well as DNA sequence data.
This article is protected by copyright. All rights reserved.
... Comments: The stria density is at the high end of the several different ranges given in the literature, but appears to match specimens from Guam identified as this species by Lobban (2015a). Comments: This species, which has been reported as A. citronella from Guam (Lobban et al., 2012) and Tahiti (Ricard, 1977), now falls into Schizostauron (Davidovich et al., 2017;Górecka et al., 2021), but we cannot tell from the LM if the Chuuk specimen belongs to S. trachyderma as proposed or to S. kajotkei Dabek, Górecka & Witkowski. The distinction is hard to pin down because while Davidovich et al. (2017) state that their Schizostauron sp.1 is very similar to S. trachyderma except for the latter having only 9.8-12.1 striae in 10 μm on the SV, in transferring trachyderma from Achnanthes to Schizostauron, Górecka et al. (2021) give the stria density as 10-17 (vs 10-14). ...
... Comments: This species, which has been reported as A. citronella from Guam (Lobban et al., 2012) and Tahiti (Ricard, 1977), now falls into Schizostauron (Davidovich et al., 2017;Górecka et al., 2021), but we cannot tell from the LM if the Chuuk specimen belongs to S. trachyderma as proposed or to S. kajotkei Dabek, Górecka & Witkowski. The distinction is hard to pin down because while Davidovich et al. (2017) state that their Schizostauron sp.1 is very similar to S. trachyderma except for the latter having only 9.8-12.1 striae in 10 μm on the SV, in transferring trachyderma from Achnanthes to Schizostauron, Górecka et al. (2021) give the stria density as 10-17 (vs 10-14). Even without that confusion, our cell, with 10 striae in 10 μm fits both. ...
The present study enhances knowledge of the biodiversity of diatoms in Chuuk, Micronesia following our 2018 study on the seaweed-associated diatoms. We collected planktonic samples of diatoms from five sites of reef flats using a 20 μm mesh net, and two samples of seaweeds with epiphytes by hand from an islet on the barrier reef. In addition, the seaweed-associated diatoms from our 2018 study were analysed using scanning electron microscopy. A total of 109 diatom taxa are documented in the present study. Of these, 70 species were from net samples, and 39 species from the seaweed-associated diatoms. Thirty-one species are newly recorded from Micronesian waters. Most taxa are benthic or tychoplanktonic; euplanktonic diatoms were rare. The occurrence of benthic diatoms from the water column might be related to the Chuuk environmental conditions which include shallow water, strong light intensity and high grazing pressure, to which benthic diatoms seem to be able to better adapt than planktonic diatoms.
... The genus is typical of temperate to tropical marine littoral zones. Species in this genus have often been misidentified as the monoraphid genera Achnanthes or Cocconeis and have a complicated taxonomic history, which includes the registration of invalid holotypes [1][2][3][4][5]. ...
... These studies have shown Schizostauron to be monophyletic and closely related to other monoraphid genera such as Astartiella, Madinithidium, Kolbesia, and Karayevia. However, these "stauroneid" monoraphid genera (so named because of the presence of Stauroneis Ehrenberg sensu stricto in the molecular clade) are not monophyletic with respect to the other monoraphid genera of the Achnanthaceae, Achnanthidiaceae, and Cocconeidaceae, suggesting that their monoraphid states evolved independently [4,5,17]. ...
We provide for the first time the complete plastid and mitochondrial genomes of a monoraphid diatom: Schizostauron trachyderma. The mitogenome is 41,957 bp in size and displays two group II introns in the cox1 gene. The 187,029 bp plastid genome features the typical quadripartite architecture of diatom genomes. It contains a group II intron in the petB gene that overlaps the large single-copy and the inverted repeat region. There is also a group IB4 intron encoding a putative LAGLIDADG homing endonuclease in the rnl gene. The multigene phylogenies conducted provide more evidence of the proximity between S. trachyderma and fistula-bearing species of biraphid diatoms.
... Our recent observations, illustrated in detail first by Riaux-Gobin et al. (2013), show that the fistula also occurs in one more genus: the monoraphid Astartiella (Moser et al. 1998). However, all sequenced strains of Astartiella fell outside of the Proschkinia and Fistulifera clade (Davidovich et al. 2017, Sabir et al. 2018, Majewska et al. 2019. In general, the fistula is constituted internally of a wart-like structure covered with a finely perforated membrane (hymen) and externally as an apically oriented slit positioned close to the central nodule on the valve primary side (Lange-Bertalot 1997, Zgrundo et al. 2013, Matsumoto et al. 2014. ...
... Our results agree with Gastineau et al. (2019) and Majewska et al. (2019) in showing that Proschkinia is sister to Fistulifera. This pair also shares a clade with the genera Craticula, Sternimirus, Stauroneis, Parlibellus, Astartiella, and Schizostauron, which agrees with the molecular phylogenies in Davidovich et al. (2017) and Sabir et al. (2018). Although Proschkinia and Fistulifera show such distinct differences in their gross morphology (large, fairly robust naviculoid cells, with structure usually resolvable by LM in Proschkinia and very small, delicately silicified cells in Fistulifera) they do share some characters such as the fistula. ...
Detailed morphological documentation is provided for established Proschkinia taxa, including the generitype, P. bulnheimii, and P. complanata, P. complanatula, P. complanatoides and P. hyalosirella, and six new species. All established taxa are characterized from original material from historical collections. The new species described in this paper – P. luticola, P. staurospeciosa, P. impar, P. modesta, P. fistulispectabilis and P. rosowskii – were isolated from the Western Pacific (Yellow Sea coast of Korea) and the Atlantic (Scottish and Texas coasts). Thorough documentation of the frustule, valve and protoplast architecture revealed the combination of characters diagnostic of the genus Proschkinia: a single lobed chloroplast, a broad girdle composed of U‐shaped, perforated bands, the position of the conopeate raphe‐sternum relative to the external and internal valve surface, and the presence of an occluded process through the valve, termed the “fistula”. Seven strains of Proschkinia were grown in culture and five of these were sequenced for nuclear ribosomal SSU and plastid‐encoded rbcL. Phylogenetic analysis recovered a clade of Proschkinia with Fistulifera, another fistula‐bearing diatom genus, and together these were sister to a clade formed of the Stauroneidaceae; in turn, all these were sister to a clade composed of Parlibellus and data from two monoraphid genera Astartiella and Schizostauron. Despite morphological similarities between Proschkinia and the Naviculaceae these two taxa are distant in our analysis. We document the variation in the morphology of Proschkinia, including significant variability in the fistula, suggesting that fistula ultrastructure might be one of the key features for species identification within the genus.
... paludosa increase in size by 1.5 times after leaving the gametangia. The increase in gamete size as a factor that contributes to the facilitation of syngamy has been described from Schizostauron Grunow [12]. The second mechanism that provides syngamy in E. cf. ...
... A polyphyletic position of the genus Cocconeis is considered, and the term Achnanthales (Order Achnanthales Silva, 1962), up to now treated as homogenous (De Stefano and Marino 2003;Le Cohu 2005) is here reconsidered, as previously addressed in several other studies (i.e., Cox 2006;Cox and Williams 2006;Kulikovskiy et al. 2016;Davidovich et al. 2017). ...
A small marine monoraphid diatom with a linear-elliptic shape and simple terminal raphe endings was present on Raivavae (South Pacific). Particularly due to its different stria structure on both valves, this taxon is here classified as Cocconeis. The new species was present on the rocky intertidal shore of the coral-reef lagoon, as an epiphyte on a turf. Cocconeis vaiamanuensis sp. nov. can be compared to some other monoraphids with a simple raphe system and a rod-like shape. The new taxon has small marginal processes on the sternum valve (SV) mantle, as previously reported for Cocconeis peltoides. Such processes were also previously observed in Platessa and Psammothidium. A cladistic analysis based on ultrastructure shows an affiliation between several close-by taxa. Cocconeis of the C. peltoides section are close to Psammothidium, whereas other Cocconeis without processes are closer to Platessa and Achnanthidium. A clone of Cocconeis cf. sigillata (SZCZCH1200) allowed for a molecular phylogeny to be reconstructed. The molecular signature of Cocconeis cf. sigillata is close to that of Lemnicola hungarica. Cocconeis is a genus with different and complex morphologies that may be split into independent clades (genera). The SV processes may be a vestigial character reminiscent of an ancestral state.
... Stephanopyxis, Paralia and Hyalodiscus (Ashworth et al. 2012) share a very regular quincunx perforation pattern of the basal silica layer, irrespective of the very different microarchitecture of their completed valves (Kaczmarska and Ehrman 2015). In other species, molecularly unrelated diatoms may possess convincingly similar overall final valve morphology (Davidovich et al. 2017a;Kociolek et al. 2019). This suggests that at least the early stages of their valve ontogenesis may differ. ...
The traditional taxonomic affiliation of the diatom Ardissonea crystallina has been recently questioned, as it exhibits a mixture of polar centric and araphid pennate characters. Overall valve architecture and mode of sexual reproduction suggest araphid pennates are its closest relatives. On the other hand, recovered molecular phylogenies consistently place it among the polar centrics. Our investigation of the earliest stages of valve morphogenesis, formation of the basal silica layer, adds to the argument that A. crystallina is indeed a polar centric diatom. We compared developmental stages in A. crystallina to unequivocally centric diatoms (non-polar Hyalodiscus stelliger and polar Biddulphia tridens) and published literature for araphid pennates and determined that A. crystallina has evolved a thus far unique mode of valve development. The significance of valve morphogenesis in better understanding diatom evolution and diversification is discussed.
... A number of species have two gametes formed in each gametangial cell with one of them being active, while another is passive. This points at trans-anisogamy as in the case of, e.g., Schizostauron Grunow [17]. ...
... paludosa increase in size by 1.5 times after leaving the gametangia. The increase in gamete size as a factor that contributes to the facilitation of syngamy has been described from Schizostauron Grunow [12]. The second mechanism that provides syngamy in E. cf. ...
Sexual reproduction and the life cycle of the marine pennate diatom Entomoneis cf. paludosa are described. The reproduction in this species is characterized by morphological and behavioral isogamy. Two gametangia are involved in the sexual process, each of which produces two gametes.
... S1) indicates that the diatoms known to exhibit multi-step auxosporulation are not restricted to a single lineage (the Thalassiosirales, Coscinodiscales and Melosirales are not sister groups), showing that it cannot be assumed that either this type of life cycle, or the stricter 'orthodox' type of life cycle reported by von colleagues (von Stosch 1951, 1956;von Stosch & Drebes 1964;von Stosch et al. 1973), is the prevalent one. Chepurnov et al. (2006) reported a further interesting phenomenon in Thalassiosira weissflogii, which may give hints as to how the isogamy of pennate diatoms (and that of the anomalous centric diatom Ardissonea: Davidovich et al. 2017b) may have arisen. This was the observation that the egg cells of T. weissflogii are capable of amoeboid movement: adjacent oogonia were seen to interact, the egg cell of one pushing inside the frustule of the other. ...
This chapter contains sections titled:IntroductionCentric DiatomsPennate Diatom Life Cycles and ReproductionAuxospore Development and StructureInduction of Sexual ReproductionAcknowledgments
The monograph concerns items related to reproductive biology of diatoms including such sections as sex and principles of sex determination in diatoms, their life cycles, patterns of sexual reproduction, sex distribution and mating systems, factors inducing sexual reproduction, inheritance coupled with sex, reproductive boundaries and distribution of diatoms, phylogeny of diatoms in the light of reproductive characteristics, etc. The book is dedicated for specialists in algology, hydrobiolody, reproductive biology; for students and graduate students in the relevant areas of study. (in Russian)
During a survey of benthic diatoms from the coral reefs of the Indian Ocean (Scattered
Islands) and Pacific Ocean (Tuamotu Archipelago), an interesting monoraphid diatom
was observed and examined by light microscopy and various electron microscopy
methods including Focus Ion Beam milling. Our thorough analysis revealed the
similarity of this diatom to Bennettella R.W.Holmes, which we reference in the name:
Xenobennettella Witkowski & Riaux-Gobin gen. nov., with Xenobennettella coralliensis
Witkowski & Riaux-Gobin sp. nov. as the generitype. The type habitat for this new
species is the sublittoral coral reef of Juan de Nova in the Mozambique Channel.
The sternum valve of the new genus is characterized by an alveolate ultrastructure
with the rim of the alveola opening along the valve margin, resembling the sternum
valve of Bennettella. Internally, Xenobennettella differs from the latter by possessing
a cavum (horseshoe-shaped chamber) on one side of the valve, in a central axial
position. The raphe valve of Xenobennettella has small, marginal, apically elongate
chambers, which are internally delineated by transapical ribs that are very similar
to Bennettella. However, the raphe in the new genus is different from the latter,
resembling some Cocconeis and Planothidium with internal raphe endings bent in the
opposite direction, while resembling some Planothidium taxa externally by ending on
the apical part of the mantle. This contrasts to Bennettella, which has a unique raphe
system, with external raphe endings below the apices, a prominent axial structure and
a transapically expanded central area. Likewise, the external surface of Bennettella is
different from that of the new genus with a complex mantle structure and biseriate
striae. In Xenobennettella, the valve mantle of the raphe valve is simple and perforated
by areola. The transapical striae occur in the valve margin and the axial area is
ornamented along its course with a single row of densely packed areola on both sides.
The characteristics of the raphe valve and alveolate sternum valve place the new genus
among the Achnanthidiaceae.
A new monoraphid diatom species from the genus Karayevia sensu lato (Bacillariophyceae: Stauroneidaceae) with remarks on taxonomy and phylogeny of the genus, Diatom Research, A new monoraphid diatom, Karayevia chelonica sp. nov., is described from Nha Trang, Vietnam, isolated from marine littoral habitats. Phylogenetic analysis based on partial 18S rDNA and rbcL sequences places this species within the family Stauroneidaceae, and related to other monoraphid species. Karayevia chelonica sp. nov. differs from other species in the genus in stria density and a broad axial area on the rapheless valve. Morphology and taxonomy of the closely related genera Karayevia, Kolbesia and Madinithidium are discussed. Based on morphological characteristics, we conclude that these three genera might represent a single genus, however, further molecular investigation is required to clarify their taxonomic and systematic affinities.
In many marine littoral and sublittoral benthic habitats, we find small diatoms with few features resolvable with light microscopy (LM) other than internal costae across their valves. While classically those internal costae have defined their identification and classification, the use of electron microscopy and of molecular data have started to reveal the true diversity of unrelated forms and genera (e.g., Anaulus, Eunotogramma, Hustedtiella, or Plagiogramma) which possess these structures. Here we describe the new genus Ambo, in an attempt to clarify some of the polyphyly of taxa with internal costa by formally transferring Anaulus balticus, Anaulus simonsenii, and Plagiogramma tenuissimum as well as Ambo gallaeciae, described here. Related to this, we attempt to document and characterize the genus Anaulus itself, which was formally described by Ehrenberg with an illustration. A search by LM of mica designated by Ehrenberg as the holotype of Anaulus scalaris, the generitype of Anaulus, failed to recover a specimen which adequately describes the genus to the exclusion of other genera with internal costa. We also present morphological and molecular data for Anaulus creticus and suggest a new genus—Ceratanaulus—to reflect the distinct morphological and molecular characters we documented.
Madagascar is an isolated oceanic island characterized by high degrees of endemism at all taxonomic levels. The waters surrounding Madagascar are still poorly studied for benthic marine diatom assemblages. The aim of our study was to analyse the taxonomic biodiversity and molecular phylogeny of the diatom assemblages of the Nosy Be archipelago in terms of their ubiquity/rarity. A total of 65 samples from 14 sampling sites were collected from the Nosy Be and Nosy Tanikely islands in June/July 2014. Diatom identification, based on light and electron microscopic examination, revealed 332 diatom taxa. From those, ∼90 strains were isolated and successfully cultured. So far, DNA has been extracted and one chloroplast gene (rbcL) sequenced from 21 strains in order to reconstruct their single gene phylogeny. Taxa selected for sequencing and the preliminary phylogeny are from genera considered common benthic and planktonic forms in the marine littoral: Bellerochea, Melosira, Paralia, Triceratium, Navicula, Hippodonta, Auricula, Nitzschia, Cocconeis, and some araphids. For each site, Shannon and Simpson biodiversity indices were calculated. Diatom assemblages of Nosy Be were characterized by high biodiversity. The most abundant species was Cocconeis scutellum. Whereas some of the cultured taxa seem to represent cosmopolitan or zonal forms: e.g., Bellerochea malleus, Triceratium dubium, Melosira lineata, Paralia crawfordii, or Nitzschia inconspicua, most of the taxa isolated in culture and sequenced have not been observed in earlier works based on use of molecular markers. The dominant taxa were generally those with broad geographic distribution with global/Indo-Pacific affinities. Amongst all 332 taxa, only 35% have been identified to the species level. Many of the taxa identified to the generic level may turn out to represent taxa new to science after further SEM examination and DNA sequencing.
A listing of the accepted freshwater diatom genera worldwide is presented, indicating the distribution of the genera by continent. Out of a total of 249 genera, 63 (25%) of those genera are endemic to a single continent. The continent with the largest number of endemic genera is Asia, hosting 35 endemic genera. While Asia is also the continent with the most reported genera, a regression analysis showed there is no relationship between the continental richness of genera and generic endemism. Disjunct genera, those found on two continents, represent distributions found in other groups of organisms such as in higher plants, including North America-Europe, North America-Asia and Southern Hemisphere disjunctions. There are certain lineages of freshwater diatoms where the endemic genera are restricted to specific continents: both thalassiosiroid and cymbelloid diatoms have endemics in Asia, while eunotioids have endemics in South America. Future research is suggested combining distributions over space and time related to phylogenetic relationships of diatoms.
we present light and scanning electron microscopic observations on the valve ultrastructure of 4 species of the genus Ger-mainiella from the Maolan Nature Reserve from guizhou Province, China. This is the first report of the genus from China. The new species differ in the shape and size of the valves, but they all have the large conopeum covering the entire face of the valve. one species, G. sinica, lacks small tubules running perpendicular to the raphe opening, one of the defining features of the genus, and in having the large conopeum but lacking the tubules resembles another diatom, Fallacia emmae, described from the subantarctic region. we suggest the possibility that other species assigned to Fallacia may be closely related to Ger-mainiella. a new combination, G. emmae, is proposed. we discuss the nature of conopea, and other small, finely-structured naviculoid diatoms that might be better placed in Germainiella. The genus is now recognized to have a total of 8 species, 4 of which are from the Maolan Nature Reserve.
Until now only one group of diatoms, the Bacillariaceae, was known to contain heterotrophic representatives. We show that a second group, represented by species in the genus Tursiocola, has undergone evolutionary loss of photosynthesis within the Bacillariophyta. Heterotrophy was evidenced by the presence of only apochlorotic cells in live and motile specimens. Three species of Tursiocola (T. bondei sp. nov., T. alata sp. nov., and T. gracilis sp. nov.), of which at least two are apochlorotic, are described as new to science from the skin of Florida manatees. T. ziemanii and T. varicopulifera were also observed to be apochlorotic. A new morphological feature termed a “fastigium” was observed on some Tursiocola spp. and is described as an extension of the mantle margin at the valve apex that overhangs the apex and extends towards the valve face. The presence of greatly elevated marginal ridges on the valve face of T. alata sp. nov. is a newly observed morphological character within the genus. Phylogenetic analyses using ribosomal RNA sequences indicate that Tursiocola is monophyletic, though morphological character analysis suggests paraphyly as species of the closely related Epiphalaina genus are embedded within a larger Tursiocola clade.
Diatoms are important contributors to the benthic microeukaryote flora. This manuscript lays the foundation for future metagenomic and environmental sequencing projects off coastal China by curating diatom DNA sequences from the Yantai region of the Bohai and Yellow Seas (Northeast China). These studies are based on cultures established from samples collected in different seasons from marine littoral and supralittoral zones in 2013 and 2014. Thirty-six diatom strains were cultured successfully and identification of these clones was determined by light and scanning electron microscopy(LM and SEM) and DNA sequencing of the nuclear-encoded small subunit ribosomal RNA (SSU)and chloroplast-encoded rbcL and psbC genes. The strains primarily represent raphid pennate genera, such as Amphora, Amphora (Oxyamphora), Caloneis, Diploneis, Halamphora, Navicula, Nitzschia, Parlibellus, Pleurosigma, Surirella and Tryblionella. When the DNA markers from these strains were analysed in a multi-gene phylogeny, we found that some clones-particularly within the genera Amphora, Navicula and Nitzschia-show greater than expected genetic diversity despite their very similar morphology and morphometrics. We also compared the molecular and morphological identities of several seemingly ubiquitous marine littoral taxa in the genera Amphora and Nitzschia from the Indian Ocean and Atlantic Ocean, the Red Sea and Adriatic Sea to their Yellow Sea counterparts.
Over the years, many reviews of different aspects of diatom biology, ecology and evolution have appeared. Since 1993 many molecular trees have been produced to infer diatom phylogeny. In 2004, Medlin & Kaczmarska revised the systematics of the diatoms based on more than 20 years of consistent recovery of two major clades of diatoms that did not correspond to a traditional concept of centrics and pennates and established three classes of diatoms: Clade 1 = Coscinodiscophyceae (radial centrics) and Clade 2 = Mediophyceae (polar centrics radial Thalassiosirales) and Bacillariophyceae (pennates). However, under certain analytical conditions, an alternative view of diatom evolution, a grades of clades, has been recovered that suggests a gradual evolution from centric to pennate symmetry. These two schemes of diatom evolution are evaluated in terms of whether or not the criteria advocated by Medlin & Kaczmarska that should be met to recover monophyletic classes have been used. The monophyly of the three diatom classes can only be achieved if (1) a secondary structure of the small subunit (SSU) rRNA gene was used to construct the alignment and not an alignment based on primary structure and (2) multiple outgroups were used. These requirements have not been met in each study of diatom evolution; hence, the grade of clades, which is useful in reconstructing the sequence of evolution, is not useful for accepting the new classification of the diatoms. Evidence for how these two factors affect the recovery of the three monophyletic classes is reviewed here. The three classes have been defined by clear morphological differences primarily based on gametangia and auxospore ontogeny and envelope structure, the presence or absence of a structure (tube process or sternum) associated with the annulus and the location of the cribrum in those genera with loculate areolae. New evidence supporting the three clades is reviewed. Other features of the cell are examined to determine whether they can also be used to support the monophyly of the three classes.
This paper proposes a new monoraphid genus Gliwiczia Kulikovskiy, Lange-Bertalot & Witkowski, separated from Achnanthes sensu lato. Here we describe four species G. skvortzowii Kulikovskiy, Lange-Bertalot & Witkowski, G. tenuis Kulikovskiy, Lange-Bertalot & Witkowski, G. latarea Kulikovskiy, Lange-Bertalot & Witkowski and G. vixcalcar Kulikovskiy, Lange-Bertalot & Witkowski which all are new to science. In terms of morphology, this group of species closely resembles Achnanthes calcar Cleve. Also proposed is the taxonomic transfer of A. calcar Cleve to Gliwiczia calcar (Cleve) Kulikovskiy, Lange-Bertalot & Witkowski comb. nov. Our taxonomic conclusions about the position of this group of species is based on light microscopic (LM) examination of the type material of A. calcar and on extensive LM and scanning electron microscopic (SEM) studies on material originating from Lake Baikal. This new genus differs from other established monoraphid genera in the of cavum (horse shoe) present on both raphe and sternums valves, uniseriate striae on both valves, and areola occlusions in a form of open circular foramina externally. The raphe valve is only slightly concave, whereas the sternum valves appear flat. Only one of the species belonging in Gliwiczia gen. nov., G. c a l c a r, is known to inhabit oligotrophic and dystrophic freshwater lakes of Eurasia. It seems highly likely that the newly described species are limited in their distribution to the waters of Lake Baikal. None of them have thus far been illustrated in any accessible literature even under provisional names.
Several diatoms in the family Achnanthaceae (Bacillariophyta), mainly from marine environments, have species with strongly apiculate, lemon-shaped valves. Some of them originally described under the genus Cocconeis (i.e., C. trachyderma or C. citronella), while others were first described as Stauroneis species [i.e. Stauroneis apiculata or S.(?) obesa]. Afterwards, Cocconeis citronella has been recombined within Achnanthes by Hustedt. The type material of C. citronella from Albert Mann’s collection, housed in the Smithsonian Institution (US), has been examined with light microscope; some ambiguities are pointed out and new details added to the original description. The intricate history of the latter taxon is redrawn and comparison with allied taxa are tentatively addressed. Cocconeis trachyderma is lectotypified and recombined as Achnanthes trachyderma comb. nov. Stauroneis apiculata and S.(?) obesa are recombined as Achnanthes apiculata comb. nov. and Achnanthes obesa comb. nov. respectively. The examination with light and scanning electron microscope of several marine samples from the Society Archipelago details the unique morphology of Achnanthes trachyderma which, until recently, has been often misidentified as Achnanthes citronella due to certain similarities between both taxa.
New areola types - macroareola and postmacroareola are described. On the basis of fine structure and taking into consideration new areolae types, an emended description of the genus Karayevia Round & Bukhtiyarova is presented and reasoning given for subsuming the genus Kolbesia Round
& Bukhtiyarova within Karayevia. Comparative morphological analyses of nine Karayevia species has
resulted in ideas concerning the evolution of the genus. The new combination Karayevia nitidiformis
(Lange-Bertalot) Bukhtiyarova comb. nov. is formally proposed and a validation is given for the new
combinations Karayevia amoena (Hustedt) Bukhtiyarova comb. nov. and Karayevia submarina
(Hustedt) Bukhtiyarova comb. nov.
We studied a group of monoraphid diatom species (Bacillariophyceae, Achnanthidiaceae) found in the marine coastal environment of tropical islands of the Caribbean Sea, western Atlantic Ocean, Indian Ocean, South Pacific Ocean, the Adriatic Sea and the Black Sea. Based on light and electron microscope examination, Madinithidium was formally described as a genus new to science with the generitype defined as Madinithidium undulatum. The characteristic features of the valve structure are a strongly developed sternum and raphe sternum, transapical striae formed by a single areola (macroareolae) positioned in small depressions, elevated virgae and coaxial internal central raphe endings. Furthermore, the striae of both raphe and sternum valves are closed by finely perforated hymenes. Madinithidium and Achnanthidium species are difficult to identify correctly with light microscopy since their valves are small and finely structured. Four species recently described from the western Indian Ocean and assigned to Achnanthidium sensu lato - Achnanthidium capitatum, A. flexuistriatum, A. pseudodelicatissimum and A. scalariforme - possessed morphological features permitting their placement into Madinithidium gen. nov. The above-mentioned species were formally transferred to the new genus.
Here we present a formal description of Biremis panamae Barka, Witkowski et Weisenborn sp. nov., which was isolated from the marine littoral environment of the Pacific Ocean coast of Panama. The description is based on morphology (light and electron microscopy) and the rbcL, psbC and SSU sequences of one clone of this species. The new species is included in Biremis due to its morphological features; i.e. two marginal rows of foramina, chambered striae, and girdle composed of numerous punctate copulae. The new species also possesses a striated valve face which is not seen in most known representatives of marine littoral Biremis species. In this study we also present the relationship of Biremis to other taxa using morphology, DNA sequence data and observations of auxosporulation. Our results based on these three sources point to an evolutionary relationship between Biremis, Neidium and Scoliopleura. The unusual silicified incunabular caps present in them are known otherwise only in Muelleria, which is probably related to the Neidiaceae and Scoliotropidaceae. We also discuss the relationship between Biremis and the recently described Labellicula and Olifantiella.
Specimens of Fallacia tenera were collected from the surface sediment at in a river estuary in Japan. Auxosporulation occurred in a rough culture. Morphological structures of vegetative cells and auxospores were observed in detail. The vegetative cells have one H-shaped chloroplast. The striae were interrupted by two depressed lateral sterna internally and partly covered by a finely porous conopeum on the external surface. The lateral sterna and porous conopea formed two more or less curved longitudinal canals connecting with the exterior via opening pores on both sides of a terminal fissure. This combination of characteristics is unique to the genus Fallacia. The cingulum was composed of three bands, such as an open valvocupula and two comparatively thin pleurae. The two pleurae could be distinguished by the shape of their ligulae. The second band had a triangular ligula, whereas the ligula of the third band is arc-shaped. The auxosporulation was type IA1a in Geitler's classification. Two paired gametangia formed two anisogametes in each of them. Two auxospores formed in the thecae of the gametangia after a trans physiological anisogamy. The perizonium of the auxospore consisted of a set of transverse bands and five longitudinal bands. The primary transverse band was about twice wider than the secondary ones. The circular incunabular scales were present on the two terminals of the auxospore and on the surface of the primary transverse band. The primary longitudinal band had an acute terminal and was flanked by secondary longitudinal bands. Each side had two secondary longitudinal bands. All longitudinal bands were immediately beneath the transverse bands. Morphological comparison between Fallacia and Pseudofallaica, and the taxonomic position of F. tenera is also discussed.
The allogamous raphid diatom Achnanthes longipes C. A. Agardh possesses a complex breeding system involving interactions between three types of clone: monoecious, unisexual and bisexual. Previous studies showed that these three types can be crossed with each other, with a tendency for sexual characteristics to be inherited: inbred monoecious lineages gave rise to monoecious or, very rarely, to bisexual clones, while inbred unisexual lineages yielded unisexual and bisexual clones. The current paper reports on the progeny of crosses between monoecious and unisexual clones and their inbred offspring. All three types of clone appeared in the F1 and F2, although unisexual clones of opposite sex to the parental clone were not found. Inbreeding depression was observed and also a tendency for ‘normal’ auxosporulation (producing two auxospores per pair of gametangia) to be replaced by ‘reduced’ or ‘intermediate’ auxosporulation (producing one auxospore per pair). In addition, patterns of incompatibility were observed that were not seen during earlier studies of clones isolated directly from nature. These included the inability of some F1 clones to mate with each other, in spite of compatibility with all other clones examined (unisexual, bisexual and monoecious).
Sexual reproduction and mating system of the freshwater diatom Ulnaria ulna (Nitzsch) Compère were studied by using clonal cultures. Mating system of the species involves homo-and heterothallic modes of reproduction; and both male and female clones were capable of homothallic reproduction. Two types of gametogenesis corresponding to two mating types were investigated. Analysis of the crossing table, gamete morphology, and sex distribution in the progeny resulted from intraclonal reproduction provided evidences that anisogamy and two mating types were determined in U. ulna genetically; male and female clones were hetero-and homogametic correspondently. Specific active movement of male gametes caused by the formation and retraction of pseudopodia-like structures on the gam-ete surface was described. The absence of reproductive isolation between clones gathered from geographically distant populations suggests continuity and broad distribution of the species. K e y w o r d s : Ulnaria ulna, mating system, sexual reproduction, gametogenesis, gametes movement, reproductive isolation. Introduction Last three decades brought us numerous publications, which indicated hetero-thallic character of mating system in many pennate diatoms and others). Biparental sex distribution suggests clear strategy of breeding experiments in pair combination of clones. Surprisingly, in the be-ginning experiments with Ulnaria ulna we received unexpected results. Signs of auxosporulation, i.e. gametes, empty gametangial frustules, zygotes, young and growing auxospores, etc. were found almost in all pair cross combina-tions. However, careful investigation of the pattern of sexual reproduction allowed us revealing two types of gametogenesis and corresponding modes of gametes behaviour that elucidated mating system and mysterious "panmixia" of clones in this species. The strategy of fertilization in araphid sessile diatoms is fairly diverse. In some araphid species parental cells need to be lain down
Phylogenies are increasingly used in all fields of medical and biological research. Moreover, because of the next generation sequencing revolution, datasets used for conducting phylogenetic analyses grow at an unprecedented pace. RAxML (Randomized Axelerated Maximum Likelihood) is a popular program for phylogenetic analyses of large datasets under maximum likelihood. Since the last RAxML paper in 2006, it has been continuously maintained and extended to accommodate the increasingly growing input datasets and to serve the needs of the user community.
I present some of the most notable new features and extensions of RAxML, such as, a substantial extension of substitution models and supported data types, the introduction of SSE3, AVX, and AVX2 vector intrinsics, techniques for reducing the memory requirements of the code and a plethora of operations for conducting post-analyses on sets of trees. In addition, an up-to-date, 50 page user manual covering all new RAxML options is available.
The code is available under GNU GPL at https://github.com/stamatak/standard-RAxML.
Alexandros.Stamatakis@h-its.org.
Valve development has been examined in Achnanthes minutissima var. saprophila H. Kobayasi & Mayama. The formation of the raphid valve (RV) proceeds in the same sequence as has previously been described for Navicula. Early development of the araphid yalve (AV) is remarkably similar to that of the RV, in that a primary central rib and primordial central nodule are initiated, followed by the development of secondary arms from the centre and the recurring of the primary rib at the poles. Therefore raphe slits appear both at the centre and poles during the early development of the AV. However, thin fin-like depositions arise along the primary central rib between the secondary arms extending out from the centre and the centripetal extensions of the primary central rib recurring from the poles. The fins then fuse with the secondary arms and the in-turned primary central rib, so that the initially-formed raphe slits do not develop any further and are filled in: an axial area devoid of a raphe is thus formed. The valve ontogeny of this taxon suggests secondary reduction from the biraphid Naviculae.
Phylogenetic reconstructions of the diatoms have been inferred with the 18S and 16S ribosomal RNA genes. Previous studies have shown that the group is divided into two major clades, with support coming initially from the arrangement of the Golgi bodies inside the cells in extant taxa. Features of extinct taxa that also support these clades can be found in the earliest fossil record of the diatoms and include the presence or absence of a central structure in the valve wall and the type of peripheral linking mechanisms between cells. Here we demonstrate that the general pattern of the auxospore expansion and the structure of their walls, the structure of the pyrenoid and the ultrastructure of the spermatozoid further support the molecular clades. Given the combined molecular and morphological support, we propose two new subdivisions (Coscinod-iscophytina and Bacillariophytina), emend the classes Coscinodiscophyceae and Bacillariophyceae and propose a new class, the Mediophyceae for the bipolar centrics and the Thalassiosirales.
The identity of a small-celled diatom Naviculadicta pseudofallacia Witkowski, Metzeltin et Lange- Bertalot, originally described from Bear Island, southernmost island of the Norwegian archipelago Svalbard, is reconsidered. Observations of marine samples from the Kerguelen archipelago (Southern Ocean, Indian Ocean sector) revealed that this species also occurs in the Subantarctic region. The original classification within Naviculadicta was erroneous since this species is a monoraphid taxon and belongs to the Achnanthales. Its morphological features justify creating a new genus Scalariella Riaux-Gobin, which is distinguished from other achnanthoid genera by a peculiar raphe system, the stria structure of the sternum valve (each stria composed of a depressed macroareola), and the presence of a lateral solid area in the raphe valve, splitting each stria into two areolae. Based on light and electron microscopy, N. pseudofallacia is renamed Scalariella pseudofallacia (Witkowski, Metzeltin et Lange-Bertalot) Riaux-Gobin et Witkowski comb. nov. The genus also includes a second and rare species, observed in the Kerguelen material, S. oblongella Riaux-Gobin, Witkowski et Ruppel, which is described and illustrated, but which needs complementary observations. The morphology of Scalariella is compared to that of some genera split from the genus Achnanthes Bory. The biogeography of Scalariella pseudofallacia, a marine taxon probably misidentified in the past due to its small size, is reconsidered with respect to its affinity for subpolar, cold water habitats, in both hemispheres.
As part of a larger study to reconstruct evolutionary relationships within the naviculoid diatoms, phylogenetic analyses of several freshwater naviculoid species were performed using three different genes (SSU rRNA gene, LSU rRNA gene and rbcL gene), and the morphology of the sequenced species was investigated. This study focused on species of Placoneis, a genus that was separated from Navicula based on its chloroplast morphology, a feature that places it within the Cymbellales. The phylogenetic analyses also clearly place Placoneis in this order, but the relationships between the different genera varied with different genes. Navicula hambergii, whose allocation to Navicula sensu stricto was known to be wrong, is shown to belong to the genus Placoneis and is transferred to that genus. Its transfer is supported by both the phylogenetic analyses and the morphological investigation.
A molecular analysis of 91 species of naviculoid diatoms representing 22 genera and 72 species using three different molecular markers was performed. Support was found for many groups established by traditional morphological methods. Gomphonema, Cymbella, and Encyonema were recovered as monophyletic groups. Cymbelloid diatoms were divided into two clades, which corresponded to the genera of Cymbella and Cymbopleura. Gomphonema was also divided into two groups based on external areolae coverings. Amphora was not monophyletic and the two groups recovered corresponded to the subgenera Amphora and Halamphora. Fresh water and marine monoraphids did not form a monophyletic group, although individual genera were monophyletic. Mayamaea was consistently recovered as the sister taxon to a Pinnularia/Caloneis clade. Craticula and Stauroneis were also consistently recovered as sister taxa, but the addition of Navicula intergra to the base of the Stauroneis clade suggested that a new genus was warranted to accommodate this taxon.
Stauroneis phoenicenteron, the type species of Stauroneis, Stauroneis anceps (two moiphotypes) and S. legumen have Geitler's type IC auxosporulation, which has been demonstrated previously also in S. anceps var. siberica. Type IC auxosporulation is possessed by raphid diatoms with quite different valve, girdle and protoplast structure. This, coupled with the variation that occurs between type IC diatoms in, for example, the structure of the copulation envelope, auxospore shape, and the structure of the caps present at the ends of the auxospores, suggests that type IC auxosporulation is not in itself a reliable indicator of close systematic relationship. However, the particular kind of type IC auxosporulation found in Stauroneis also occurs in Craticula and “Navicula” protracta (but not in Navicula sensu strictó). All available evidence, from cell wall and protoplast characters, is consistent with the idea of a close relationship between these taxa and with the idea that the freshwater Stauroneis species belong together in the same genus. The evidence is not conclusive, however, since many of the shared features may be symplesiomorphies.
The history and characteristics of the genus Craticula are reviewed, to justify its separation from Navicula and from the Naviculaceae. Members of the genus have previously been put in Navicula sect. Orthostichae; they include such species as those formerly known as Navicula cuspidata, N. ambigua, N. perrotettii and N. halophila. The closest relatives of Craticula seem to be Stauroneis sensu stricto and the diatoms allied to “Navicula” protracta.
Diatoms possess a remarkable life cycle in which cell size decreases slowly during vegetative cell division and then increases rapidly via special expanding cells called ‘auxospores’, which are usually formed as a result of biparental sexual reproduction. However, auxospores are sometimes produced by single unpaired cells, i.e. uniparentally. We examined the nature of uniparental auxosporulationinSellaphoraandusedatwo-genedatasettostudyphylogeneticrelationshipsbetweenuniparentalandbiparental Sellaphorademesandspecies;wetestedwhetheruniparentalreproductionhasevolvedonceorrepeatedlyinthegenus.Inatleast two of the uniparental demes auxosporulation occurred through autogamy (i.e. intra-tetrad mating within an undivided cell). Maximum likelihood phylogenies indicated four lineages of uniparental Sellaphora and significance tests of alternative topologies, in which combinations of uniparental Sellaphora were constrained to be monophyletic, coupled with likelihood reconstruction of ancestral character states, led to rejection of the hypothesis that uniparental auxosporulation evolved only once in the genus. Uniparentally reproducing lineages appear to arise not infrequently in diatoms but do not persist. Two small extranuclear bodies, apparently containing DNA and lying outside the chloroplast (one close to each pole of the cell), were revealed by DAPI staining.
In this paper, as a sequel of my survey appeared in 1969 in this Journal, supplements are given to the topics “Pairing,” “Gametogenesis,” “Haploid Parthenogenesis,” “Hybrids,” “Automixis,” and “Some Cytological Details” in pennate diatoms. The various kinds of peculiarities are facts—their interpretation in terms of physiology and biochemistry, indeed, rest completely open for future research.
Fistulifera sp. strain JPCC DA0580, a marine pennate diatom, contains extremely high levels of intracellular triglyceride and has been suggested as a promising source of feedstock for biodiesel fuels. JPCC DA0580 was isolated from a mangrove swamp located in Sumiyo Bay below the mouths of the Sumiyo and Yakugachi Rivers in Amami-Ohshima, Kagoshima, Japan. In this study, the morphology and the 18S rDNA sequence of JPCC DA0580 were compared with those of other Fistulifera strains. JPCC DA0580 possesses morphological characters of the genus Fistulifera, namely lightly silicified frustules, a distinct median costa (raphe sternum), and a wart-like central pore (fistula). Morphometric analysis revealed that JPCC DA0580 differs from other Fistulifera species by the presence of a valve with coarser striation and coarser areolation. On the basis of 18S rDNA phylogeny, JPCC DA0580 formed a well-supported clade with other members of the Fistulifera species complex, although the number of nucleotide substitutions was highest in JPCC DA0580. Our results led us to propose the taxonomic name Fistulifera solaris sp. nov. for JPCC DA0580.
Sexual reproduction and protoplast structure are used to check the classification of the naviculoid genus Placoneis Mereschkowsky (Bacillariophyta). The gametangia are closely associated within a robust mucilage capsule throughout auxosporulation, and pairing is ±random with respect to asymmetries of the frustule and protoplast. Two gametes are produced per gametangium, which are morphologically identical but differentiated into active and passive ( physiological anisogamy). The supernumerary nuclei from meiosis II begin to degenerate soon after telophase II, but can still be detected in the initial cells. The gametes become rearranged within the gametangia after meiosis II and plasmogamy takes place via a single, simple aperture. The auxospores expand parallel to the apical axes of the gametangia. The classification of Placoneis in the Cymbellales, as the sister group to the cymbelloid and gomphonemoid diatoms, is supported by valve and protoplast structure, the method of chloroplast division, and by sexual reproduction and auxospore
development. Placoneis seems to occupy an intermediate position in the Cymbellales between the cymbelloid-gomphonemoid cluster and more ancient lineages that include Anomoeoneis Pfitzer, Dickieia Berkeley ex Kiitzing, Rhoicosphenia Grunow and Campylopyxis Medlin. No features can be found that are common to Placoneis and Navicula Bory (from which Placoneis was separated) except for the bilateral symmetry of the valve and the central raphe system, which would be synapomorphies only at a much higher taxonomic level
The allogamous raphid diatom Achnanthes longipes C. A. Agardh possesses a complex breeding system involving interactions between three types of clone : monoecious, unisexual and bisexual. Previous studies showed that these three types can be crossed with each other, with a tendency for sexual characteristics to be inherited : inbred monoecious lineages gave rise to monoecious or, very rarely, to bisexual clones, while inbred unisexual lineages yielded unisexual and bisexual clones. The current paper reports on the progeny of crosses
between monoecious and unisexual clones and their inbred offspring. All three types of clone appeared in the F" and F#, although unisexual clones of opposite sex to the parental clone were not found. Inbreeding depression was observed and also a tendency for `normal' auxosporulation (producing two auxospores per pair of gametangia) to be replaced by ` reduced ' or ` intermediate ' auxosporulation (producing one auxospore per pair). In addition, patterns of incompatibility were observed that were not seen during earlier studies of clones isolated directly from nature. These included the inability of some F" clones to mate with each other, in spite of compatibility with all other clones examined (unisexual, bisexual and monoecious).
Sexual reproduction and auxospore development are described in detail for the first time in Stauroneis. Paired gametangia secrete a wide mucilage envelope and lie apart from each other within this at plasmogamy. Two gametes are produced per gametangium; the superfluous haploid nuclei begin to degenerate soon after meiosis II. The zygotes, initially spherical, develop into rhombic auxospores with prominent organic caps at their poles. During expansion, the auxospores become orientated parallel to the apical axes of the gametangia, whatever their initial orientation. The data support earlier suggestions, made following observations of frustule and protoplast structure, that freshwater Stauroneis species are closely related to Craticula and to "Navicula" protracta
Functional RNA elements do not encode proteins, but rather function directly as RNAs. Many different types of RNAs play important roles in a wide range of cellular processes, including protein synthesis, gene regulation, protein transport, splicing, and more. Because important sequence and structural features tend to be evolutionarily conserved, one way to learn about functional RNAs is through comparative sequence analysis - by collecting and aligning examples of homologous RNAs and comparing them. Covariance models (CMs) are powerful computational tools for homology search and alignment that score both the conserved sequence and secondary structure of an RNA family. However, due to the high computational complexity of their search and alignment algorithms, searches against large databases and alignment of large RNAs like small subunit ribosomal RNA (SSU rRNA) are prohibitively slow. Large-scale alignment of SSU rRNA is of particular utility for environmental survey studies of microbial diversity which often use the rRNA as a phylogenetic marker of microorganisms. In this work, we improve CM methods by making them faster and more sensitive to remote homology. To accelerate searches, we introduce a query-dependent banding (QDB) technique that makes scoring sequences more efficient by restricting the possible lengths of structural elements based on their probability given the model. We combine QDB with a complementary filtering method that quickly prunes away database subsequences deemed unlikely to receive high CM scores based on sequence conservation alone. To increase search sensitivity, we apply two model parameterization strategies from protein homology search tools to CMs. As judged by our benchmark, these combined approaches yield about a 250-fold speedup and significant increase in search sensitivity compared with previous implementations. To accelerate alignment, we apply a method that uses a fast sequence-based alignment of a target sequence to determine constraints for the more expensive CM sequence- and structure-based alignment. This technique reduces the time required to align one SSU rRNA sequence from about 15 minutes to 1 second with a negligible effect on alignment accuracy. Collectively, these improvements make CMs more powerful and practical tools for RNA homology search and alignment.
Auxospore formation has been studied in three Edinburgh populations of Cymatopleura solea and is in all cases associated with sexual reproduction. Vegetative cells are subtly heteropolar, one pole being the site of mitosis, while the other contains the isthmus between the two plates of the single large plastid; for convenience these poles are termed proximal and distal respectively. During sexual reproduction two (rarely three) cells pair by their distal poles and undergo meiosis. Two gametes are produced in each gametangium and these fuse by their tips with the gametes in the other gametangium. Following plasmogamy, one gamete from each gametangium moves through a narrow copulation canal into the other gametangium, so that initially each elongate auxospore is contained almost completely within one of the gametangial frustules. The auxospore is dikaryotic, and its two nuclei move first to the proximal pole and then to the distal pole, where perizonium formation begins. The growth of the perizonium is unipolar and, as its bands are formed, the nuclei move down the expanding auxospore to the proximal pole. Upon completion of the perizonium the nuclei fuse and move to the centre of the cell. Later the diploid fusion nucleus moves to the distal pole and divides, prior to the formation of the initial epivalve. The initial valves are only slightly waisted and are not undulate. Previous reports of auxospore formation in Cymatopleura are analyzed and comparisons made with other raphid diatoms. In the Surirellales there are both behaviourally anisogamous forms and truly isogamous ones; perizonium growth is unipolar where known.
Auxospore formation inAchnanthes hungarica shows the same peculiarities as in other species of the subgenusMicroneis. During cell diminution the outline of the valves changes in an otherwise uncommon manner from simple to more complicated, i.e. the polar regions, at first broadly rounded, become subcuneate. The direction of curving of the distal ends of the raphe to the right or the left is fixed in relation to the organisation of the cell.—In comparison withA. lanceolata var.lanceolata, the new var.minor differs very significantly by its size variation. Other characters peculiar to var.lanceolata, e.g. the middle inflation and the change to isopolarity of the otherwise heteropol transapical axis of the primary cells, also occur in var.minor.—The comparison of eight members of the subgenusMicroneis shows much uniformity in life history, except the mode of fastening to the substrate. In connection with the different behaviour of the daughter cells after cell division there is an obvious correlation between the occurrence of a localized holdfast and the formation of colonies.
InAchnanthes lanceolata pairing occurs by chance in regard to the arrangement of the mother cells, inA. minutissima it is accomplished selectively: contact at the sides occupied by the nucleus is favoured very strongly. In contrast toA. exilis, pairing inA. minutissima occurs by detachment of both partner cells from their stalks, whileA. lanceolata has no stalks at all. The isogamous gamete fusion inA. lanceolata should be understood as a modification of the anisogamous behavior inA. minutissima andA. exilis. For the three species the same constant orientation of the primary cell in relation to the substratum and to the mother thecae is characteristic. The first epivalva always is the raphe valve. InA. lanceolata in connection with the property of the primary cell possessing two chromatophores resp. pyrenoids instead of one, the transapical heteropolarity of the rapheless valve, a specific character, changes to isopolarity. It seems that a sort of induction from the pyrenoids towards the formation of the rapheless valve is at work. InA. lanceolata the pseudoraphe shows a structure hitherto unknown.A. lanceolata “fo.ventricosa
Hust.” is to be eliminated. Var.rostrata (Östrup)Hust. is a good taxon; two new differential characters are found.
Neidium affine is allogamous and exhibits a form of physiological anisogamy in which the behaviour but not the morphology of the two gametes produced by each gametangium differ: one gamete is active, the other passive. The active gamete moves across to the other gametangium via a narrow fusion canal to effect fertilization. Both active gametes move almost simultaneously and appear to facilitate each other's movement. Each ellipsoid zygote (auxospore) produces a partly silicified, bipartite wall, which persists during auxospore expansion, controlling the size and shape of the transverse perizonial bands, and hence the initial cell. A longitudinal perizonium is also produced. The initial epivalve forms after a contraction of the protoplast, and is produced on the opposite side from the longitudinal perizonium. The method of auxospore formation suggests that Neidium is closely related to Amphipleura and Frustulia. The siliceous component of the zygote wall is probably homologous with the scaly coverings of some centric and araphid pennate diatoms.
The morphology and sexual reproduction of the attached diatom Cocconeis scutellum Ehr. var. scutellum have been investigated using field and culture materials. The diatom grew well at 14–22° C and in a medium using enriched full strength seawater or 50% diluted seawater. One gamete was formed without cytokinesis in a gametangium and one auxospore arose from paired gametangia. The size of gametangia and initial cells were 17.8–29.9 μm and 43.3–59.5 μm, respectively. Valve width decreased linearly with decreasing valve length. The regression coefficient between them was invariable with the change of the environment. The transapical striation densities were 7–12 and 7.5–13.5 in 10 μm in araphid and raphid valves, respectively. The density showed a tendency to increase with decreasing valve length in both valves. The densities in both valves, except the small araphid valve, are invariable with the change of the environment. The relationships between valve length and width, and between valve length and striation density have been compared with those of taxa allied to C. scutellum var. scutellum. It is concluded that C. scutellum var. scutellum, as usually delimited, is a heterogenous taxon.
In this paper, as a sequel of my survey appeared in 1969 in this Journal, supplements are given to the topics "Pairing,' "Gametogenesis," "Haploid Parthenogenesis," "Hybrids," "Automixis," and "Some Cytological Details" in pennate diatoms. The various kinds of peculiarities are facts-their interpretation in terms of physiology and biochemistry, indeed, rest completely open for future research. THE EMINENT successes of electron microscopic research make it easy to understand that special and general presentations of biological phenomena in textbooks, exclusively or predominantly, deal with the results of that research. This practice, however, often results in the omission of facts obtained by light microscopy, even if such information contributes to the biological understanding of the object in question, and even if they are not or only accomplished with difficulty by electron microscopy. Examples of that sort
This paper continues a series of studies of the allogamous raphid diatom Achnanthes longipes, which has a complex reproductive system combining unisexual, bisexual and monoecious behaviour. Following earlier work on the effects of inbreeding in the progeny of crosses between two unisexual clones, we studied the progeny of clones that are capable of a high degree of selfing in monoclonal culture (‘monoecious clones’). Three generations of selfed progeny were examined. In addition, we investigated the F1 generation obtained after crossing two different monoecious clones. Monoecious clones produced monoecious or, more rarely, bisexual progeny, but did not give rise to unisexual progeny. As in inbred lineages made by crossing closely related unisexual clones, inbreeding in monoecious lineages leads to a reduction in the number of gametes formed by the gametangia, from two to one. Inbred clones exhibit marked inbreeding depression and only three inbred generations were possible in monoecious lineages. In the third, final inbred generation, monoecious sexual reproduction was initiated in monoclonal cultures but gametes rarely fused and none of the auxospores and initial cells that were formed were viable ; this also occurred when the inbred clones were crossed with any of the other clones available. The significance of inbreeding and other aspects of the breeding system in A. longipes is discussed.
A new monoraphid genus (Pogoneis) is described from a sample of epiphyton growing on the red alga Sarconema filiforme. Its relationship to other achnanthoid species was studied and two of these also proved to require allocation to new genera. Achnanthes hungarica was therefore transferred to Lemnicola nov. gen. and the marine taxon A. taeniata to Pauliella taeniata nov. gen.
Sexual reproduction and auxospore formation of Achnanlhes javanica f. subconstricta have been observed in laboratory culture. This monoraphid diatom showed cis-type behavioural anisogamy and produced two auxospores in one of the paired gametangia. This diatom is unique in that the gametes become re-arranged only in the gametangium producing the stationary gametes, not in that producing the active gametes. Its position is thus obscure in the present classifications of sexual reproduction and auxospore formation. Some modification of these classifications is necessary.