What is Symbiosis? Definition, Types and Examples

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What is Symbiosis

The word Symbiosis was coined by Anton de Bary which described about the interaction between two species to exist as long duration relationship. It is a type of a mutualistic relation between two species. When two different species come together in a relation where both of them in the interaction with each other get benefitted is called as Symbiosis. Both the species while living alone did not benefit in any way, thus the interaction of the species together will provide benefit to both of them. Similar to symbiosis there are other types of interactions as well such as Commensalism, Parasitism, Amensalism and others.

History and Etymology of Symbiosis

Symbiosis is a Greek word which means “living together”. It is believed to mean that symbiosis is the interaction of 2 different species. The term coined by Anton said that these relationships between two species can benefit as well as can cause harm to the species.

Later scientist began to explore whether the statement said by the scientist Anton was realistic. They realized that to fulfill the requirement of one and other species, two different species come together as one and stay in a relationship where both of them get benefitted or it could be where one species get benefitted and the other remains unharmed.

An example could be an organism, particularly eukaryotic living in conjunction with other organisms such as virus, archaea, bacteria are called as symbionts, whereas the larger one is called as host, which is the eukaryotic organism in this case.

However, at times to build a relationship, several obstacles are faced such as organelle differentiation which further leads to host and symbiont identification, followed by symbiont engulfment, host’s defense system is damaged, preventing the symbiosis, followed by physiological and genetic integration.

At times when two species stay together in a relationship for too long there are unique features and functions seen due to the evolvement of their relationship. These unique features are more clearly visible when they are in contact for longer duration.

Types of Symbiosis

There are 5 types of symbiosis and are:

a) Mutualism

One of the most common type of symbiosis is the mutualism. In mutualism, both the species get benefitted during the interaction. Although it could have an impact on the upcoming population and its survival. In such type of interaction, evolution takes place as they stay in conjunction to each other. Lichens are the example of mutualism.

Another example could be the relationship between algae and fungus, where fungus will provide support and protection and in return gets food from the algae, due to the photosynthetic pigment. Rhizobium legume symbiosis and arbuscular mycorrhizas are some examples of mutualism.

b) Commensalism

In this type of interaction one of the species gets benefitted while the other remains unharmed. This type of relationship is seen in organism found in the soil, where one organism provides the necessary requirements to the others.

Example of this type of interaction is when an organism produces antibiotic towards a pathogen, while protecting the plant. Bacillus and Pseudomonas are known to have such properties.

Another example in animals is remoras and sharks. To attract the prey towards itself remoras has a disk on which fishes such as bony fishes, sea turtle and others attach. Interaction between remoras and sharks make transportation, protection from preys possible to the shark and these remoras feed on small animals, zooplankton and host’s fecal matter.

c) Amensalism

In this type of interaction one species has a negative impact on the other, while the other species is hardly affected. Mussel beds incapacitates various species is an example of amensalism. Another example is taller plants which covers the shorter plant, thus the light reaching the shorter plant is very minimal or no light.

d) Parasitism

The relationship involving no mutual benefit is called as Parasitism. Majority of the species on earth are parasites. Example vampire, bats, nematodes, flatworms and etc. parasitism is the interaction where the parasite is dependent on the host to meet its requirement. Although the parasites are smaller than the host but they do not kill them instead feed on them. An example is tropical ants and a roundworm. Other example are tapeworms and fleas.

e) Predation

In this type of a relation, one species get rids of the other by killing them. In simple words the symbiont kills the host. An example of this interaction is sea anemone which are the host and the symbiont is the hermit crab.

Examples of Symbiosis

There are various example of symbiosis and they are:

a) Mycorrhizas

This is a very common type of interaction seen between plants and fungi. The fungi will form the arbuscular mycorrhizas (AM) and these fungi require host to outgrow, without the host they cannot grow. Thus, here one of them get the required nutrients whereas the other benefits from disease and drought occurrence.

Symbiosis, 1 What is Symbiosis, Symbiosis Types, Symbiosis Examples
b) Pinworm

Enterobius vermicularis, pinworm is the nematode causing infection to humans. This pinworm is an example of parasitic symbiotic relationship. These infections are seen in infants who are able to poop properly. The adult pinworms are found in the intestine and grow about a size of 1cm in size and these female adults come out of the host during the night move out and release eggs on the perianal skin. Within few hours the lifecycle of this worm is completed as the eggs are hatched and releases the infected larvae in the small intestine.

c) Amebiasis

This is a very dangerous issue in the countries developing due to the parasitic infection leading to major mortalities. The humans are the host and the protozoans interact with the host to slower the pace or fasten the disease. In children’s it causes diarrhea leading to death in various developing countries. When an infant is born, 1 out of 30 infants die every day due to diarrhea in developing countries like Bangladesh. The protozoan behind the disease is Entamoeba histolytica causing dysentery. However, other microorganism can also affect the interaction. When Entamoeba was cultured with other deadly bacteria, the effect of entamoeba might have increased or diminished.

d) Clownfish and Sea Anemones

There are various species which interact with sea anemones in various symbiotic relationship. However, the most commonly studied is the Clownfish. The interaction between the clownfish and the sea anemones is a mutualistic symbiosis one. Clownfish will deliver host with carbon, nitrogen and oxygen whereas the sea anemone will provide nutrition and protection. Thus, staying together and mutually get positively affected.

e) Oxpeckers and Mammals

In order for oxpeckers to adapt itself to various climates and conditions other mammals helps oxpeckers and are as follows: to hide they have sharp claws that helps in clinging. To support the oxpeckers, it has long tails. This relation is beneficial to both the species as oxpeckers have beaks which is sharp and flattened to catch ticks serving food to the others.

f) Black Walnut Tree

In amensalism, there is competition as well and its example is the Black walnut tree. This plant gathers harmful chemicals after it has aged to 25 years of age and does not allow any other plant to grow near it. The chemical behind this behavior is juglone, thus competing from the other plants.

g) Rhizobium Legume

For plants, nitrogen is very vital. Although it is available in the environment but its in the form that cannot be used and eukaryotes do not have the machinery to convert inert nitrogen into the required for. Thus, different relationship have been employed between diazotrophic bacteria and eukaryotes. Nitrogen fixing bacteria, Rhizobium is capable of fixing nitrogen. Thus, many species have thought to come in conjunction with the rhizobacteria. In exchange one gets the nutrition required whereas the other gets the fixed nitrogen.

h) Crabs and Sea Urchins

In the Indo-West Pacific region is a crab called Echinococcus pentagonus. These adults reside in the sea urchin’s rectum. Thus, they get food and shelter from sea urchin, whereas the younger ones and the males freely move on the surface. This type of relation can be considered as commensalism as well as parasitism because they do not kill their host.

i) Human gut Microbiota

Humans and microorganisms have a direct relation. The human gut is huge and inhabitates various microorganism, commonly known as gut microbiota. It is a symbiotic relationship because these microorganisms get shelter and in return, they break down food and provides human energy. However, this microorganism could also turn opportunistic and cause diseases. If these microorganisms are present at unnecessary places could cause major damage in humans.

j) Viruses

Virus also requires host to completes its role. They are parasites which completes its lifecycle by replicating and infecting. A virus can be mutualistic where both of them benefits or even parasitic or a commensal where one benefits and other is unharmed. There are cases where organism requires virus such as polydnavirus and wasps.


Thus, we can say that symbiotic relationships can be seen various categories and types of species. Species lives in symbiosis for various reasons as we know to obtain, shelter, nutrition, to feed on the other one and various others reasons.

A term called “Holobiont” was later discovered in 1991 by Lynn Margulis which meant a relation between the symbiont and the host, which was later stretched to determine the interaction between the host and various microorganisms. A holobiont comprises of microbiota and the host. A holobiont constitutes of all the interactions and is been studied in various fields of plants, animals and humans.

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