Symbiosis

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This article is about the biological phenomenon, for other uses see Symbiosis (disambiguation)
Clownfish amid sea anemone tentacles

The term symbiosis (from the Greek: σύν syn "with"; and βίωσις biosis "living") commonly describes close and often long-term interactions between different biological species. The term was first used in 1879 by the German mycologist Heinrich Anton de Bary, who defined it as "the living together of unlike organisms."[1][2] The definition of symbiosis is in, and the term has been applied to a wide range of biological interactions. The symbiotic relationship may be categorized as being mutualistic, parasitic, or commensal in nature.[3][4] Others define it more narrowly, as only those relationships from which both organisms benefit, in which case it would be synonymous with mutualism.[1][5][6]

Symbiotic relationships include those associations in which one organism lives on another (ectosymbiosis, such as mistletoe), or where one partner lives inside the other (endosymbiosis, such as lactobacilli and other bacteria in humans or zooxanthelles in corals). Symbiotic relationships may be either obligate, i.e., necessary for the survival of at least one of the organisms involved, or facultative, where the relationship is beneficial but not essential for survival of the organisms.[7][8]

Contents

[edit] Commensalism

Main article: Commensalism

Commensalism describes a relationship between two living organisms where one benefits and the other is not significantly harmed or helped. It is derived from the English word commensal, meaning "sharing food" and used of human social interaction. The word derives from the medieval Latin word, formed from com- and mensa, meaning "sharing a table".[9][10]

Commensal relationships may involve one organism using another for transportation (phoresy) or for housing (inquilinism), or it may also involve one organism using something another created, after its death (metabiosis). Examples of metabiosis are hermit crabs using gastropod shells to protect their bodies and spiders building their webs on plants.

[edit] Parasitism

Main article: Parasitism

A parasitic relationship is one in which one member of the association benefits while the other is harmed.[11] Parasitic symbioses take many forms, from endoparasites that live within the host's body to ectoparasites that live on its surface. In addition, parasites may be necrotrophic, which is to say they kill their host, or biotrophic, meaning they rely on their host's surviving. Biotrophic parasitism is an extremely successful mode of life. Depending on the definition used, as many as half of all animals have at least one parasitic phase in their life cycles, and it is also frequent in plants and fungi. Moreover, almost all free-living animals are host to one or more parasite taxa. An example of a biotrophic relationship would be a tick feeding on the blood of its host.

[edit] Symbiosis and evolution

Leafhoppers protected by an army of meat ants

While historically, symbiosis has received less attention than other interactions such as predation or competition,[12] it is increasingly recognised as an important selective force behind evolution,[7][13] with many species having a long history of interdependent co-evolution.[14] In fact, the evolution of all eukaryotes (plants, animals, fungi, and protists) is believed under the endosymbiotic theory to have resulted from a symbiosis between various sorts of bacteria.[7][15][16]

[edit] Symbiogenesis

The biologist Lynn Margulis, famous for her work on endosymbiosis, contends that symbiosis is a major driving force behind evolution. She considers Darwin's notion of evolution, driven by competition, as incomplete and claims that evolution is strongly based on co-operation, interaction, and mutual dependence among organisms. According to Margulis and Dorion Sagan, "Life did not take over the globe by combat, but by networking."[17]

[edit] Co-evolution

Symbiosis played a major role in the co-evolution of flowering plants and the animals that pollinate them. Many plants that are pollinated by insects, bats, or birds have highly specialized flowers modified to promote pollination by a specific pollinator that is also correspondingly adapted. The first flowering plants in the fossil record had relatively simple flowers. Adaptive speciation quickly gave rise to many diverse groups of plants, and, at the same time, corresponding speciation occurred in certain insect groups. Some groups of plants developed nectar and large sticky pollen, while insects evolved more specialized morphologies to access and collect these rich food sources. In some taxa of plants and insects the relationship has become dependent,[18] where the plant species can only be pollinated by one species of insect.[19]

[edit] Notes

  1. ^ a b Wilkinson 2001
  2. ^ Douglas 1994, p. 1
  3. ^ Dethlefsen L, McFall-Ngai M, Relman DA (2007). "An ecological and evolutionary perspective on human-microbe mutualism and disease". Nature 449: 811–808. doi:10.1038/nature06245. PMID 17943117. 
  4. ^ Paszkowski U. (2006). "Mutualism and parasitism: the yin and yang of plant symbioses". Curr Opin Plant Biol 9: 364–370. doi:10.1016/j.pbi.2006.05.008. PMID 16713732. 
  5. ^ Isaac 1992, p. 266
  6. ^ Saffo 1993
  7. ^ a b c Moran 2006
  8. ^ Ahmadjian & Paracer 2000, p. 12
  9. ^ Ahmadjian & Paracer 2000, p. 6
  10. ^ Nair 2005
  11. ^ Ahmadjian & Paracer 2000, p. 7
  12. ^ Townsend, Begon & Harper 1996
  13. ^ Wernegreen 2004
  14. ^ Ahmadjian & Paracer 2000, p. 3-4
  15. ^ Brinkman 2002
  16. ^ Golding & Gupta 1995
  17. ^ Sagan & Margulis 1986
  18. ^ Harrison 2002
  19. ^ Danforth & Ascher 1997

[edit] See also

[edit] References

[edit] External links

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