Wikipedia

Host (biology)

Inbiologyandmedicine,ahostis a largerorganismthat harbours a smallerorganism;[1]whether aparasitic,amutualistic,or acommensalistguest(symbiont). The guest is typically provided with nourishment and shelter. Examples includeanimalsplaying host to parasiticworms(e.g.nematodes),cellsharbouringpathogenic(disease-causing)viruses,or abeanplant hosting mutualistic (helpful)nitrogen-fixing bacteria.More specifically inbotany,a host plant suppliesfood resourcesto micropredators, which have anevolutionarily stablerelationship with their hosts similar toectoparasitism.The host range is the collection of hosts that an organism can use as a partner.

Theblack ratis areservoir hostforbubonic plague.Therat fleasthat infest the rats arevectorsfor the disease.

Symbiosis

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Further information:Symbiosis

Symbiosisspans a wide variety of possible relationships between organisms, differing in their permanence and their effects on the two parties. If one of the partners in an association is much larger than the other, it is generally known as the host.[1]Inparasitism,the parasite benefits at the host's expense.[2]Incommensalism,the two live together without harming each other,[3]while inmutualism,both parties benefit.[4]

Most parasites are only parasitic for part of their life cycle. By comparing parasites with their closest free-living relatives, parasitism has been shown to have evolved on at least 233 separate occasions. Some organisms live in close association with a host and only become parasitic when environmental conditions deteriorate.[5]

A parasite may have a long-term relationship with its host, as is the case with all endoparasites. The guest seeks out the host and obtains food or another service from it, but does not usually kill it.[6]In contrast, aparasitoidspends a large part of its life within or on a single host, ultimately causing the host's death, with some of the strategies involved verging onpredation.Generally, the host is kept alive until the parasitoid is fully grown and ready to pass on to its next life stage.[7]A guest's relationship with its host may be intermittent or temporary, perhaps associated with multiple hosts, making the relationship equivalent to theherbivoryof a wild-living animal. Another possibility is that the host–guest relationship may have no permanent physical contact, as in thebrood parasitismof thecuckoo.[6]

Hosts to parasites

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Micropredator,parasite,parasitoid,andpredatorstrategiescompared. Their interactions with their hosts form a continuum. Micropredation and parasitoidism are now considered to beevolutionary strategieswithin parasitism.[2]
See also:Parasitism

Parasites follow a wide variety of evolutionary strategies, placing their hosts in an equally wide range of relationships.[2]Parasitism implieshost–parasite coevolution,including the maintenance ofgene polymorphismsin the host, where there is a trade-off between the advantage of resistance to a parasite and a cost such as disease caused by the gene.[8]

Types of hosts

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  • Definitive or primary host– an organism in which theparasitereaches the adult stage and reproduces sexually, if possible. This is the final host.
  • Secondary or intermediate host– an organism that harbors the sexually immature parasite and is required by the parasite to undergo development and complete its life cycle. It often acts as a vector of the parasite to reach its definitive host. For example,Dirofilaria immitis,the heartworm of dogs, uses the mosquito as its intermediate host until it matures into the infective L3larval stage.

It is not always easy or even possible to identify which host is definitive and which secondary. The life cycles of many parasites are not well understood, and the subjectively or economically more important organism may initially be designated incorrectly as primary. Mislabelling may continue even after the error becomes known. For example trout and salmon are sometimes said to be "primary hosts" forsalmonidwhirling disease,even though themyxosporeanparasite reproduces sexually inside thesludge worm.[9]And where the host harbors the different parasite's phases at different sites within its body, the host is both intermediate and definitive: for exampletrichinosis,a disease caused byroundworms,where the host has immature juveniles in itsmusclesand reproductive adults in its digestive tract.[10]

  • Paratenic or transport host– an organism that harbors the sexually immature parasite but is not necessary for the parasite'sdevelopment cycleto progress. Paratenic hosts serve as "dumps" for non-mature stages of a parasite in which they can accumulate in high numbers. The trematodeAlaria americanais an example: the so-calledmesocercarialstages of this parasite reside intadpoles,which are rarely eaten by the definitive canine host. The tadpoles (or the frogs, following metamorphosis) are more frequently preyed on bysnakes,which then function as paratenic hosts: the mesocercariae do not undergo further development there, but may accumulate, and infect the definitive host once the snake is consumed by a canid.[11]The nematodeSkrjabingylus nasicolais another example, with slugs as the intermediate hosts, shrews and rodents as the paratenic hosts, and mustelids as the definitive hosts.[12]
  • Dead-end,incidental,or accidental host– an organism that generally does not allow transmission to the definitive host, thereby preventing the parasite from completing its development. For example, humans and horses are dead-end hosts forWest Nile virus,whose life cycle is normally betweenculicinemosquitoesand birds.[13]People and horses can become infected, but the level of virus in their blood does not become high enough to pass on the infection to mosquitoes that bite them.[13]
  • Reservoirhost– an organism that harbors apathogenbut suffers no ill effects. However, it serves as a source of infection to other species that are susceptible, with important implications fordiseasecontrol. A reservoir host individual may be reinfected several times.[14]

Plant hosts of micropredators

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Buff erminemothcaterpillar,a polyphagousmicropredator
See also:Larval food plants of Lepidoptera

Micropredation is anevolutionarily stable strategywithin parasitism, in which a small predator lives parasitically on a much larger host plant, eating parts of it.[2]

The range ofplantson which aherbivorousinsect feeds is known as its host range. This can be wide or narrow, but it never includes all plants. A small number of insects aremonophagous,feeding on a single plant. Thesilkwormlarva is one of these, withmulberryleaves being the only food consumed. More often, an insect with a limited host range is oligophagous, being restricted to a few closely related species, usually in the same plant family.[15]Thediamondback mothis an example of this, feeding exclusively onbrassicas,[16]and the larva of thepotato tuber mothfeeds on potatoes, tomatoes and tobacco, all members of the same plant family,Solanaceae.[17]Herbivorous insects with a wide range of hosts in various different plant families are known aspolyphagous.One example is thebuff erminemoth whose larvae feed onalder,mint,plantain,oak,rhubarb,currant,blackberry,dock,ragwort,nettleandhoneysuckle.[18]

Influenzavirus can change by genetic reassortment as it travels between different hosts in its range.

Plants often produce toxic or unpalatablesecondary metabolitesto deter herbivores from feeding on them. Monophagous insects have developed specific adaptations to overcome those in their specialist hosts, giving them an advantage over polyphagous species. However, this puts them at greater risk of extinction if their chosen hosts suffer setbacks. Monophagous species are able to feed on the tender young foliage with high concentrations of damaging chemicals on which polyphagous species cannot feed, having to make do with older leaves. There is a trade off between offspring quality and quantity; the specialist maximises the chances of its young thriving by paying great attention to the choice of host, while the generalist produces larger numbers of eggs in sub-optimal conditions.[19]

Some insect micropredators migrate regularly from one host to another. Thehawthorn-carrot aphidoverwinters on its primary host, ahawthorntree, and migrates during the summer to its secondary host, a plant in thecarrot family.[20]

Host range

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The host range is the set of hosts that a parasite can use as a partner. In the case of human parasites, the host range influences theepidemiologyof the parasitism or disease.

Host range of viruses

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For instance, the production ofantigenic shiftsinInfluenza A viruscan result from pigs being infected with the virus from several different hosts (such as human and bird). This co-infection provides an opportunity for mixing of the viral genes between existing strains, thereby producing a new viral strain. Aninfluenza vaccineproduced against an existingviral strainmight not be effective against this new strain, which then requires a new influenza vaccine to be prepared for the protection of the human population.[21]

Non-parasitic associations

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Mutualistic hosts

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Further information:Mutualism (biology)
Mycorrhiza,amutualistic interactionbetween a plant's roots and a fungus

Some hosts participate in fully mutualistic interactions with both organisms being completely dependent on the other. For example,termitesare hosts to theprotozoathat live in their gut and which digestcellulose,[22]and the humangut florais essential for efficientdigestion.[23]Many corals and other marine invertebrates housezooxanthellae,single-celled algae, in their tissues. The host provides a protected environment in a well-lit position for the algae, while benefiting itself from the nutrients produced byphotosynthesiswhich supplement its diet.[24]Lamellibrachia luymesi,a deep sea giant tubeworm, has an obligate mutualistic association with internal, sulfide-oxidizing, bacterial symbionts. The tubeworm extracts the chemicals that the bacteria need from the sediment, and the bacteria supply the tubeworm, which has no mouth, with nutrients.[25]Somehermit crabsplace pieces ofspongeon the shell in which they are living. These grow over and eventually dissolve away the mollusc shell; the crab may not ever need to replace its abode again and is well-camouflaged by the overgrowth of sponge.[26]

An important hosting relationship ismycorrhiza,a symbiotic association between a fungus and the roots of a vascular host plant. The fungus receives carbohydrates, the products of photosynthesis, while the plant receives phosphates and nitrogenous compounds acquired by the fungus from the soil. Over 95% of plant families have been shown to have mycorrhizal associations.[27]Another such relationship is betweenleguminous plantsand certain nitrogen-fixing bacteria calledrhizobiathat form nodules on the roots of the plant. The host supplies the bacteria with the energy needed for nitrogen fixation and the bacteria provide much of the nitrogen needed by the host. Such crops asbeans,peas,chickpeasandalfalfaare able to fix nitrogen in this way,[28]and mixingcloverwithgrassesincreases the yield of pastures.[29]

Neurotransmittertyramineproduced by commensalProvidenciabacteria, which colonize the gut of the nematodeCaenorhabditis elegans,bypasses the requirement for its host to biosynthesise tyramine. This product is then probably converted tooctopamineby the host enzyme tyramine β-hydroxylase and manipulates a host sensory decision.[30]

Cleaning symbiosis:aHawaiian cleaner wrassewith its client, ayellowtail wrasse

Hosts in cleaning symbiosis

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Further information:Cleaning symbiosisandCleaner fish

Hosts of many species are involved incleaning symbiosis,both in the sea and on land, making use of smaller animals to clean them of parasites. Cleaners include fish, shrimps and birds; hosts or clients include a much wider range of fish, marine reptiles including turtles and iguanas, octopus, whales, and terrestrial mammals.[4]The host appears to benefit from the interaction, but biologists have disputed whether this is a truly mutualistic relationship or something closer to parasitism by the cleaner.[31][32]

Nurse sharkplaying host tocommensalremoras,which gaina free rideand which may serve as cleaners

Commensal hosts

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Further information:CommensalismandPhoresis (biology)

Remoras(also called suckerfish) can swim freely but have evolved suckers that enable them to adhere to smooth surfaces, gaining a free ride (phoresis), and they spend most of their lives clinging to a host animal such as a whale, turtle or shark.[3]However, the relationship may be mutualistic, as remoras, though not generally considered to becleaner fish,often consume parasiticcopepods:for example, these are found in the stomach contents of 70% of thecommon remora.[33]Manymolluscs,barnaclesandpolychaete wormsattach themselves to the carapace of theAtlantic horseshoe crab;for some this is a convenient arrangement, but for others it is an obligate form of commensalism and they live nowhere else.[22]

History

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Further information:Parasitism

The first host to be noticed in ancient times was human:human parasitessuch ashookwormare recorded fromancient Egyptfrom 3000 BC onwards, while inancient Greece,theHippocratic Corpusdescribes humanbladder worm.[34]ThemedievalPersian physicianAvicennarecorded human and animal parasites including roundworms, threadworms, the Guinea worm and tapeworms.[34]InEarly Moderntimes,Francesco Redirecorded animal parasites, while the microscopistAntonie van Leeuwenhoekobserved and illustrated the protozoanGiardia lambliafrom "his own loose stools".[34]

Hosts to mutualistic symbionts were recognised more recently, when in 1877Albert Bernhard Frankdescribed the mutualistic relationship between afungusand analgainlichens.[35]

See also

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References

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  1. ^abCampbell, Neil A.; Reece, Jane B. (2002).Biology(6th ed.). Pearson Education. pp. 540–541.ISBN978-0-201-75054-6.
  2. ^abcdPoulin, Robert;Randhawa, Haseeb S. (February 2015)."Evolution of parasitism along convergent lines: from ecology to genomics".Parasitology.142(Suppl 1): S6–S15.doi:10.1017/S0031182013001674.PMC4413784.PMID24229807.
  3. ^abJackson, John (30 November 2012)."How does the Remora develop its sucker?".National History Museum.Retrieved19 October2017.
  4. ^abGrutter, Alexandra S. (2002)."Cleaning symbioses from the parasites' perspective"(PDF).Parasitology.124(7): S65–S81.doi:10.1017/S0031182002001488.PMID12396217.S2CID26816332.Archived fromthe original(PDF)on 2019-03-07.
  5. ^Pappas, Stephanie (21 July 2016)."Parasite Evolution: Here's How Some Animals Became Moochers".Live Science.Retrieved23 October2017.
  6. ^abDawes, Ben (1976).Advances in Parasitology: Volume 14.Academic Press. pp. 4–6.ISBN978-0-08-058060-9.
  7. ^"Parasitoids".Cornell University College of Agriculture and Life Sciences.Retrieved24 October2017.
  8. ^Woolhouse, M. E. J.; Webster, J. P.; Domingo, E.; Charlesworth, B.; Levin, B. R. (December 2002)."Biological and biomedical implications of the coevolution of pathogens and their hosts"(PDF).Nature Genetics.32(4): 569–77.doi:10.1038/ng1202-569.hdl:1842/689.PMID12457190.S2CID33145462.
  9. ^"Myxosporean parasite, salmonid whirling disease".United States Geological Survey and NOAA Great Lakes Aquatic Nonindigenous Species Information System. 25 September 2012.
  10. ^"CDC - DPDx - Trichinellosis - index".www.cdc.gov.Archivedfrom the original on 4 July 2015.Retrieved14 October2017.
  11. ^Foundations of Parasitology,6th Ed. (Schmidt & Roberts, 2000)ISBN0-07-234898-4
  12. ^Weber, J. -M.; Mermod, C. (1985). "Quantitative aspects of the life cycle ofSkrjabingylus nasicola,a parasitic nematode of the frontal sinuses of mustelids ".Zeitschrift für Parasitenkunde.71(5): 631–638.doi:10.1007/BF00925596.S2CID36435009.
  13. ^ab"West Nile Virus Transmission Cycle"(PDF).CDC.Retrieved19 October2017.
  14. ^Aguirre, A. Alonso; Ostfeld, Richard; Daszak, Peter (2012).New Directions in Conservation Medicine: Applied Cases of Ecological Health.Oxford University Press. p. 196.ISBN9780199731473.
  15. ^Fenemore, P.G. (2016).Plant Pests and Their Control.Elsevier. pp. 125–126.ISBN978-1-4831-8286-5.
  16. ^Talekar, N.S.; Shelton, A.M. (1993)."Biology, ecology and management of the diamondback moth"(PDF).Annual Review of Entomology.38:275–301.doi:10.1146/annurev.en.38.010193.001423.S2CID85772304.Archived fromthe original(PDF)on 2020-06-26.
  17. ^"Potato tuberworm:Phthorimaea operculella".Featured Creatures.IFAS.Retrieved18 October2017.
  18. ^Robinson, Gaden S.; Ackery, Phillip R.; Kitching, Ian; Beccaloni, George W.; Hernández, Luis M. (2023)."Entry forSpilarctia luteum".Database of the World's Lepidopteran Hostplants.Natural History Museum.doi:10.5519/havt50xw.Retrieved18 October2017.
  19. ^Sandhi, Arifin (8 July 2009)."Why Are Phytophagous Insects Typically Specialists?".Science 2.0.Retrieved18 October2017.
  20. ^"Dysaphis crataegisp. group (Hawthorn - umbellifer aphids) ".Genus Dysaphis.InfluentialPoints.Retrieved18 October2017.
  21. ^"The Influenza (Flu) Viruses: Transmission of Influenza Viruses from Animals to People".Centers for Disease Control and Prevention. 2004.Retrieved18 October2017.
  22. ^abEcology and Wildlife Biology.Krishna Prakashan Media. pp. 66–67. GGKEY:08L5EQSR3JF.
  23. ^Sears CL (October 2005). "A dynamic partnership: celebrating our gut flora".Anaerobe.11(5): 247–51.doi:10.1016/j.anaerobe.2005.05.001.PMID16701579.
  24. ^"Zooxanthellae... what's that?".National Oceanic and Atmospheric Administration. 6 July 2017. Archived fromthe originalon 13 April 2020.Retrieved21 October2017.
  25. ^Cordes, E.E.; Arthur, M.A.; Shea, K.; Arvidson, R.S.; Fisher, C.R. (2005)."Modeling the mutualistic interactions between tubeworms and microbial consortia".PLOS Biology.3(3): 1–10.doi:10.1371/journal.pbio.0030077.PMC1044833.PMID15736979.
  26. ^Carefoot, Tom."Mutualism: Research study 3".Learn about sponges: Symbioses.A Snail's Odyssey. Archived fromthe originalon 13 April 2020.Retrieved21 October2017.
  27. ^Trappe, J. M. (1987).Phylogenetic and ecologic aspects of mycotrophy in the angiosperms from an evolutionary standpoint.CRC Press.{{cite book}}:|work=ignored (help)
  28. ^Laranjo, Marta; Alexandre, Ana; Oliveira Solange (2014)."Legume growth-promoting rhizobia: An overview on theMesorhizobiumgenus? ".Microbiological Research.160(1): 2–17.doi:10.1016/j.micres.2013.09.012.PMID24157054.
  29. ^Tow, P.G.; Lazenby, Alec (2000).Competition and Succession in Pastures.CABI. p. 75.ISBN978-0-85199-703-2.
  30. ^O’Donnell, Michael P.; Fox, Bennett W.; Chao, Pin-Hao; Schroeder, Frank C.; Sengupta, Piali (17 June 2020)."A neurotransmitter produced by gut bacteria modulates host sensory behaviour".Nature.583(7816): 415–420.Bibcode:2020Natur.583..415O.doi:10.1038/s41586-020-2395-5.PMC7853625.PMID32555456.
  31. ^Losey, G.S. (1972). "The Ecological Importance of Cleaning Symbiosis".Copeia.1972(4): 820–833.doi:10.2307/1442741.JSTOR1442741.
  32. ^Poulin. R; Grutter, A.S. (1996)."Cleaning symbiosis: proximate and adaptive explanations".BioScience.46(7): 512–517.doi:10.2307/1312929.JSTOR1312929.
  33. ^Cressey, R.; Lachner, E. (1970). "The parasitic copepod diet and life history of diskfishes (Echeneidae)".Copeia.1970(2): 310–318.doi:10.2307/1441652.JSTOR1441652.
  34. ^abcCox, Francis E. G. (June 2004)."History of human parasitic diseases".Infectious Disease Clinics of North America.18(2): 173–174.doi:10.1016/j.idc.2004.01.001.PMID15145374.
  35. ^"symbiosis".Oxford English Dictionary(Online ed.).Oxford University Press.(Subscription orparticipating institution membershiprequired.)
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