Article

Inbreeding influence on sexual reproduction of Achnanthes longipes Ag. (Bacillariophyta)

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  • Tomalgae BV (Belgium)
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Abstract

While crossing inbred clones of Achnanthes longipes Ag., obtained in laboratory culture, various kinds of sexual processes took place that were not characteristic of clones isolated from natural populations. “Normal” and “reduced” reproductive types, intermediates between these, paedogamous gamete fusion and haploid parthenogenesis were found in mixed cultures of clones from the first inbred generation. Furthermore, polyploid and triradiate auxospores were observed when clones of the second inbred generation were crossed.

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... Within species, a recent genome doubling distinguishes natural populations of the polar centric species, Ditylum brightwellii (Koester et al., 2010), and WGDs apparently occur in strains maintained in long-term cell culture as well . Finally, and perhaps most compellingly, simultaneous fusions of three or four gametes, leading to the formation of autopolyploid auxospores (i.e., zygotes), have been directly observed in several raphid pennate diatoms, including Cocconeis (Geitler, 1927), Craticula (Mann and Stickle, 1991), Dickea (Mann, 1994), Achnanthes (Chepurnov and Roschin, 1995), and Seminavis (Chepurnov et al., 2002). The latter set of observations, in particular, led to the prediction that polyploidy might be an important driver of speciation in diatoms (Mann, 1994(Mann, , 1999a. ...
... Finally, although our analyses highlighted allopolyploidy as a potentially important mode of WGD in diatoms, it is important to note that autopolyploidy may be shown to be equally, if not more, common with increased sampling. Indeed, autopolyploid formation has been directly observed in vitro for several different species of raphid pennate diatoms (Geitler, 1927;Mann and Stickle, 1991;Mann, 1994;Chepurnov and Roschin, 1995;Chepurnov et al., 2002). ...
... Although the rate of meiotic nonreduction in diatoms is unknown, Mann (1994) observed that failed cleavage in gametangia of the raphid pennate diatom, Dickea ulvacea, led to the formation of 'double gametes' that produced a dikaryotic, triploid-like zygote following fusion with a reduced gamete (Mann, 1994). Second, although polyspermy is thought to occur relatively rarely in plants (Ramsey and Schemske, 1998), the production of triploid and tetraploid zygotes from simultaneous gamete fusions has been observed in culture studies of several raphid pennate diatoms (Geitler, 1927;Mann and Stickle, 1991;Mann, 1994;Chepurnov and Roschin, 1995;Chepurnov et al., 2002), suggesting that this may be a principal pathway to polyploidization in diatoms. These studies have found mixed populations of cooccurring haploid, triploid, and tetraploid zygotes following one or two rounds of crossing in culture, . ...
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Premise of the study Diatoms are one of the most species-rich lineages of microbial eukaryotes. Similarities in clade age, species richness, and contributions to primary production motivate comparisons to flowering plants, whose genomes have been inordinately shaped by whole genome duplication (WGD). These events that have been linked to speciation and increased rates of lineage diversification, identifying WGDs as a principal driver of angiosperm evolution. We synthesized a relatively large but scattered body of evidence that, taken together, suggests that polyploidy may be common in diatoms. Methods We used data from gene counts, gene trees, and patterns of synonymous divergence to carry out the first large-scale phylogenomic analysis of genome-scale duplication histories for a phylogenetically diverse set of 37 diatom taxa. Key results Several methods identified WGD events of varying age across diatoms, though determining the exact number and placement of events and, more broadly, inferences of WGD at all, were greatly impacted by gene-tree uncertainty. Gene-tree reconciliations supported allopolyploidy as the predominant mode of polyploid formation, with particularly strong evidence for ancient allopolyploid events in the thalassiosiroid and pennate diatom clades. Conclusions Whole genome duplication appears to have been an important driver of genome evolution in diatoms. Denser taxon sampling will better pinpoint the timing of WGDs and likely reveal many more of them. We outline potential challenges in reconstructing paleopolyploid events in diatoms that, together with these results, offer a framework for understanding the evolutionary roles of genome duplication in a group that likely harbors substantial genomic diversity.
... Within species, a recent genome doubling distinguishes natural populations of the polar centric species, Ditylum brightwellii (Koester et al., 2010), and WGDs apparently can occur in strains maintained in long-term cell culture as well . Finally, and perhaps most compellingly, simultaneous fusions of three or four gametes, leading to the formation of autopolyploid auxospores (i.e., zygotes), have been directly observed in several raphid pennate diatoms, including Cocconeis (Geitler, 1927), Craticula (Mann and Stickle, 1991), Dickea (Mann, 1994), Achnanthes (Chepurnov and Roschin, 1995), and Seminavis (Chepurnov et al., 2002). The latter set of observations, in particular, led to the prediction that polyploidy might be an important driver of speciation in diatoms (Mann, 1994(Mann, , 1999b. ...
... Finally, with respect to hybridization and polyploidy, raphid pennate diatoms have received far more attention than any other group of diatoms (see introduction and Mechanisms of polyploid formation in diatoms section below). There is direct evidence for autopolyploid formation within raphid pennates in vitro (Mann, 1994;Chepurnov and Roschin, 1995) and strong genetic evidence for natural hybrids in the few species that have been examined (Casteleyn et al., 2009;Tanaka et al., 2015). Their unique suite of traits, species richness, availability of established and emerging genetic models, and extensive body of research on their reproductive biology establish raphid pennates as the premier lineage for uncovering the mechanisms and evolutionary consequences of polyploidy in diatoms. ...
... Finally, although our analyses highlighted allopolyploidy as a potentially important mode of WGD in diatoms, it is important to note that autopolyploidy may be shown to be equally, if not more, common with increased sampling. Autopolyploid formation has been directly observed in vitro for several different species of raphid pennate diatoms (Geitler, 1927;Mann and Stickle, 1991;Mann, 1994;Chepurnov and Roschin, 1995;Chepurnov et al., 2002). ...
Article
Full-text available
Premise of the Study Diatoms are one of the most species‐rich lineages of microbial eukaryotes. Similarities in clade age, species richness, and primary productivity motivate comparisons to angiosperms, whose genomes have been inordinately shaped by whole‐genome duplication (WGD). WGDs have been linked to speciation, increased rates of lineage diversification, and identified as a principal driver of angiosperm evolution. We synthesized a large but scattered body of evidence that suggests polyploidy may be common in diatoms as well. Methods We used gene counts, gene trees, and distributions of synonymous divergence to carry out a phylogenomic analysis of WGD across a diverse set of 37 diatom species. Key Results Several methods identified WGDs of varying age across diatoms. Determining the occurrence, exact number, and placement of events was greatly impacted by uncertainty in gene trees. WGDs inferred from synonymous divergence of paralogs varied depending on how redundancy in transcriptomes was assessed, gene families were assembled, and synonymous distances (Ks) were calculated. Our results highlighted a need for systematic evaluation of key methodological aspects of Ks‐based approaches to WGD inference. Gene tree reconciliations supported allopolyploidy as the predominant mode of polyploid formation, with strong evidence for ancient allopolyploid events in the thalassiosiroid and pennate diatom clades. Conclusions Our results suggest that WGD has played a major role in the evolution of diatom genomes. We outline challenges in reconstructing paleopolyploid events in diatoms that, together with these results, offer a framework for understanding the impact of genome duplication in a group that likely harbors substantial genomic diversity.
... Among most diatom species, this leads to mean cell size diminution in the population (MacDonald, 1869;Pfitzer, 1869), and the maximum size of cells in a population is restored by auxosporulation followed by initial cell development. Normally, cell size restoration is achieved as a result of sexual reproduction, but vegetative enlargement has also been observed in some cases (Geitler, 1935;Round et al., 1990;Mann, 1993Mann, , 2011Chepurnov and Roshchin, 1995;Kaczmarska et al., 2013). ...
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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.
... One striking event which happened during the crossing experiments was the occurrence of a possible triploid auxospore, a rare phenomenon in diatoms but already noted in a few pennate species (Mann, 1994;Chepurnov et al., 2002Chepurnov et al., , 2005Poulíčková et al., 2007). The triploid auxospore presented an unusual triradiate shape, a feature rarely observed (Chepurnov & Roschin, 1995). Auxospore caps were only present on the two lower branches (Fig. 15). ...
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Haslea provincialis Gastineau, Hansen & Mouget, sp. nov., is a new, morphologically semicryptic blue diatom discovered on the French shores of the Mediterranean Sea. Like H. ostrearia and H. karadagensis, H. provincialis shares the capacity to synthesize a marennine-like blue pigment. Sexual reproduction between clones of H. provincialis has been repeatedly observed and resulted in viable initial cells. There were no sexual interactions with sexually competent clones of H. ostrearia or H. karadagensis, as would be expected for a separate biological species. There are strong similarities between the H. provincialis pigment and the marennine produced by H. ostrearia, evidenced by UV-visible spectrophotometry and Raman spectrometry. However, unlike the marennine from H. ostrearia, no differences were found between the extracellular and the intracellular forms of the pigment in H. provincialis. This indicates that the synthesis pathways and excretion mechanisms among the three ‘blue’ Haslea may be species-specific. Molecular taxonomy and phylogeny (based on rbcL, cox1 and SSU V4 DNA sequences) confirmed the distinct position of this species among the blue Haslea species. Haslea provincialis occurs in environments from which H. ostrearia has already been reported (mostly based on the presence of the blue cell vacuoles). Possible species misidentifications and the impact of the complex geological history of the Mediterranean Sea on blue diatom diversification are also discussed.
... Our observations of triploid and tetraploid auxospores in A. copulata extend a growing list of species in which autopolyploid formation has been demonstrated (e.g. Geitler 1932;Mann & Stickle 1991;Mann 1994b;Chepurnov & Roshchin 1995;Chepurnov et al. 2005;Poulíčková et al. 2007), providing evidence of the kind of mechanism that could generate polyploid series. However, the chromosome counts for A. ovalis and A. copulata are almost the same, despite a considerable difference in cell size (compare Figs 2 and 16, these representing approximately the same stage of the life cycle, slightly outside the sexual size range). ...
Article
Cytological characteristics of the mitotic cycle, sexual reproduction and auxospore formation are described for three members of the type group of Amphora A ovalis, A copulata and minutissima All have a single lobed ventral chloroplast, nuclei with granular heterochromatin and a single nucleolus (unusually large in A ovalis) Amphora copulata is heterothallic, with two mating types that do not differ in gamete behaviour All three species reproduce allogamously via fusion of two rearranged gametes per gametangium to produce elongate zygotes enclosed within the volume delimited by the gametangial thecae Pairing is strictly via the ventral sides of the cells, with tight apposition of the cells, and expansion of the auxospores is strictly perpendicular to the gametangium long axes Comparisons are made with other Amphora species, particularly A proteus (also belonging to the subgenus Amphora) and A arcus Meiosis is described in detail in A copulata, revealing no movement of the nucleus away from the dorsal position it occupies during the mitotic cycle, a synizetic knot in early prophase, no cytokinetic accompanying meiosis 11, and rapid degeneration of the supernumetary nuclei in the gametic cells, the usual two acytokinetic mitoses accompany formation of the initial epivalve (which lacks a functional raphe) and hypovalve The potential for formation of autopolyploids is demonstrated in A copulata Nevertheless, chromosome counts of 2n = 34 in A copulata, 2n = 28 or 30 in A ovalis and an undetermined but not significantly lower number in A minutissima, suggest that homoploid evolution is more likely than polyploid In mixed sexualized populations of the species, no interbreeding occurs, supporting separation of minutissima from copulata Measurements of initial cell sizes, coupled with slight differences in valve width and pattern, suggest that A copulata may be a species complex
... Auxosporulation and sexual reproduction have been observed in Achnanthes brevipes var. intermedia (Ku¨tzing) Cleve, Achnanthes longipes Agardh, Achnanthes subconstricta (Meister) Toyoda and Achnanthes subssesilis Ku¨tzing (Karsten, 1899;Idei & Chihara, 1991;Mizuno, 1994;Chepurnov & Roschin, 1995;Chepurnov & Mann, 1999;Sabbe et al., 2004). These reports primarily describe sexual reproductive behaviour, rather Correspondence to: Kensuke Toyoda. ...
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This study clarifies the fine structure of the vegetative and initial valves of Achnanthes yaquinensis and briefly compares them to other Achnanthes species. It also elucidates the structure of the perizonium, based on auxospore development in short-term cultures. The araphid valve has marginal ridges and terminal spines that allow connecting valves to form a chain. The terminal spines develop from the rapheless sternum. The complete cingulum consists of 3–5 split bands with two rows of areolae. These features can be used to discriminate species within the genus. Sexual reproduction is isogamous with two mother cells producing two auxospores, which are enclosed in mucilage. The perizonium develops on one side of an auxospore only, comprising one large central longitudinal band and four closed bands. There are no transverse perizonial bands. The raphid valve of the initial cell forms first, underneath the longitudinal perizonium, followed by the araphid valve, which is not covered by any perizonial bands. The araphid valve of the initial cells lacks a marginal spine, and the rapheless sternum lies more centrally than in the vegetative cell. The relationship of the genus Achnanthes to other monoraphid diatoms is discussed briefly.
... Meister) Toyoda and Achnanthes subssesilis Kütz. (see Karsten 1899;Idei & Chihara 1991;Mizuno 1994;Chepurnov & Roschin 1995;Chepurnov & Mann 1999;Sabbe et al. 2004). These reports primarily describe the sexual reproductive behavior of the marine and brackish water species, but omit observations on the fine structure of perizonium. ...
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The present study clarifies the fine structure of the vegetative frustules, initial valves and perizonium of Achnanthes crenulata Grunow. The valves of the vegetative cell are distinctly linear-lanceolate with an undulate margin. The valve face is quite flat and in girdle view is smoothly curved as in species of Gephyria (Bacillariophyceae). However, the valve face of the initial cells is slightly rounded and does not have an undulate margin. Furthermore, the rapheless sternum is centrally positioned along the apical axis of the araphid initial valve. As this taxon develops from auxospore to initial valve, it forms only longitudinal perizonial bands; no transverse bands arise. The perizonium consists of three silicified bands: one large, central longitudinal plate and two bands that underlie this plate; these two bands are either open or closed. This taxon has several conspicuous structures compared to other marine species of Achnanthes, but the structure of the perizonium supports the position of A. crenulata within Achnanthes sensu stricto.
... anglica (Kü tzing) Peragallo (Mann 1982b) and Nitzschia recta Hantzsch (Mann 1986), although Achnanthes species have a well-developed system of longitudinal perizonial bands. Williams (2001) proposed that the plethora of peculiar shapes that emerge in the immediate post auxospore valves in F. virescens, and presumably in Diatoma moniliformis Kü tzing (Potapova & Snoeijs 1997), were because of the absence of transverse perizonial bands; this could also be why irregularly shaped and triradiate auxospores (reported by Hendey 1951; Schmid in PickettHeaps et al. 1990; Chepurnov & Roshchin 1995) are common in Achnanthes spp. (Sabbe et al. 2004). ...
Article
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Examination of Grammatophora marina from rough and clonal cultures showed that cell size changes were more flexible than is generally reported for diatoms. Allogamous sexual auxosporulation took place through copulation between small male cells and larger female cells, but only in mixed rough culture and never in clonal cultures. Auxospores were also formed without copulation in clonal cultures ('uniparental auxosporulation') and these, like sexual auxospores, developed through formation of a perizonium, which consisted of a series of transverse bands. All of these bands, including the primary band, were open. Circular scales were present in the auxospore wall before initiation of perizonium formation and irregular, elongate structures lined the suture of the transverse perizonium. Perizonium and scales resembled those of another araphid pennate diatom, Gephyria media. Initial cells were formed within the perizonium and consisted of an initial epivalve with a simplified structure, an initial hypovalve (formed beneath the perizonium suture) and a third, normally structured valve formed beneath the epivalve; the epivalve was then sloughed off. Initial cells of similar configuration but often aberrant morphology could also be formed through expansion from vegetative cells, without involvement of a perizonium. Vegetative cells were also capable of limited enlargement through simple expansion without formation of an initial cell, and abrupt size reduction. Cell size ranges in populations from different regions suggest that G. marina may contain pseudocryptic species.
... Additionally, initial advances in the fields of inbreeding and outbreeding in pennate diatoms have been realized in the laboratory of A. M. Roschin (e.g. Roschin 1990, Chepurnov and Roschin 1995), suggesting that regulatory and/or incompatibility mechanisms exist in some taxa to prevent monoecy and inbreeding. ...
Article
Center for Great Lakes and Aquatic Sciences, University of Michigan, 2200 Bonisteel Boulevard, Ann Arbor, Michigan 48109–2099
... Several processes could cause polyploidization and aneuploidization in culture. Polyploid auxospores resulting from fusion of more than two gametes has been observed in several pennate diatoms (Chepurnov and Roschin 1995, Chepurnov et al. 2002, 2005, and polyspermy was suggested to occur in the centric diatom T. punctigera . Treatments with Ca 2+ or Mg 2+ deficiency or colchicine inhibit cytokinesis and result in multinucleate cells in Cyclotella cryptica (Badour 1968, Oey andSchnepf 1970). ...
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The enormous species diversity of diatoms correlates with the remarkable range of cell sizes in this group. Nuclear DNA content relates fundamentally to cell volume in other eukaryotic cells. The relationship of cell volume to G1 DNA content was determined among selected members of the genus Thalassiosira, one of the most species-rich and well-studied centric diatom genera. Both minimum and maximum species-specific cell volume correlated positively with G1 DNA content. Phylogeny based on 5.8 S and ITS rDNA sequences indicated that multiple changes in G1 DNA content and cell volume occurred in Thalassiosira evolution, leading to a 1,000-fold range in both parameters in the group. Within the Thalassiosira weissflogii (Grunow) G. A. Fryxell et Grunow species complex, G1 DNA content varied 3-fold: differences related to geographic origin and time since isolation; doubling and tripling of G1 DNA content occurred since isolation in certain T. weissflogii isolates; and subcultures of T. weissflogii CCMP 1336 diverged in DNA content by 50% within 7 years of separation. Actin, beta-tubulin, and Spo11/TopVIA genes were selected for quantitative PCR estimation of haploid genome size in subclones of selected T. weissflogii isolates because they occur only once in the T. pseudonana Hasle et Heimdal genome. Comparison of haploid genome size estimates with G1 DNA content suggested that the most recent T. weissflogii isolate was diploid, whereas other T. weissflogii isolates appeared to be polyploid and/or aneuploid. Aberrant meiotic and mitotic cell divisions were observed, which might relate to polyploidization. The structural flexibility of diatom genomes has important implications for their evolutionary diversification and stability during laboratory maintenance.
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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)
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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).
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Diatoms are one of the most species-rich groups of eukaryotic microbes known. Diatoms are also the only group of eukaryotic micro-algae with a diplontic life history, suggesting that the ancestral diatom switched to a life history dominated by a duplicated genome. A key mechanism of speciation among diatoms could be a propensity for additional stable genome duplications. Across eukaryotic taxa, genome size is directly correlated to cell size and inversely correlated to physiological rates. Differences in relative genome size, cell size, and acclimated growth rates were analyzed in isolates of the diatom Ditylum brightwellii. Ditylum brightwellii consists of two main populations with identical 18s rDNA sequences; one population is distributed globally at temperate latitudes and the second appears to be localized to the Pacific Northwest coast of the USA. These two populations co-occur within the Puget Sound estuary of WA, USA, although their peak abundances differ depending on local conditions. All isolates from the more regionally-localized population (population 2) possessed 1.94 +/- 0.74 times the amount of DNA, grew more slowly, and were generally larger than isolates from the more globally distributed population (population 1). The ITS1 sequences, cell sizes, and genome sizes of isolates from New Zealand were the same as population 1 isolates from Puget Sound, but their growth rates were within the range of the slower-growing population 2 isolates. Importantly, the observed genome size difference between isolates from the two populations was stable regardless of time in culture or the changes in cell size that accompany the diatom life history. The observed two-fold difference in genome size between the D. brightwellii populations suggests that whole genome duplication occurred within cells of population 1 ultimately giving rise to population 2 cells. The apparent regional localization of population 2 is consistent with a recent divergence between the populations, which are likely cryptic species. Genome size variation is known to occur in other diatom genera; we hypothesize that genome duplication may be an active and important mechanism of genetic and physiological diversification and speciation in diatoms.
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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.
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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.
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The genus Dickieia is re-established for Navicula ulvacea, N. subinflata and N. expecta. Dickieia cells contain one complex chloroplast per cell; this consists of two ‘K’-shaped halves, linked by an isthmus containing the single discoid pyrenoid. The pyrenoid lies near one side of the girdle at the centre, while the nucleus lies opposite. Neither the nucleus nor the chloroplast move significantly within the cell during the cell cycle. The valves contain round poroids with hymenate occlusions. The raphe-sternum lacks accessory ribs and the central internal raphe endings are simple and straight. The epitheca contains several narrow, porous girdle bands. Auxosporulation is unusually variable in D. ulvacea and can be allogamous (with isogamy) or automictic, though the gametangia are always paired. Plasmogamy is brought about principally through expansion of the gametes until they meet and fuse. The orientation of the auxospores bears no fixed relation to the gametangia. Haploid parthenogenesis and the formation of polyploid auxospores and ‘double’ gametes are reported and their significance discussed. Dickieia belongs within the Cymbellales and is closely related to the Rhoicospheniaceae and Anomoeoneidaceae.
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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