Fossil Continental Diatoms: Paleolimnology, Evolution, and Biochronology

1995 ◽  
Vol 8 ◽  
pp. 119-138 ◽  
Author(s):  
J. P. Bradbury ◽  
W. N. Krebs
Keyword(s):  
Axial Symmetry ◽  
Brown Algae ◽  
Radial Symmetry ◽  
Centric Diatoms ◽  
Lake Bottom ◽  
Pennate Diatoms

Diatoms are golden brown algae (class Bacillariophyceae) whose cellular contents are enclosed between two valves or shells of silica. They are classified into groups with radial symmetry (centric diatoms) and axial symmetry (pennate diatoms). The latter are subdivided as raphid and araphid diatoms according to the presence or absence of raphes (slit-like structures) that allow diatoms to move along firm surfaces. Many centric and some araphid diatoms are planktonic, maintained by turbulence in the limnetic region of a lake, whereas raphid diatoms live on the lake bottom or are attached to objects in the illuminated zone.

scholarly journals Symmetry Results for Nonvariational Quasi-Linear Elliptic Systems

2010 ◽  
Vol 10 (4) ◽  
Author(s):  
Luigi Montoro ◽  
Berardino Sciunzi ◽  
Marco Squassina
Keyword(s):  
Half Space ◽  
Comparison Principle ◽  
Axial Symmetry ◽  
Elliptic Systems ◽  
Radial Symmetry ◽  
Bounded Domains ◽  
Two Dimensional ◽  
Regular Solutions ◽  
Variational Form ◽  
Weak Comparison Principle

AbstractBy virtue of a weak comparison principle in small domains we prove axial symmetry in convex and symmetric smooth bounded domains as well as radial symmetry in balls for regular solutions of a class of quasi-linear elliptic systems in non-variational form. Moreover, in the two dimensional case, we study the system when set in a half-space.

scholarly journals Recent changes in abundance and cell size of pelagic diatoms in the North American Great Lakes

Phytotaxa ◽  
2013 ◽  
Vol 127 (1) ◽  
pp. 150 ◽  
Author(s):  
EUAN D. REAVIE ◽  
RICHARD P. BARBIERO
Keyword(s):  
Great Lakes ◽  
Cell Size ◽  
Climate Warming ◽  
Lake Huron ◽  
Great Lakes Basin ◽  
The North ◽  
Centric Diatoms ◽  
North American Great Lakes ◽  
Consistent Change ◽  
Pennate Diatoms

Changes in diatom abundance and cell size in Great Lakes phytoplankton collections were examined from two periods, 1996–1999 and 2007–2008. Trends indicate marked shifts in pelagic diatoms, including diatom total biovolume and cell density declines. Concurrent with these changes have been establishments of invasive species, water quality changes and longer stratification periods resulting from climate warming. No consistent change in cell sizes was observed in diatoms between the two periods in the Great Lakes basin as a whole, but lake- and taxon-specific changes were apparent. Cell size declines include centric and pennate diatoms in the spring in Lake Huron and pennate diatoms in the spring in Lake Superior. Increases in cell size occurred for centric diatoms in Lake Erie and pennate diatoms in the summer in lakes Michigan and Ontario. Some of the more dominant taxa exhibited lake-specific shifts. For instance, lightly-silicified diatoms such as Nitzschia increased in length in Lake Huron, possibly as an adaptation to climate warming and/or declining nutrient supplies. Difficulty in explaining the observed changes in cell sizes is acknowledged, but continued study of these trends is critical to understanding impacts on Great Lakes food webs.

scholarly journals Symmetry Transformations in Metazoan Evolution and Development

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 160
Author(s):  
Valeria V. Isaeva ◽  
Nickolay V. Kasyanov
Keyword(s):  
Axial Symmetry ◽  
Hedgehog Signaling ◽  
Phenotypic Expression ◽  
Radial Symmetry ◽  
Metazoan Evolution ◽  
Evolutionary Diversification ◽  
Evolution And Development ◽  
Genetic Mechanisms ◽  
Symmetry Transformations ◽  
Hox Code

In this review, we consider transformations of axial symmetry in metazoan evolution and development, the genetic basis, and phenotypic expressions of different axial body plans. In addition to the main symmetry types in metazoan body plans, such as rotation (radial symmetry), reflection (mirror and glide reflection symmetry), and translation (metamerism), many biological objects show scale (fractal) symmetry as well as some symmetry-type combinations. Some genetic mechanisms of axial pattern establishment, creating a coordinate system of a metazoan body plan, bilaterian segmentation, and left–right symmetry/asymmetry, are analysed. Data on the crucial contribution of coupled functions of the Wnt, BMP, Notch, and Hedgehog signaling pathways (all pathways are designated according to the abbreviated or full names of genes or their protein products; for details, see below) and the axial Hox-code in the formation and maintenance of metazoan body plans are necessary for an understanding of the evolutionary diversification and phenotypic expression of various types of axial symmetry. The lost body plans of some extinct Ediacaran and early Cambrian metazoans are also considered in comparison with axial body plans and posterior growth in living animals.

The catabolic fission of the aromatic ring of phenylalanine by marine planktonic algae

1971 ◽  
Vol 49 (2) ◽  
pp. 259-261 ◽  
Author(s):  
J. R. Vose ◽  
J. Y. Cheng ◽  
N. J. Antia ◽  
G. H. N. Towers
Keyword(s):  
Aromatic Ring ◽  
Marine Species ◽  
Planktonic Algae ◽  
Catabolic Activity ◽  
Centric Diatoms ◽  
Pennate Diatoms

Twenty-two unicellular marine species belonging to seven algal divisions were tested for their ability to cleave the aromatic ring of phenylalanine. Nine species showed production of 14CO2 after incubation with 14C-ring labeled DL-phenylalanine. This catabolic activity was randomly distributed among the algal classes, although it appeared to be particularly common in pennate diatoms and absent in centric diatoms.

Patterns of mucilage production and secretion in pennate diatoms

1989 ◽  
Vol 47 ◽  
pp. 1016-1017
Author(s):  
L. Sicko-Goad ◽  
J. P Kociolek ◽  
E. F. Stoermer
Keyword(s):  
Propylene Oxide ◽  
Growth Forms ◽  
Encapsulated Cells ◽  
Centric Diatoms ◽  
Cacodylate Buffer ◽  
Regular Arrangement ◽  
Pennate Diatoms ◽  
Diamond Knife

Although mucilage production is ubiquitous among diatoms, there have been few studies documenting its production and secretion. Several studies have identified a regular arrangement of Golgi, endoplamic reticulum, and mitochondria as being responsible for mucilage production in centric diatoms. However, such an arrangraent has not been identified for pennate diatoms, although fibrillar vesicles have been described in the vicinity of Golgi and mitochondria and are believed to be involved in mucilage production. The production and secretion of mucilage in certain taxa of pennate diatoms is especially important because it provides various types of growth forms including stalks, tubes and encapsulated cells. The following report compares ultrastructural differences among araphid, monoraphid and biraphid diatoms.Collections of mucilage-producing diatoms exhibiting different growth forms were taken from rocks along the shores of Lakes Michigan and Superior. Samples were field-fixed in 1% paraformaldehyde-glutaraldehyde in cacodylate buffer and stored on ice until samples were returned to the lab. Samples were then postfixed in 1% OsO4, dehydrated in a graded ethanol-propylene oxide series, embedded in Embed 812 and sectioned with a diamond knife. Sections were collected on cleaned formvar- coated 100 mesh copper grids and examined with a Philips 400 TEM.

scholarly journals Variation of Diatoms and Silicon in a Tributary of the Three Gorges Reservoir: Evidence of Interaction

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1369 ◽  
Author(s):  
Wei Xiao ◽  
Yubo Huang ◽  
Wujuan Mi ◽  
Hongyan Wu ◽  
Yonghong Bi
Keyword(s):  
Species Composition ◽  
Cell Density ◽  
Three Gorges Reservoir ◽  
Water Discharge ◽  
Three Gorges ◽  
Diatom Species ◽  
The Three Gorges Reservoir ◽  
The Three Gorges ◽  
Centric Diatoms ◽  
Pennate Diatoms

To gain insight into the variation of diatoms and silicon and their interaction in a tributary of the Three Gorges Reservoir (TGR), the Xiangxi River was chosen as a representative tributary, and dissolved silicon (DSi) and biogenic silicon (BSi) were investigated monthly from February 2015 to December 2016, accompanied by diatom species composition and cell density analyses. The results showed that the diatom population and its relationship with silicon concentration were significantly different between the lacustrine zone and riverine zone (P < 0.05). The cell density in the lacustrine zone (6.20 × 105 ~ 9.97 × 107 cells/L) was significantly higher than that in the riverine zone (7.90 × 104 ~ 1.81 × 107 cells/L) (P < 0.01). Water velocity was a key factor in determining the diatom species composition. Centric diatoms were the dominant species in the lacustrine zone, and pennate diatoms were the primary species in the riverine zone, which indicated that centric diatoms outcompete pennate diatoms under the influence of the TGR’s operation. BSi showed a significant linear relationship with the cell density. DSi had a significant negative relationship with the cell density in the lacustrine zone, while no significant relationship was found in the riverine zone. This meant that the main contributor to BSi was diatoms, but DSi was primarily affected by water discharge, not diatom uptake. It could be deduced that the spatiotemporal heterogeneity of diatom communities was influenced by the TGR’s operation. Silicon cycling in the tributary was significantly affected by diatoms, and the current concentration of DSi was sufficient for diatom growth and showed no significant effects on the diatom community.

Diatomeas planctónicas del litoral de Andalucía (España). Planktonic diatoms from the coast of Andalusia (Spain)

2011 ◽  
Vol 36 ◽  
pp. 5-31
Author(s):  
Mª Carmen Rivera-González ◽  
Pedro M. Sánchez-Castillo
Keyword(s):  
Spatial Distribution ◽  
Annual Cycle ◽  
Skeletonema Costatum ◽  
Pennate Diatom ◽  
Cell Abundance ◽  
Planktonic Diatoms ◽  
Centric Diatoms ◽  
The Mediterranean ◽  
Atlantic Area ◽  
Pennate Diatoms

Español. Se estudian un total de 206 taxones identificados durante el estudio del ciclo anual realizado en las costas de Andalucía a lo largo del año 2000. Destacan, entre las diatomeas céntricas, la subclase Coscinodiscophycidae con 27 taxones y la subclase Chaetocerotophycidae con 28. Entre las pennadas destaca la clase Bacillariophyceae con 76 species. Los géneros que mostraron un mayor número de taxones fueron Chaetoceros, Thalassiosira y Rhizosolenia en el grupo de diatomeas céntricas, mientras que entre las pennadas destacaron los géneros Lyrella, Gyrosigma y Pseudonitzschia. Respecto a su distribución espacial, se han detectado 12 especies exclusivamente atlánticas, mientras que 69 fueron mediterráneas. El resto de taxones presentó una distribución más amplia tanto mediterránea como atlántica. En cuanto a la abundancia celular hemos considerado 119 taxones en la categoría de raros, 57 de habituales y 29 como taxones mayoritarios. Entre los últimos destacaron Hemiaulus sinensis y Eucampia cornuta con carácter marcadamente atlántico, y en la zona mediterránea Cerataulina pelagica y Proboscia alata f. inermes. Las especies más abundantes de todo el litoral andaluz fueron Leptocylindrus minimus, Leptocylindrus danicus, Pseudonitzschia fraudulenta, Skeletonema costatum, Thalassionema nitzschioides, Guinardia striata, Guinardia delicatula y Dactyliosolen phuketensis.English.  In this paper we study 206 taxa found during the annual cycle conducted off the coast of Andalusia during 2000. The most representatives centric diatoms were the subclass Coscinodiscophycidae with 27 taxa and the subclass Chaetocerotophycidae with 28. Among the pennate diatom stand out Bacillariophyceae with 76 species. The Genera that showing the bigger number of taxa were Chaetoceros, Thalassiosira and Rhizosolenia in centric diatoms, whereas in pennate diatoms the Genera Lyrella, Gyrosigma and Pseudonitzschia were dominant. Regarding spatial distribution, 12 species were found exclusively Atlantic, while 69 were Mediterranean. The remaining taxa had a wider distribution both Mediterranean and Atlantic. In terms of cell abundance we considered 119 taxa in the category of rare, 57 taxa in the category of common and 29 as abundant taxa. In the Atlantic area Hemiaulus sinensis and Eucampia cornuta dominated whereas Cerataulina pelagica and Proboscia alata f. inermis characterized the Mediterranean zone. Leptocylindrus minimus, Leptocylindrus danicus, Pseudonitzschia fraudulenta, Skeletonema costatum, Thalassionema nitzschioides, Guinardia striata, Guinardia delicatula, and Dactyliosolen phuketensis were the most representative taxa in the whole Andalusian littoral.

Structure and Composition of Ice Algal Assemblages from the Gulf of St. Lawrence, Magdalen Islands Area

1990 ◽  
Vol 47 (4) ◽  
pp. 780-788 ◽  
Author(s):  
Michèle A. De Sève ◽  
Maxwell J. Dunbar
Keyword(s):  
Dominant Species ◽  
Centric Diatom ◽  
Diatom Species ◽  
Centric Diatoms ◽  
Planktonic Diatom ◽  
Pack Ice ◽  
Landfast Ice ◽  
Algal Assemblages ◽  
Pennate Diatoms ◽  
Index Of Diversity

Two types of ice algal assemblages were found in the Gulf of St. Lawrence: assemblages composed predominantly of pennate diatoms (abundance > 98.0%) and assemblages with a high abundance of centric diatoms (abundance > 46.2%). The first type is similar to Arctic landfast ice algal assemblages with the pennate diatoms Nitzschia cylindrus, N. polaris, and Navicula kariana as dominant species. The second type is similar to drifting ice algal assemblages previously described from the Gulf of St. Lawrence, with a percentage of centric diatom species > 46.2% due to the dominance of the planktonic diatom Thalassiosira nordenskioeldii. Species richness and the Shannon-Weaver index of diversity were low; density ranged from 104–106 × cells∙L−1 and was negatively correlated with percent centric diatoms. Results on the structure and the composition of the ice algal assemblages are related to ice type, i.e. landfast and drifting pack ice, and compared with ice algal assemblages from higher latitudes.

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