Riftia pachyptila
| Riftia pachyptila | ||||||||||
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Riftia pachyptila |
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| Systematics | ||||||||||
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| Scientific name of the genus | ||||||||||
| Riftia | ||||||||||
| Jones, 1981 | ||||||||||
| Scientific name of the species | ||||||||||
| Riftia pachyptila | ||||||||||
| Jones , 1981 |
Riftia pachyptila is a kind from the family of siboglinidae (Siboglinidae, older name: Pogonophora) and the only species of its genus. The species has received alot of attention both inside and outside of sciencedue to its size, its way of life at hydrothermal vents in the deep sea ( black smokers ), and its symbiotic way of life with chemoautotrophic bacteria. Several hundred scientific publications and some film and television documentaries have appearedon Riftia .
features
Riftia lives inside a tube that is firmly anchored to the sea floor and which the animal never leaves. The body consists of four clearly separated sections. The front end carries a tuft of vivid red filaments, some of which have grown together like lamellas. The filaments are attached to a stiff and firm structure called the obturaculum. In the event of disturbances, the animal pulls the filaments back into the tube, which is tightly closed by the obturaculum as a lid. The obturacular region is followed by a muscular section called the vestimentum. When the filaments are stretched out, the vestiment blocks access to the living tube. This is where the animal's brain sits, its short, muscular heart and an excretory organ. In addition, the genital pores and special glands that secrete the material of the living tube are located on the vestimentum. The vestimentum is followed by a very long trunk region, which consists of a central cavity that is bounded by a muscular tube and an outer skin (epidermis). The epidermis is covered by a smooth cuticle, which mainly consists of fibers of the protein collagen . Inside the central body cavity sits a lobed organ, the trophosome, in which the symbiotic sulfur bacteria live, which form the sole nutritional basis of Riftia . In addition, the gonads (gonads) extend here. The posterior end, known as the opisthosome, consists of numerous short, offset segments and carries rows of long bristles; its function is to anchor the animal in the living tube.
The Riftia living tube is smooth and straight, it is closed at the rear end. It is made of a leather-like material that is flexible in consistency and largely consists of beta- chitin fibers . The tube allows the front end some mobility. The length of the tube can, under optimal conditions, exceed a length of two meters, but in most populations it is considerably shorter, it considerably exceeds the length of the living animal. In the animals that live on the basalt floor of the submarine ridge, it is completely exposed and is only anchored in a crevice at the rear end. In animals that live on sediment, it can also be partially buried.
symbiosis
Riftia lives in symbiosis with a type of bacteria that belongs to the gamma- proteobacteria . The worm cannot ingest food because it has neither a mouth nor an intestine; therefore he is completely dependent on this symbiote for his survival. Riftia was the first species in which the symbiosis with a sulfur bacterium was observed and has remained a model organism for this relationship to this day. Such symbioses are now known to be much more widespread than originally thought. Although much has been found out about the bacterial species, despite decades of attempts, it has not yet been possible to cultivate it. Among other things, large parts of the genome and proteome have been deciphered and the species was given the provisional name Candidatus Endoriftia persephone .
The symbiotic bacteria gain energy through the oxidation of sulfide ions with the oxygen in the seawater. Sulphide is not stable in free water, but is released together with a number of metal ions from hydrothermal springs on the sea floor, which are related to volcanic activity on mid-ocean ridges. Here, seawater seeped into crevices is heated up by magma lying at a shallow depth and enriched with minerals. Other species of beard worms can also use oxygen-free silt or rotting organic matter as sulphide sources; this has never been observed in Riftia . The bacteria oxidize the sulfide to sulfate, releasing energy. You can also use several metabolic pathways to reduce carbon dioxide dissolved in water to organic matter. This makes them not only a source of energy for Riftia , but also a source of carbon and biomass. Riftia supports its endosymbionts by constantly gushing in sulphide-rich water, which does not well out of the crevices on the seabed, but in a small-scale strongly changing composition. It also helps to facilitate the assimilation of carbon dioxide through an adjusted pH value and removes harmful metabolic products such as elemental hydrogen. There is evidence that Riftia may also be able to use this hydrogen for energy. The bacterium may be able to switch to nitrate breathing in low-oxygen conditions, or at least it can absorb nitrate as a nitrogen source from seawater.
For eukaryotes like Riftia, sulfide is actually a cytotoxin. The species has found a special way of enriching this toxic substance and delivering it to its symbiont. To do this, she uses a form of the red blood pigment hemoglobin , which is not enclosed in cells, but is found freely dissolved in the plasma. Riftia has three different forms of hemoglobin, the globin fraction of which is largely the same, but these components are composed differently. The globin has one binding site for oxygen and one for sulfide, spatially separated from each other, the binding site of which contains the sulfur-containing amino acid cysteine as a functional component. Due to the high hemoglobin content, the tentacles of Riftia are colored red.
The symbionts are enclosed in a special organ, the trophosome, and there within specialized cells, the bacteriocytes. Due to their small size, they make up the vast majority of cells, but only about a quarter of the biomass. The cells of the trophosome are not of endodermal origin, as previously assumed, but of mesodermal origin.
In the meantime it has been proven that the growing worm does not bring the bacteria with it from the mother animal, but has to take them up from the environment each time in the course of development. There they can also be found freely living. Several tube worm species can use the same endosymbiont.
Reproduction and development
Riftia is gender segregated, the gender ratio probably 1: 1. The male animals release flagellated spermatozoa into the open water, which swim to the female animals and fertilize the eggs (internally) there. The fertilized eggs are released into the water. They develop into the typical larval stage of the annelids, the trochophora larva. These larvae are also the main stage of spread. Since the hydrothermal springs at which the animals live are quite short-lived (their lifespan is on average hardly longer than that of the worms), they are absolutely dependent on an efficient distribution path. It is observed that newly created springs that are hundreds of kilometers away from existing ones can be settled quickly. From the life of the larvae of around 38 days and the typical flow patterns, an average distribution distance of around 100 kilometers was derived. Despite an intensive search, living larvae have never actually been found directly in the ocean. Once a favorable new habitat has been discovered, the swimming larva changes into a ground-living larva stage. At this stage the symbiotic bacteria are absorbed. The larvae grow into adult worms. In this way, the intestinal canal temporarily formed in the larva becomes functionless and regressed.
The growth of Riftia is exceptionally fast. If the tube length is measured as a measure of growth, it can reach record values of 85 centimeters per year for an invertebrate, but within a tube of 2 meters in length sits a worm that is only around 80 centimeters in size.
ecology
The species has the typical characteristics of a pioneer species in its habitat : rapid colonization, very rapid youth growth. From observations at sources on the sea floor, we know that it is indeed a first-time colonist. Experimentally scraped-free sources were repopulated by the species within a very short time. At longer existing sources, the species is gradually being displaced by other species. The mussel species Bathymodiolus thermophilus is often a subsequent settler. In favorable habitats, riftia can reach very high densities of many hundreds of individuals per square meter, which provide a habitat for a biocenosis of growth species. In general, however, the habitat of Riftia is a typical extreme habitat in which only a few species can live, but which here reach extreme densities.
Adult beard worms hardly have any predators. The crab species Bythograea thermydron and Munidopsis subsquamosa have been observed grazing filaments of living worms.
distribution
Riftia pachyptila lives exclusively in the Pacific. There it inhabits a long section of the East Pacific Ridge , leaving out the sections close to the pole and the Galapagos Ridge that branches off at right angles. Here the species was discovered and described by the marine biologist Meredith Jones during a dive with the deep-sea submersible Alvin . The species was not found in other submarine spreading zones investigated (not a single rift-dwelling beard worm species on the mid-Atlantic ridge to this day!). In the central, coastal section of the ridge off the Bay of California, animals were found at hydrothermal springs in sedimentary rock, the endosymbionts of which apparently differ somewhat from those of the mid-ocean ridges on basalt rock.
supporting documents
- ↑ an overview: Nicole Dubilier, Claudia Bergin, Christian Lott (2008): Symbiotic diversity in marine animals: the art of harnessing chemosynthesis. Natue Review Microbiology 6: 725-740. doi : 10.1038 / nrmicro1992
- ^ Franck Zal, Emmanuelle Leize, François H. Lallier, André Toulmond, Alain Van Dorsselaer, James J. Childress (1998): S-Sulfohemoglobin and disulfide exchange: The mechanisms of sulfide binding by Riftia pachyptila hemoglobins. Proceedings of the National Academy of Sciences 95 (15): 8997-9002.
- ↑ Monika Bright & Angelika Sorgo (2003): Ultrastructural reinvestigation of the trophosome in adults of Riftia pachyptila (Annelida, Siboglinidae). Invertebrate Biology 122 (4): 347-368 doi : 10.1111 / j.1744-7410.2003.tb00099.x
- ^ Tara L. Harmer, Randi D. Rotjan, Andrea D. Nussbaumer, Monika Bright, Andrew W. Ng, Eric G. DeChaine, Colleen M. Cavanaugh (2008): Free-Living Tube Worm Endosymbionts Found at Deep-Sea Vents. Applied and Environmental Microbiology 74 (12): 3895. doi : 10.1128 / AEM.02470-07
- ^ Adam G. Marsh, Lauren S. Mullineaux, Craig M. Young, Donald T. Manahan (2001): Larval dispersal potential of the tubeworm Riftiapachyptila at deep-sea hydrothermal vents. Nature 411, 77-80. doi : 10.1038 / 35075063
- ↑ Julie C. Robidart, Annelys Roque, Pengfei Song, Peter R. Girguis: Linking Hydrothermal Geochemistry to Organizmal Physiology: Physiological Versatility in Riftia pachyptila from Sedimented and Basalt-hosted Vents. PLoS one 6 (7): e21692. doi : 10.1371 / journal.pone.0021692
literature
- Monika Bright & Francois H. Lallier (2010): The biology of Vestimentiferan tubeworms. Oceanography and Marine Biology: An Annual Review 48: 213-266.
- Ana Hilario, Marıa Capa, Thomas G. Dahlgren, Kenneth M. Halanych, Crispin TS Little, Daniel J. Thornhill, Caroline Verna, Adrian G. Glover: New perspectives on the ecology and evolution of siboglinid tubeworms. In: PloS one. Volume 6, number 2, 2011, p. E16309, doi : 10.1371 / journal.pone.0016309 , PMID 21339826 , PMC 3038861 (free full text) (review).
