Any of several living arrangements between members of two different species, including commensalism, mutualism, and parasitism. The species involved are called symbionts. In commensalism, one species (the commensal) obtains nutrients, shelter, support, or locomotion from the host species, which is substantially unaffected (e.g., remoras obtain locomotion and food from sharks). In mutualism, both species benefit. Many mutualistic relationships are obligative; neither species can live without the other (e.g., protozoans in the gut of termites digest the wood ingested by the termites).
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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".
The definition of symbiosis is in flux 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 . Others define it more narrowly, as only those relationships from which both organisms benefit, in which case it would be synonymous with mutualism.
Symbiotic relationships included those associations in which one organisms lives on another (ectosymbiosis, such as mistletoe), or where one partner lives inside another (endosymbiosis, such as lactobacilli and other bacteria in humans or zooxanthelles in corals). Symbiotic relationships may be either obligate, i.e., necessary to the survival of at least one of the organisms involved, or facultative, where the relationship is beneficial but not essential to survival of the organisms.
Endosymbiosis is any symbiotic relationship in which the symbiote lives within the tissues of the host; either in the intracellular space or extracellularly. Examples are nitrogen-fixing bacteria (called rhizobia) which live in root nodules on legume roots, Actinomycete nitrogen-bacteria called Frankia which live in Alder tree root nodules, single-celled algae inside reef-building corals, and bacterial endosymbionts that provide essential nutrients to about 10%–15% of insects.
Ectosymbiosis, also referred to as exosymbiosis, is any symbiotic relationship in which the symbiont lives on the body surface of the host, including the inner surface of the digestive tract or the ducts of exocrine glands. Examples of this include ectoparasites such as lice, commensal ectosymbionts, such as the barnacles that attach themselves to the jaw of baleen whales, and mutualist ectosymbionts such as cleaner fish.
The term Mutualism describes any relationship between individuals of different species where both individuals derive a fitness benefit. Generally only lifelong interactions involving close physical and biochemical contact, can properly be considered symbiotic. Mutualistic relationships, may be either obligate for both species, obligate for one but facultative for the other, or facultative for both. Many biologists restrict the definition of symbiosis to close mutualist relationships.
A large percentage of herbivores have mutualistic gut fauna that help them digest plant matter, which is more difficult to digest than animal prey. Coral reefs are the result of mutualisms between coral organisms and various types of algae that live inside them. Most land plants and land ecosystems rely on mutualisms between the plants which fix carbon from the air, and Mycorrhyzal fungi which help in extracting minerals from the ground.
Another example is the goby fish, which sometimes lives together with a shrimp. The shrimp digs and cleans up a burrow in the sand in which both the shrimp and the goby fish live. The shrimp is almost blind leaving it vulnerable to predators when above ground. In case of danger the goby fish touches the shrimp with its tail to warn it. When that happens both the shrimp and goby fish quickly retract into the burrow.
One of the most spectacular examples of obligate mutualism is between the siboglinid tube worms and symbiotic bacteria that live at hydrothermal vents and cold seeps. The worm has no digestive tract and is solely reliant on their internal symbionts for nutrition. The bacteria oxidize either hydrogen sulfide or methane which the host supplies to them. These worms were discovered in the late 1980s at the hydrothermal vents near the Galapagos Islands and have since been found at deep-sea hydrothermal vents and cold seeps in all of the world's oceans.
Commensal relationships may involve an organism using another for transportation (phoresy), for housing (inquilinism), or it may also involve an organism using something another created, after the death of the first (metabiosis). An example is the hermit crabs that use gastropod shells to protect their bodies. Further examples include spiders building their webs on trees.
While historically, symbiosis has received less attention than other interactions such as predation or competition, it is increasingly recognised as an important selective force behind evolution, with many species having a long history of interdependent co-evolution. In fact the evolution of all eukaryotes (plants, animals, fungi, protists) is believed to have resulted from a symbiosis between various sorts of bacteria.
Probability of Symbiosis Establishment by Giant Clams with Fresh and Cultured Symbiodinium Isolated from Various Host Animals
Dec 01, 2012; ABSTRACT Giant clams need to establish a symbiotic relationship with the microalgae Symbiodinium in the environment to survive...