Host (biology)

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Host specificity
)

vectors
for the disease.

In

ectoparasitism
. The host range is the collection of hosts that an organism can use as a partner.

Symbiosis

Symbiosis spans 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] In parasitism, the parasite benefits at the host's expense.[2] In commensalism, the two live together without harming each other,[3] while in mutualism, 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.

brood parasitism of the cuckoo.[6]

Hosts to parasites

predator strategies compared. Their interactions with their hosts form a continuum. Micropredation and parasitoidism are now considered to be evolutionary strategies within parasitism.[2]

Parasites follow a wide variety of evolutionary strategies, placing their hosts in an equally wide range of relationships.[2] Parasitism implies host–parasite coevolution, including the maintenance of gene polymorphisms in 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

  • Definitive or primary host – an organism in which the
    parasite
    reaches 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 L3 larval 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" for

roundworms, where the host has immature juveniles in its muscles and reproductive adults in its digestive tract.[10]

Plant hosts of micropredators

micropredator

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

The range of

polyphagous. One example is the buff ermine moth whose larvae feed on alder, mint, plantain, oak, rhubarb, currant, blackberry, dock, ragwort, nettle and honeysuckle.[18]

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

Plants often produce toxic or unpalatable secondary metabolites to 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. The hawthorn-carrot aphid overwinters on its primary host, a hawthorn tree, and migrates during the summer to its secondary host, a plant in the carrot family.[20]

Host range

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 the epidemiology of the parasitism or disease.

Host range of viruses

For instance, the production of antigenic shifts in Influenza A virus can 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. An influenza vaccine produced against an existing viral strain might 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

Mutualistic hosts

Mycorrhiza, a mutualistic interaction between 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,

gut flora is essential for efficient digestion.[23] Many corals and other marine invertebrates house zooxanthellae, 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 by photosynthesis which 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] Some hermit crabs place pieces of sponge on 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 is

grasses increases the yield of pastures.[29]

Neurotransmitter tyramine produced by commensal Providencia bacteria, which colonize the gut of the nematode Caenorhabditis elegans, bypasses the requirement for its host to biosynthesise tyramine. This product is then probably converted to octopamine by the host enzyme tyramine β-hydroxylase and manipulates a host sensory decision.[30]

Cleaning symbiosis: a Hawaiian cleaner wrasse with its client, a yellowtail wrasse

Hosts in cleaning symbiosis

Hosts of many species are involved in cleaning 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]

a free ride
and which may serve as cleaners

Commensal hosts

molluscs, barnacles and polychaete worms attach themselves to the carapace of the Atlantic 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

The first host to be noticed in ancient times was human:

Giardia lamblia from "his own loose stools".[34]

Hosts to mutualistic symbionts were recognised more recently, when in 1877

See also

References

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  2. ^ .
  3. ^ a b Jackson, John (30 November 2012). "How does the Remora develop its sucker?". National History Museum. Retrieved 19 October 2017.
  4. ^
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  5. ^ Pappas, Stephanie (21 July 2016). "Parasite Evolution: Here's How Some Animals Became Moochers". Live Science. Retrieved 23 October 2017.
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  7. ^ "Parasitoids". Cornell University College of Agriculture and Life Sciences. Retrieved 24 October 2017.
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  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. Archived from the original on 4 July 2015. Retrieved 14 October 2017.
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  12. ^ a b "West Nile Virus Transmission Cycle" (PDF). CDC. Retrieved 19 October 2017.
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  16. ^ "Potato tuberworm: Phthorimaea operculella". Featured Creatures. IFAS. Retrieved 18 October 2017.
  17. . Retrieved 18 October 2017.
  18. ^ Sandhi, Arifin (8 July 2009). "Why Are Phytophagous Insects Typically Specialists?". Science 2.0. Retrieved 18 October 2017.
  19. ^ "Dysaphis crataegi sp. group (Hawthorn - umbellifer aphids)". Genus Dysaphis. InfluentialPoints. Retrieved 18 October 2017.
  20. ^ "The Influenza (Flu) Viruses: Transmission of Influenza Viruses from Animals to People". Centers for Disease Control and Prevention. 2004. Retrieved 18 October 2017.
  21. ^ a b Ecology and Wildlife Biology. Krishna Prakashan Media. pp. 66–67. GGKEY:08L5EQSR3JF.
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  23. ^ "Zooxanthellae... what's that?". National Oceanic and Atmospheric Administration. 6 July 2017. Retrieved 21 October 2017.
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  25. ^ Carefoot, Tom. "Mutualism: Research study 3". Learn about sponges: Symbioses. A Snail's Odyssey. Archived from the original on 13 April 2020. Retrieved 21 October 2017.
  26. ^ Trappe, J. M. (1987). Phylogenetic and ecologic aspects of mycotrophy in the angiosperms from an evolutionary standpoint. CRC Press. {{cite book}}: |work= ignored (help)
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  34. ^ "symbiosis". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)