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Symbiosis: the wonder of symbiosis
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Symbiosis
Symbiosis (pl. symbioses) is a close association between two different
types of organisms in a community. It can be defined as:
The living together in permanent or prolonged close association of
members of usually two different species, with beneficial or deleterious
consequences for at least one of the parties.– [1]
There are several classes of symbiosis below. Some of them are antonyms
to positive connotations in symbiosis.
* Mutualism, a relationship in which members of two different species
benefit and neither suffers.'[2] (+ +)
* Commensalism, a relationship in which 'one party gains some benefit,
whilst the other suffers no serious disadvantage'[3] (+ 0)
* Parasitism, in which one member of the association benefits while the
other is harmed (+ -)
* Amensalism, in which the association is disadvantageous to one member
while the other is not affected (− 0). Allelopathy can fall into this
category.
Artificial symbiosis, the mutually beneficial integration between a live
part and an artifact.
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 within
the tissues of the host; either in the intracellular space or
extracellularly.
Examples
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 clownfish from its predators (a special mucus on
the clownfish protects it from the stinging tentacles). Not all anemones
that house clownfish are in need of protection, but this does not rule
out mutualism, as clownfish often share food with their anemone hosts. A
single worm will be halved inside the clownfish's dextrous mouth, and a
portion spit out into the anemone's wavering 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. 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 and are
potentially harmful to them. 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 to 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 proximity to its host.
One of the most spectacular examples of a symbiosis is between the
siboglinid tube worms and symbiotic bacteria that live at hydrothermal
vents and cold seeps. This is a mutualistic symbiosis where the worm
completely loses its 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.
Symbiosis and evolution
The biologist Lynn Margulis, famous for the 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 evolution is strongly based on co-operation,
interaction, and mutual dependence among organisms. According to
Margulis and Sagan (1986), "Life did not take over the globe by combat,
but by networking." As in humans, organisms that cooperate with others
of their own or different species often out-compete those that do not.
References
* Lynn Margulis and Dorion Sagan, Microcosmos: Four Billion Years of
Evolution from Our Microbial Ancestors. Summit Books, New York, 1986.
ISBN 0-520-21064-6
* Jan Sapp Evolution by Association, Oxford University Press, 1994. ISBN
0-19-508821-2
1. ^ Penguin Reference Dictionary of Biology 11th Edition - 2004
2. ^ Penguin Reference Dictionary of Biology 11th Edition - 2004
3. ^ Penguin Reference Dictionary of Biology 11th Edition - 2004
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