Dinoflagellates

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Dinoflagellates
Ceratium sp.

Ceratium sp.

Systematics
Classification : Creature
Domain : Eukaryotes (eukaryota)
without rank: Diaphoreticks
without rank: Sar
without rank: Alveolata
without rank: Dinoflagellates
Scientific name
Dinoflagellata
( Bütschli , 1885) Cavalier-Smith , 1991

The dinoflagellates ( Dinoflagellata ; from Gr. Δῖνος dinos "whirling" and Latin flagellum "whip, flagellum"), also known as Peridineae and armored flagellants , are a taxon that predominantly includes unicellular organisms . Their distinguishing features include two flagella present during the mobile life cycle and chromosomes that are condensed during interphase . Dinoflagellates do not have histones . Worldwide, a distinction is made between around 2,400 recent species (as of 2012), most of which live in the sea and form a major part of phytoplankton . The sub-strain includes both autotrophic and heterotrophic species.

features

Basic characteristics

Basal blueprint of a dinoflagellate

There is an extremely large variety of shapes within the dinoflagellates. The size ranges from 2 µm ( Gymnodinium simplex ) to 2 mm ( Noctiluca miliaris ), with most species between 10 and 100 µm in size.

The shape of the free-swimming cell is egg-shaped to rounded, with the anterior being usually more pointed than the posterior . Most dinoflagellates have two long flagella . A scourge is directed backwards (longitudinal scourge), it lies in the inner section in a groove of the cell body, but mostly protrudes more or less long to the rear. The other flagella, which strikes in a plane perpendicular to it (transverse flagella), winds to the left around the cell body, it is usually completely within a furrow. The transverse flagella allows the cell to rotate and contributes most to propulsion. The longitudinal flagellum serves primarily to control the direction of movement. This arrangement of the flagella is called dinokont. In the case of the prorocentrales, in contrast to this, both flagella sit freely at the rear end of the cell, this is called desmokont. In some genera there are completely different, sometimes flagellate cells.

In many species, the vacuoles lying directly below the cell membrane are filled with cellulose and thus reinforced to form more or less massive plates. If such intracellular plates are present, this envelope is called theka and the corresponding species thekat. If the alveoli are not or only very slightly reinforced, the species are called athekat or naked. The theka forms a mosaic of individual panels; this can be used to identify the species.

A transverse furrow, the so-called belt (cingulum), runs around the cell, dividing it into an anterior (episoma) and posterior (hyposoma). If there is a theka, the parts are called epitheka or hypotheka. If there is no theca, one speaks of athecatic dinoflagellates. In morphological descriptions of these dinoflagellates, the terms epicone and hypocone are used instead of epi- and hypotheka. A longitudinal furrow, the so-called sulcus, runs posteriorly from the transverse furrow. The transverse flagella strikes in the cingulum, the longitudinal flagellum in the sulcus.

Scourges

The longitudinal flagellum is usually somewhat flattened. It occasionally has a sparse trimmings of cilia ( mastigonema ), which can also be completely absent. The transverse flagellum is connected longitudinally to the cell within the furrow-like cingulum via a ribbon-like connection. It beats with a wave-like movement. Their free outer edge is usually covered with hairs. The cingulum usually does not surround the cell in a circular manner, but is somewhat spiral, so that the rear end of the transverse flagella lies further back than the root, the spiral is usually relatively flat, but can be quite steep in some genera. When striking, the cell is set in a rotating movement (always to the left).

Amphiesma and cell skeleton

The outer region of the cell body of the dinoflagellates has a number of morphological peculiarities. Below the cell membrane sits a system of flat vacuoles , termed amphiesmale vesicles or alveoli, these have the dinoflagellates with a number of other single-celled organisms such as ciliates together (ciliates) with which they, according to this feature, in the taxon Alveolata are combined . The outer region that contains the vacuoles is called the amphiesma or cortex (cortex). Inside the vesicles of the armored (thecate) dinoflagellates, a cellulose plate is deposited in each vesicle, which can ultimately combine to form a closed shell. Due to the formation and position within a vacuole, however, the envelope lies within the cell (intracellularly) and is therefore enclosed by the cell membrane. In the case of a few dinoflagellates, the vacuoles of the amphiesma are filled exclusively with liquid. For many others, they contain solid material that does not stiffen to form a closed armor; these are collectively called athekat (i.e. without theka). In the thecate dinoflagellates, the arrangement of the plates is used to determine the genera and species, each plate has been given a special name in a sophisticated system. In some species there is a second, thin layer of fibers called the pellicle below the vesicle. In addition to cellulose, it contains the polymer sporopollenin . In the case of many dinoflagellates, the outer shell can be thrown off (called ecdysis), and the pellicle then forms the outer shell of cysts called persistence stages.

Some basal athecate dinoflagellates, for example of the genus Oxyrrhis , have small, often star-shaped flakes made of cellulose on the surface ( i.e. extracellular). Others, such as Dicroerisma and Actinscus, have internal skeletal elements made of silicon dioxide . In the case of Achradina and Monaster , these can enclose the cell like a basket.

Cell nucleus

Within the eukaryotes, the nucleus of the dinoflagellates has unique properties, which is why it is given the special term dinokaryon. Their DNA is not organized in nucleosomes and their characteristic proteins, the histones, are almost completely absent. Overall, the protein content of the cell nucleus is far lower than that of other eukaryotes, usually only around 10 percent. Instead of the histones, only special proteins occurring in them are detected, the origin of which could be detected by horizontal gene transfer from viruses (dinoflagellate viral nucleoproteins; DVNPs). While it was earlier believed that histones are completely absent, have now all Histonfamilien if detected in lower grade and in some quite divergent structure in the dinoflagellates, they probably have with them a special role in the transcription maintained.

The DNA content of the dinoflagellates is among the highest in all eukaryotes, and their genome is unusually extensive. The chromosomes are also condensed during the interphase and are visible in the electron microscope. The chromosomes form a garland structure, with the individual fibrils only 2.5 nm in diameter. The remaining eukaryotes have fibrils ten times the diameter with a central nucleohiston strand. The structure of the chromosomes was compared to liquid crystals . The non-coding DNA content of the dinoflagellates is extraordinarily high. It is believed that only the outer, loop-shaped ends of the chromosomes that protrude outward from the nucleus contain coding segments. The mitosis is extremely unusual for them. The membrane surrounding the nucleus is preserved throughout the mitotic cycle. During the division, finger-shaped indentations form, which ultimately penetrate the core completely and thus produce torus- like structures. The mitotic spindle is formed within the torus, with its attachment sites (the kinetochores ) located in the inner membrane of the torus. Depending on the kin, between one and five (or six) such tunnels are formed through the cell nucleus. During the interphases, too, the cell nucleus, in addition to the usual nuclear envelope, is traversed by a network of membranes from which the tunnel structures are formed.

Furthermore, the modified base hydroxymethyluracil (HOMeU) is only detected in the DNA within the dinoflagellates. With a total proportion of 4–19%, it replaces 12–70% of the thymine bases . The number of chromosomes varies between 5 in Syndinium turbo and 274 in Ceratium hirundinella .

Bioluminescence

Dinoflagellate bioluminescence caused by breaking the waves

Some species are capable of bioluminescence , this glow being a response to mechanical stimulation. In nature, these are deformations of the cell membrane that are caused by shear forces . Heavily churned water such as breaking waves or fast swimming fish can trigger such stimulations. A reaction can also be induced in the laboratory using chemicals. The dinoflagellates are the only bioluminescent autotrophic organisms such as representatives of the genera Gonyaulax , Protogonyaulax , Pyrodinium and Pyrocystis . Bioluminescence can also be observed in heterotrophic species such as Noctiluca miliaris or some members of the genera Ceratium .

The emitted light is blue-green and has a maximum at 474-476 nm. Since this wavelength is close to the maximum transmittance of seawater, it is assumed that the visibility of the light causes the selective advantage. In experiments with luminous and non-luminous species it could be shown that predation was reduced in the case of bioluminescence . Presumably, enemies will be deterred by the flash of light. As with almost all types of bioluminescence, this is due to a reaction between luciferases and luciferins .

Toxins

Some species produce extremely potent poisons. The saxitoxin example is from members of the genus Alexandrium ( Gonyaulax produced). If the poisonous dinoflagellates are eaten by mussels, the poison accumulates in the mussels and can then also be dangerous for humans. With a mass reproduction of poisonous species, so much poison is produced that fish and other marine life are also killed. Karenia brevis produces brevetoxins and can lead to mass deaths of fish, birds and mammals in the “ red tides ” they generate .

The Ciguatera disease , a type of fish poisoning, is caused by metabolic products of the Gambierdiscus toxicus species . The dinoflagellate toxins ciguatoxin and maitotoxin find their way into fish via the food chain , which are also highly toxic. The poisoning can be fatal in humans.

The toxin from Pfiesteria piscicida, on the other hand, is not accumulated through the food chain, but is directly toxic to fish and humans.

Distribution and habitats

Noctiluca scintillans is a marine creature

Dinoflagellates are cosmopolitan in salt water as well as in fresh water and can colonize many habitats there due to their variety of shapes. Around 75% of all species are assigned to the marine plankton, with the greatest biodiversity in tropical waters. But they are also benthic creatures and also penetrate the sediments. They can also be found in the polar region or in sea ice.

Fewer species are common in freshwater. 420 species from inland waters are known worldwide (around 17 percent of the number of species) that inhabit lakes, ponds and moors. The distribution area extends roughly from the equator to 78 ° north latitude ( Spitzbergen (island) ). The height differences range from −209 meters in Israel to 4150 meters in the high mountain lakes of Mexico.

Since some species enter into symbioses or live as parasites, living things are also used as habitats. For example, dinoflagellates live as endosymbionts in many corals and are then referred to as zooxanthellae . Autotrophic species are dependent on light-flooded layers of water, heterotrophic species can also penetrate into completely dark depths.

nutrition

About half of the dinoflagellates are autotrophic and can use inorganic carbon with the help of the assimilation of the chloroplasts. However, almost all photosynthetically active species are auxotrophic and require vitamins ( cobalamine , biotin , thiamine ) for catalytic purposes. These are absorbed via phagocytosis . Autotrophic species also enter into a symbiosis with cnidarians (Cnidaria), in particular corals, molluscs (Mollusca) but also foraminifera (Foraminifera) and ciliate (Ciliata).

Heterotrophic dinoflagellates feed on a diverse spectrum of plankton organisms, ranging from nanoplankton to large diatoms . This also includes dinoflagellates of their own and other species, detritus and even eggs and larvae of copepods . In the simplest case, the food is ingested by phagocytosis (for example Noctiluca miliaris ). Thanks to special cell structures such as peduncles or pallium , heterotrophic dinoflagellates can also feed on organisms that are many times larger than themselves ( e.g. Pfiesteria or Protoperidinium ).

Autotrophy

The autotrophic species contain plastids with chlorophyll a and some species also contain chlorophyll c. As the main carotenoid , they usually contain peridinin instead of fucoxanthin . Their color ranges from yellow-brown to reddish, as the chlorophyll is covered by brown and yellow carotenoids and red xanthophylls . Starch is the main product of assimilation stored in granules outside of the chloroplasts. However, fatty substances were also detected. The plastid wall usually consists of three membranes that are not connected to the endoplasmic reticulum .

Basically, dinoflagellates can accommodate very different plastids that differ from the basic type. This is due to phagotrophy , which is also maintained in autotrophic species. This led to another, tertiary endocytobiosis in the tribal history . The ingested organisms can come from different groups, such as Haptophyta , Cryptophyceae , Heterokontophyta or a chlorophyte . The chloroplast, which originally came from the red algae , is completely or largely regressed and in the latter case appears as an inactive eye spot (stigma). Occasionally there is also a nucleomorph in the chloroplasts .

Basic types of heterotrophy

Basic types of heterotrophy in dinoflagellates

The feeding mechanisms of heterotrophic dinoflagellates can be described by three basic types.

  • Phagocytosis : The prey is directly and completely absorbed through the sulcus and enclosed in a feeding vacuole (for example Noctiluca miliaris ).
  • Myzocytosis : A characteristic strand of plasma is everted from the sulcus. This peduncle pierces the cell envelope of the prey and sucks the cell contents into a feeding vacuole. The cell components of the prey are not digested immediately. Chloroplasts, for example, can be retained and thus continue to function as kleptoplastids in dinoflagellates (for example dinophysis ). The cell envelope of the prey is not enclosed in the vacuole.
  • Pallium : From the sulcus, a tubular or sail-shaped pseudopodium is everted out that surrounds the prey with a thin layer of cell plasma and thus forms a feeding vacuole. Since this vacuole is formed outside the theca, the size of the pallium and thus the size of the prey is not limited by the size of the dinoflagellate, so that a much larger prey can be digested ( e.g. protoperidinium .) The prey is located in the pallium digested, and ingested in liquefied form.

The basic types of myzocytosis and pallium occur mainly in thecate (armored) species and are sometimes referred to as extracellular digestion. On closer inspection this is not true, because in any case the prey is digested in a feeding vacuole within the cell plasma, but these feeding vacuoles can be located outside the theca. This can be interpreted as overcoming the restrictions imposed by the theca and opened up a wider range of prey for the heterotrophic species.

Catching prey

The atypical dinoflagellate Noctiluca miliaris has a short tentacle that is used like a liming rod. Food particles such as diatoms and detritus stick to it and are then carried by the tentacle to the cytostome.

The thecate dinoflagellate Stoeckeria algicida, on the other hand, uses a suddenly ejected protein filament (English: tow filament ) to capture the prey over a comparatively large distance. A comparable filament is used by Protoperidinium to anchor itself to diatoms chains.

Reproduction

The reproduction takes place mainly vegetatively. In armored species, the plates are usually blown up at an angle to the belt, with the missing half growing back later. But there is also the possibility that the armor is thrown off and the daughter cells completely regenerate it. Under unfavorable living conditions, thick-walled, persistent cysts develop.

Sexual reproduction has only been demonstrated in a few species. Here anisogamy with zygotic nuclear phase change as well as isogametes , which arise in gametangia, are released and merge with one another, were described.

Life cycle of the dinoflagellates 1- binary fissiparia , 2- sexual reproduction , 3-planozygotes, 4-hypnozygotes, 5-planomeiocytes.

Ecological importance

Together with the diatoms , the dinoflagellates are the main primary producers of organic matter in the sea, so together with the diatoms they form the main part of the base of the food pyramid . In high mountain lakes they can make up up to 50% of the biomass.

With their specialized feeding mechanisms, the heterotrophic dinoflagellates can eat a wide range of prey organisms, ranging from nanoplankton smaller than 10 µm to large chain-forming diatoms. Thereby providing the heterotrophic dinoflagellates an important part of the microbial loop represents (English: microbial loop .)

Under favorable conditions for them, certain species multiply to an extreme extent in tropical and subtropical waters, so that the upper layers of the sea turn red to brown. This algal bloom is also known as the red tide or red tide.

Biostratigraphy

Due to their very resistant, organic cell wall, dinoflagellate cysts are not destroyed by calcium dissolution, but remain intact even after long periods of time. In addition, many cysts have a characteristic shape. This plays a decisive role in the age dating ( biostratigraphy ) of sediments .

Other fossil groups such as foraminifera have too little biodiversity and dinoflagellate cysts occur in almost all waters where they are used today as climate indicators . It was not until 1988 that Germany began to set up "Dinoflagellate zones", which are now being regularly improved.

Systematics

Due to the sometimes very complex life cycles of the dinoflagellates, the systematic structure is the subject of scientific discussion. The taxon is considered polyphyletic . The structure given here (generic examples) essentially follows Adl et al. 2012:

  • Dinophyceae
  • Dinophysiphycidae (Dinophysaceae Stein 1883 [Citharistaceae Kofoid & Skogsberg 1928 ; Ornithocercaceae Kofoid & Skogsberg 1928 ])
  • Noctilucaceae Kent, 1881
  • Noctiluca 1836
  • Noctiluca scintillans (Macartney) Kofoid & Swezy, 1921 ( syn.Noctiluca miliaris Suriray , nomen invalidum)

supporting documents

Unless specified under individual evidence, the article is based on the following documents:

literature

  • Stefan Nehring: Permanent Dinoflagellate Cysts in German Coastal Waters: Occurrence, Distribution and Significance as Recruitment Potential (= Christian-Albrechts-Universität zu Kiel . Institute for Oceanography: Reports from the Institute for Oceanography , No. 259). Institute for Oceanography , Department of Marine Planktology, Kiel 1994, DNB 943792797 (Dissertation University of Kiel [1994], 231 pages).

Web links

Commons : Dinoflagellates  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c Fernando Gómez (2012): A quantitative review of the lifestyle, habitat and trophic diversity of dinoflagellates (Dinoflagellata, Alveolata). Systematics and Biodiversity 10 (3): 267-275. doi: 10.1080 / 14772000.2012.721021
  2. ^ Loeblich, Alfred R. & Loeblich, Laurel A. (1985). Dinoflagellates: Structure of the amphiesma and re-analysis of thecal plate patterns . Hydrobiologia, vol. 123, no. 2: 177-179. ( Abstract and full text ).
  3. ↑ Georgi K. Marinov & Michael Lynch (2016): Diversity and Divergence of Dinoflagellate Histone Proteins. G3 Genes Genomes Genetics 6: 397-422. doi: 10.1534 / g3.115.023275 .
  4. ↑ Gregory S. Gavelis, Maria Herranz, Kevin C. Wakeman, Christina Ripken, Satoshi Mitarai, Gillian H. Gile, Patrick J. Keeling, Brian S. Leander (2019): Dinoflagellate nucleus contains an extensive endomembrane network, the nuclear net. Scientific Reports 9, Article number: 839. doi: 10.1038 / s41598-018-37065-w
  5. ↑ Taylor: The Biology of Dinoflagellates . Blackwell, 1987, ISBN 0-632-00915-2 , p. 160.
  6. ↑ Taylor: The Biology of Dinoflagellates . Blackwell, 1987, ISBN 0-632-00915-2 , p. 618.
  7. ↑ Landsberg JH (2002). The effects of harmful algal blooms on aquatic organisms . Reviews in Fisheries Science, 10 (2): 113-390.
  8. ↑ Swift A., Swift T. (1993). Ciguatera . In: J Toxicol Clin Toxicol . 31: 1-29. ( Abstract ).
  9. ^ Moeller PD, Beauchesne KR, Huncik KM, Davis WC, Christopher SJ, Riggs-Gelasco P., Gelasco AK (2007). Metal complexes and free radical toxins produced by Pfiesteria piscicida . Environ. Sci. Technol. 41 (4): 1166-72. doi : 10.1021 / es0617993
  10. ↑ a b c Schnepf, Eberhard and Elbrächter, Malte (1992). Nutritional strategies in dinoflagellates . Europ. J. Phycology, vol. 28: 3 - 24.
  11. ^ A b Per J. Hansen and António J. Calado (1999): Phagotrophic mechanisms and prey selection in free-living dinoflagellates . Journal of Eukaryotic Microbiology, vol. 46, no. 4: 382 - 389. doi: 10.1111 / j.1550-7408.1999.tb04617.x .
  12. ↑ Gordon, A. and Dyer, B. (2005). Relative contribution of exotoxin and micropredation to icthyotoxicity of two strains of Pfiesteria shumwayae (Dinophyceae) Harmful algae , vol. 4, no.2: 423-431.
  13. ↑ Kiyotaka Takishitaa, Kazuhiko Koikeb, Tadashi Maruyamaa and Takehiko Ogatab (2002). Molecular Evidence for Plastid Robbery (Kleptoplastidy) in Dinophysis, a Dinoflagellate causing Diarrhetic Shellfish Poisoning . Protist, Vol. 153, 293-302. PMID 12389818 .
  14. ^ Gaines, G. & Taylor, FJR (1984). Extracellular digestion in marine dinoflagellates . Journal of Plankton Research, Vol. 6, No. 6: 1057-1061.
  15. ↑ Hae Jin Jeong, Jae Seong Kim, Jong Hyeok Kim, Seong Taek Kim, Kyeong Ah Seong, Tae Hoon Kim, Jae Yoon Song, Soo Kyeum Kim (2005). Feeding and grazing impact of the newly described heterotrophic dinoflagellate Stoeckeria algicida on the harmful alga Heterosigma akashiwo . Mar Ecol Prog Ser, Vol. 295: 69-78.
  16. ↑ Naustvoll, Lars J. (2001). The role of heterotrophic dinoflagellates in marine pelagic food webs . Dissertation, University of Oslo.
  17. ↑ Azam, SD; Fennel, T .; Field, JG; Gray, JS; Meyer-Reil, LA; Thingstad, F. (1983). The ecological role of water column microbes in the sea . Marine Ecology Progress Series, vol. 10: 257 - 263. ( full text ; PDF; 3.8 MB).
  18. ↑ Adl, SM, Simpson, AGB, Lane, CE, Lukeš, J., Bass, D., Bowser, SS, Brown, MW, Burki, F., Dunthorn, M., Hampl, V., Heiss, A. , Hoppenrath, M., Lara, E., le Gall, L., Lynn, DH, McManus, H., Mitchell, EAD, Mozley-Stanridge, SE, Parfrey, LW, Pawlowski, J., Rueckert, S., Shadwick, L., Schoch, CL, Smirnov, A. and Spiegel, FW (2012): The Revised Classification of Eukaryotes. Journal of Eukaryotic Microbiology , 59: pp. 429-514, 2012, PDF Online .