Symbiosis

Symbiosis (from the Greek σύν sýn together ' and βίος bios ' life' ) called in Europe the socialization of individuals of two different species which is beneficial for both partners.

Based on his work on lichens Anton de Bary in 1878 struck at the 51st General Assembly of German Natural Scientists and Physicians in Kassel before, the term symbiosis for any coexistence of dissimilar organisms, so also for the parasitism of introducing into the biology. In this broad sense, the term symbiosis (English symbiosis ) is still used in the U.S. literature for all forms of coevolutionär resulting coexistence of mutualism over neutralism up to parasitism. In Europe, the term symbiosis, however, for the above-defined narrower term was used.

In symbiosis between organisms that differ considerably by their size, referred to the larger partner often as the host, the smaller as a symbiont.

Frequency of symbioses

Most of the biomass on the ground consists of symbiotic systems because a large portion of the trees and bushes depends on other species pollination. Then there are the lichens, a symbiotic community of life between a fungus and green algae or cyanobacteria. Many living in shallow water sessile marine invertebrates such as fire coral, most anemones and giant clams live together with photosynthesis operated zooxanthellae. Another example is the gastro- intestinal bacteria of the animals such as in ruminants allow the digestion of cellulose -rich plant food.

Distinction on the degree of interdependence

A possibility of distinguishing different forms of symbiosis results from the degree of interdependence of the species involved:

• Proto cooperation (Alliance): loosest form of symbiosis: both species, although take advantage of the coexistence, but without each other nevertheless viable.
• Mutualism: Regular, but not vital relationship of the symbionts.
• Eusymbiose, even obligatory symbiosis (from the Greek eu, " good", " true" ): When Eusymbiose are the partners alone are no longer viable. So cultivate leaf-cutting ants in their construction fungi, of which they feed; the fungi in turn can not reproduce without the ants.

Discrimination on the basis of the spatial relationship

A distinction between different forms of symbiosis results from the spatial or physical relationship of the two species involved:

• Ektosymbiose: a partner in a symbiosis remain physically separated (about flowers and their pollinators; Clown fish and sea anemones her );
• Endosymbiosis: one of the partners is included in the body of the other ( such as certain enteric bacteria in the intestines of humans and animals; nodule bacteria in the roots of leguminous plants, zooxanthellae in reef-building corals of the tropical belt ). The endosymbiotic theory states that eukaryotes are caused by the fact that prokaryotic precursor organisms have entered into a symbiosis.

Distinction according to the type of benefits achieved

A distinction of symbiosis forms arises due to the nature of the benefits achieved for the two species involved.

• Reproductive symbiosis: An example of reproductive symbiosis is the symbiotic relationship between bees and flowering plants. The bee takes the nectar of flowers on as food, while the pollen of flowering stick to it, which then transfers the bee and thus a different flower pollinated, so it can multiply. This is called bestiality and is the " normal" act of pollination of flowering plants ( angiosperms ) by insects or birds, the insects or birds nectar, but also pollen as a food.

• Symbiosis for protection from enemies: An example of this symbiosis is the relationship of ants to aphids. The ants enter the aphids protection from enemies, in return these can be from the ants " milk ," she but a sugar solution from taking the ants themselves.

Other examples

• ( Called animal scattering) transport of plant seeds by animals, where animals eat the fruits and excrete the seeds to another location ( Zoochorie ) or the seeds temporarily attached to animals.
• Lichens consist of fungi and algae, the algae produce carbohydrates by photosynthesis, which are absorbed by the fungi while the fungi provide the algae water and nutrient salts.
• Ants protect aphids, which they receive in return from these sugar water. In some ant species, such as the leaf-cutter ants veritable mushroom farms are created within the Ameisenbauten in which certain fungi are fertilized with plant residues and purified from spores of harmful fungi. Parts of the fungi the ants serve as food. This symbiosis is called Myrmekophilie form.
• Mycorrhizal fungi evade trees or other photosynthesizing plants carbohydrates and provide in return minerals and water from the soil. Mycorrhiza is mandatory for all orchids, but also for many other plant species.
• The skin parasites of large mammals (eg, hippo and elephant) are eroded by Putzer birds, the same phenomenon can be found at cleaner fish that attach themselves to large fish (eg sharks) and parasites from their skin erode (→ cleaning symbiosis ).
• In Yellowstone National Park in North America, a symbiosis between three types was detected, a bluegrass, a fungus and a virus. There are many hot springs in the area and the ground is heated up. The grass Dichanthelium lanuginosum tolerated due to a symbiosis with the fungus Curvularia protuberata in the root zone to temperatures of nearly 70 ° C. Both the fungus alone and the grass alone can only approximately 38 ° C survive. Absolutely necessary in this symbiosis is the third party, the virus CthTV, ( Curvularia thermal tolerance virus) that infects the mold. If this virus is removed, the mold loses its heat resistance, and with it perishes even the grass on the hot locations.
• Sulfide-oxidizing chemoautotrophic bacterial endosymbionts within the cells of polychaetes or between the cells of oligochaetes as well as ectosymbionts on the surface of single-celled colonies as niveum Zoothamnium. You will get through this life optimum conditions within the sulfide-rich environment at hydrothermal vents like the black smokers of the deep sea or in the vicinity of decaying organic matter in the shallow water and digested by their hosts partially. This symbiosis (eg, Riftia ) so closely with the beard worms, that the animals in the adult state, have no mouth and absorb any external food more.
• Hermit crabs live occasionally in symbiosis with a sea anemone that has ended up on its housing: The sea anemone protects the hermit crab from predators; "transported" the hermit crab, the sea anemone to new feeding grounds, also gets the anemone from something from the booty of the hermit crab.
• Plants can take up endophytic bacteria, such as nasturtiums.

Endosymbiontentheorie

The endosymbiotic theory states that mitochondria and chloroplasts, organelles in eukaryotes (plants, animals and fungi), at an early stage of evolution of endosymbiotisch living prokaryotes (aerobic, bacteria or cyanobacteria chemotrophe ) have emerged. This is supported by the similarities in the structural design and the characteristics deviating from the host cells, but coincident with the prokaryotes, biochemical (eg structure of the ribosome and, where available, of the DNA). Furthermore, these proliferate cell organelles, bacteria do by division, just like it.

Symbiogenesis

The inclusion of endosymbionts is an example of that symbiotic communities in the course of evolution can be so tight that it makes sense to consider these biological species formed as new. This emergence of a new kind of fusion of symbionts is called symbiogenesis. The importance of symbiogenesis has been strongly emphasized in recent times by the American evolutionary biologist Lynn Margulis. After their (highly controversial ) theory symbiogenesis one of the main mechanisms artbildenden at all.

Scientific description

The scientific description and modeling of symbiotic systems are used in biology systems of ordinary differential equations, but occasionally complicated mathematical structures used.

For example, with the aid of some idealized simplifications symbioses of two species at the level of population dynamics described by:

If an effect of a change in the symbiosis in intrinsic growth rate of the population is involved

And

If the primary effect is an adjustment of capacities.

( Designations: X, Y abundances of species and a, b intrinsic growth rates of the species, K1, K2 capacity cd ecological interaction parameter )

A mixture of both simplistic limiting cases are of course possible, and may be regular way suspected in nature.