Symbiosis
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Symbiosis (pl. symbioses) (from the Greek words syn = con/plus and biono = living) is an association (relationship) between two organisms (microbes, plants or animals). Normally the two organisms have shared a lengthy period of evolution in close proximity to one another. The term host is usually used for the larger (macro) of the two members of a symbiosis. The smaller (micro) member is called the symbiont (plural: symbionts), or alternately, symbiote (plural: symbiotes). When a microscopic symbiont lives inside the cells of a host, it is referred to as an endosymbiont.
[edit] Types of symbiosis
The various forms of symbiosis include:
- parasitism, in which the association has disadvantages for one of the two. It may even destroy or kill the other. (+ −)
- mutualism, in which the association has advantages for both (+ +)
- commensalism, in which one member of the association benefits while the other is not affected (+ 0)
- amensalism, in which the association has disadvantages for one member. The other is not affected (− 0)
In some cases, the term symbiosis is used only if the association is obligatory and benefits both organisms. Symbiosis as defined in this article does not restrict the term to only the mutually beneficial interactions.
Symbiosis may be divided into two distinct categories: ectosymbiosis and endosymbiosis. In ectosymbiosis, the symbiont lives on the body surface of the host, including the inner surface of the digestive tract or the ducts of exocrine glands. In endosymbiosis, the symbiont lives either in the intracellular space of the host or extracellularly.
[edit] Examples of symbiosis
- An example of mutual symbiosis is the relationship between clownfish of the genus Amphiprion (family, Pomacentridae) that dwell among the tentacles of tropical sea anemones. The territorial fish protects the anemone from anemone-eating fish, and in turn the stinging tentacles of the anemone protect the anemone fish from its predators (a special mucus on the anemone fish protects it from the stinging tentacles).
- 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 of imminent danger. When that happens both the shrimp and goby fish quickly retract into the burrow.
- A famous land version of symbiosis is the relationship of the Egyptian Plover bird and the crocodile. In this relationship, the bird is well known for preying on parasites that feed on crocodiles which are potentially harmful for the animal. To that end, the crocodile openly invites the bird to hunt on his body, even going so far as to open the jaws to allow the bird enter the mouth safely to hunt. For the bird's part, this relationship not only is a ready source of food, but a safe one considering that few predator species would dare strike at the bird at such close proximity to its host.
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