词条 | Fragmentation (reproduction) |
释义 |
Fragmentation in multicellular organisms is a form of asexual reproduction in which an organism is split into fragments. Each of these fragments develop into matured, fully grown individuals that are identical to their parents. The splitting may or may not be intentional – it may or may not occur due to man-made or natural damage by the environment or predators. This kind of organism may develop specific organs or zones that may be shed or easily broken off. If the splitting occurs without the prior preparation of the organism, both fragments must be able to regenerate the complete organism for it to function as reproduction. Fragmentation, also known as splitting, as a method of reproduction is seen in many organisms such as filamentous cyanobacteria, molds, lichens, many plants, and animals such as sponges, acoel flatworms, some annelid worms and sea stars. Fragmentation in various organismsMoulds, yeasts and mushrooms, all of which are part of the Fungi kingdom, produce tiny filaments called hyphae. These hyphae obtain food and nutrients from the body of other organisms to grow and fertilize. Then a piece of hyphae breaks off and grows into a new individual and the cycle continues. Many lichens produce specialized structures that can easily break away and disperse. These structures contain both the hyphae of the mycobiont and the algae(phycobiont) (see soredia and isidia). Larger fragments of the thallus may break away when the lichen dries or due to mechanical disturbances(see the section on reproduction in lichens). PlantsFragmentation is a very common type of vegetative reproduction in plants. Many trees, shrubs, nonwoody perennials, and ferns form clonal colonies by producing new rooted shoots by rhizomes or stolons, which increases the diameter of the colony. If a rooted shoot becomes detached from the colony, then fragmentation has occurred. There are several other mechanisms of natural fragmentation in plants.
People use fragmentation to artificially propagate many plants via division, layering, cuttings, grafting, micropropagation and storage organs, such as bulbs, corms, tubers and rhizomes. AnimalsAnimals like sponges and coral colonies naturally fragment and reproduce. Many species of annelids and flat worms reproduce by this method. When the splitting occurs due to specific developmental changes, the terms architomy, paratomy and budding are used. In architomy the animal splits at a particular point and the two fragments regenerate the missing organs and tissues. The splitting is not preceded by the development of the tissues to be lost. Prior to splitting, the animal may develop furrows at the zone of splitting. The headless fragment has to regenerate a complete head. In paratomy, the split occurs perpendicular to the antero-posterior axis and the split is preceded by the "pregeneration" of the anterior structures in the posterior portion. The two organisms have their body axis aligned i.e. they develop in a head to tail fashion. Budding can be considered to be similar to paratomy except that the body axes need not be aligned: the new head may grow toward the side or even point backward (e.g. Convolutriloba retrogemma an acoel flat worm).[4][5] CoralMany types of coral colonies can increase in number by fragmentation that occurs naturally[6] or artificially. Within the reef aquarium hobby, enthusiasts regularly fragment corals for a multitude of purposes including shape control; selling to, trading with, or sharing with others; regrowth experiments; and minimizing damage to natural coral reefs. Both hard and soft corals can be fragmented. Genera that have shown to be highly tolerant of fragmentation include Acropora, Montipora, Pocillopora, Euphyllia, and Caulastraea among many others.[7] Most sea anemones reproduce through fragmentation. There are a variety of methods including longitudinal fission, where the original anemone splits across the middle, forming two equal-sized anemones, and basal laceration, in which small parts of the animal split from the base and form a new anemone.[8] EchinodermsIn echinoderms, the process is usually known as fissiparity (a term also used infrequently for fission in general). Some species can intentionally reproduce in this manner through autotomy. This method is more common during the larval editing stages.[9] Disadvantage of this process of reproductionAs this process is a form of asexual reproduction, it does not produce genetic diversity in the offspring. Therefore, these are more vulnerable to changing environments. See also
References1. ^Rood, S.B., Kalischuk, M.L., and Braatne, J.H. 2003. Branch propagation, not cladoptosis, permits dispersive, clonal reproduction of riparian cottonwoods. Forest Ecology and Management 186: 227–242. 2. ^{{cite web |url=http://www.sbs.auckland.ac.nz/info/schools/nzplants/moss_asexual.htm |title=Archived copy |accessdate=2006-08-06 |deadurl=yes |archiveurl=https://web.archive.org/web/20060927220618/http://www.sbs.auckland.ac.nz/info/schools/nzplants/moss_asexual.htm |archivedate=2006-09-27 |df= }} 3. ^{{cite journal |last1=Equihua |first1=Clementina |title=Diseminación de yemas en Marchantia polymorpha L. (Hepaticae) |journal=Cryptogamie, Bryologie, Lichenologie |date=1987| volume=8| issue=3| page=199-217 |language=Spanish}} 4. ^{{Cite journal| doi = 10.1046/j.1463-6395.2001.00084.x| issn = 1463-6395| volume = 82| issue = 3| pages = 231–239| last = Åkesson| first = Bertil|author2=Robert Gschwentner |author3=Jan Hendelberg |author4=Peter Ladurner |author5=Johann Müller |author6=Reinhard Rieger | title = Fission in Convolutriloba longifissura: asexual reproduction in acoelous turbellarians revisited| journal = Acta Zoologica| accessdate = 2011-07-13| date = 2001-12-01| url = http://homepage.uibk.ac.at/~c719135/pdf/Akesson-Gschwentner-2001.pdf}} 5. ^{{Cite journal| doi = 10.1002/bdrc.20135| issn = 1542-9768| volume = 84| issue = 4| pages = 257–264| last = Egger| first = Bernhard| title = Regeneration: rewarding, but potentially risky| journal = Birth Defects Research. Part C, Embryo Today: Reviews| accessdate = 2011-07-13| date = December 2008| url = http://www.uibk.ac.at/zoology/staff/egger/images/egger-regeneration-review-2008.pdf| deadurl = yes| archiveurl = https://web.archive.org/web/20110811070431/http://www.uibk.ac.at/zoology/staff/egger/images/egger-regeneration-review-2008.pdf| archivedate = 2011-08-11| df = }} 6. ^{{Cite journal| doi = 10.1016/s0022-0981(00)00205-7| issn = 0022-0981| volume = 251| issue = 1| pages = 41–57| last = Lirman| first = Diego| title = Fragmentation in the branching coral Acropora palmata (Lamarck): growth, survivorship, and reproduction of colonies and fragments| journal = Journal of Experimental Marine Biology and Ecology| accessdate = 2011-07-13| date = 2000-08-23| url = http://utweb.ut.edu/hosted/faculty/srice/BIO224.Folder/Invert.Lit.PDF/89.Acropora.fragment.pdf}} 7. ^{{cite web |url=http://www.reefkeeping.com/issues/2002-06/ac/feature/ |title=Coral fragmentation: Not just for beginners |author=Calfo, Anthony |year=2008 |work=Reefkeeping Magazine |publisher=Reef Central |accessdate=2015-05-03}} 8. ^{{cite web |url=https://www.mba.ac.uk/fact-sheet-sea-anemones |title=Fact Sheet: Sea Anemones |work=Marine Biological Association |accessdate=3 September 2018}} 9. ^{{cite book|author1=Helen Nilsson Sköld |author2=Matthias Obst |author3=Mattias Sköld |author4=Bertil Åkesson |editor1=Baruch Rinkevich |editor2=Valeria Matranga |title =Stem Cells in Marine Organisms|chapter =Stem Cells in Asexual Reproduction of Marine Invertebrates|publisher =Springer|year =2009|page=125|isbn = 978-90-481-2766-5|url =https://books.google.com/books?id=-eP2p0VF6VcC&lpg=PA125&dq=Fissiparity&pg=PA125#v=onepage&q=Fissiparity&f=false}} 2 : Fertility medicine|Asexual reproduction |
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