Symbiosis - Definition and examples

In nature all organisms, be they animals, plants or bacteria, create bonds and establish relationships ranging from members of the same family to individuals of different species. We can observe relationships between a predator and its prey, parents and their progeny or interactions that are beyond our understanding with the naked eye..

¿Have you ever heard the word "symbiosis "? In this AnimalWised article, we will see what its meaning is, when we find it in nature and we will show curious examples. ¡Do not miss it!

You may also be interested in: Mutualism in biology - Examples and definition Index
  1. What is symbiosis?
  2. Types of symbiosis
  3. Examples of symbiosis
  4. Endosymbiosis

What is symbiosis?

The word symbiosis in biology was coined by De Bary in 1879. He intended it to be a term to describe the coexistence of two or more organisms that are not closely related in phylogeny (kinship between species), that is, they do not belong to the same species, without the implication of beneficial exchanges per se. Modern usage normally assumes that symbiosis means mutual dependence with a positive result for all those involved.

The association between these individuals must be permanent, they can never be separated. The organisms involved in a symbiosis are called "symbionts " and can benefit from it, be damaged or not obtain any type of effect by the association.

In these relationships, it is often the case that the organisms are unequal in size and very far away in phylogeny. For example, relationships between different higher animals and microorganisms or between plants and microorganisms, where the microorganisms live within the individual.

Definition of symbiosis according to the RAE

To show you in a summarized way what symbiosis is, we also provide you with the definition of the RAE [1]:

1. f. Biol. Association of animal or plant individuals of different species, especially if the symbionts take advantage of life in common.

Types of symbiosis

Before offering you some examples, it will be essential that you know the types of symbiosis that exist:

  • Mutualism. In a mutualistic symbiosis, both parties benefit from the relationship. However, the extent to which each symbiote benefits can vary and is generally difficult to measure. The benefit that a symbiote receives from a mutual association must be considered depending on how much it costs. There is probably no example of mutualism in which both partners benefit equally.
  • Commensalism. Interestingly, this term was described three years before symbiosis. We call commensalism that relationship where one of the parties obtains benefits without harming or benefiting the other. We use the term commensalism in its most extreme sense, where the benefit is only for one of the symbionts and can be nutritional or protective.
  • Parasitism. Parasitism in a symbiotic relationship in which one symbiote benefits at the expense of another. The first factor in parasitism in nutrition, although there may be others: the parasite obtains its food from the organism it parasitizes. This type of symbiosis affects the host in different ways. Some parasites are so pathogenic that they cause disease shortly after entering the host. In some associations, the symbionts have coevolved in a way that does not cause the death of the host (the organism that has the parasite), the symbiotic relationship being much more durable.

Examples of symbiosis

Examples of mutualism:

  • The symbiosis between algae and corals. Corals are animals that grow well in nutrient-poor environments thanks to their symbiotic relationship with algae. These provide them with food and oxygen, while the corals give the algae waste substances such as nitrogen and nitrogen dioxide..
  • The clown fish and the sea anemone. You have surely seen this example many times. The sea anemone (jellyfish family) has a stinging substance to paralyze its prey. The clown fish benefits from this relationship since it obtains protection and, in addition, food, because it frees the anemone of small parasites and dirt on a daily basis, this being the benefit that they obtain.

Examples of commensalism:

  • Relationship between the silver fish and the ant. This insect lives with ants, waits for them to bring food and eats it. This relationship, contrary to what we might think, does not harm or benefit the ants, since the silver fish only eats a little of the food reserves.
  • The tree house. One of the clearest examples of commensalism is one in which an animal seeks refuge in the branches or trunks of trees. The vegetable generally does not obtain any harm or benefit in this relationship.

Examples of parasitism:

  • Fleas and the dog (example of parasitism). This is an example that we can easily observe in our day to day. Fleas use the dog as a place to live and reproduce, in addition to feeding on its blood. The dog does not benefit from this relationship, on the contrary, in addition, fleas can transmit diseases to dogs.
  • The cuckoo (example of parasitism). The cuckoo is a bird that parasitizes nests of other species. When it reaches a nest with eggs, it moves them, lays its own and leaves. When the birds that own the displaced eggs arrive, they do not realize it and raise those of the cuckoo.

Examples of symbiosis in humans:

  • The guide bird of honey and the masai. There is a bird in Africa that guides the Maasai to the hives hidden in the trees. Humans scare away the bees and collect the honey, leaving the bird free to take honey without the threat of the bees.
  • Our relationship with bacteria. Both inside the human intestines and on the skin, there are beneficial bacteria that protect us and help us to be healthy, without them our existence would not be possible.


We cannot finish this article without mentioning this very important fact, by which eukaryotic cells originated (animal and plant cells) and, consequently, life as we know it.

The endosymbiotic theory, In short, it explains that it was the union of two prokaryotic cells (bacteria, for example) that gave rise, on the one hand, to the chloroplasts (organelle responsible for photosynthesis in plant cells) and on the other to the mitochondria (organelles responsible for cellular respiration in both plant and animal cells).

The study of symbiosis has become a scientific discipline in its own right in recent years, and it has been argued that symbiosis is not an evolutionarily fixed relationship, but can manifest itself in many ways, such as commensalism or parasitism. A stable mutualism in which the contribution of each organism involved guarantees its own future.

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