SYMBIOSIS: TYPES, CHARACTERISTICS AND EXAMPLES IN NATURE - BIOLOGY - 2025

The symbiosis or symbiotic relationships is the interaction between two organisms of different species that are tailored to specific ecological conditions for mutual benefit. The German botanist Heinrich Anton de Bary pioneered the study of these interrelations, introducing the term "symbiosis" in 1879.

Therefore, the individuals that interrelate in the process are known as symbionts. If there is a significant difference in size, the largest will be called the host, and the smallest symbiont.

Lichens are a symbiosis between a fungus and an alga. Source: pixabay.com

In an ecosystem totally isolated organisms do not coexist in their environment. All maintain some type of interaction with other species to satisfy their own needs or together.

Indeed, these relationships do not occur at random, but are the result of an evolutionary process between species. In this regard, symbiotic relationships have different effects on each individual, hence their definition and classification.

The symbiosis aims to satisfy a need by one or both participating organisms. Depending on the integration of this relationship, the most common types of symbiosis are defined: mutualism, commensalism and parasitism.

characteristics

In mutualism, both organisms gain a benefit, while in commensalism only one of the organisms benefits. On the contrary, in parasitism one of the organisms takes advantage of the other, causing it a particular damage.

These symbiotic relationships occur at all trophic levels of terrestrial and aquatic ecosystems. In fact, it is common to observe these relationships at the intracellular level, where organelles interact with each other to fulfill certain functions.

In this context, it is common to find examples of symbiosis in most living beings on the planet; animals, plants, fungi and microorganisms. Lichens, formed by a symbiotic relationship between an alga and a fungus, was one of the first interactions studied.

At the microscopic level, symbiotic relationships have a great influence on health issues and agricultural production. Many microorganisms can become pathogens of plants and animals, including man, causing diseases that are difficult to control.

At present, knowing the mechanisms that govern symbiotic relationships is the subject of study in Biology. To know how this phenomenon has evolved is to understand how nature maintains life on planet Earth.

Types

A general classification of the way organisms interact is based on their physical interaction. In this regard, the physical space where the symbionts interact is delimited, inside the body or outside.

• Endosymbiosis: it is the symbiotic association where an individual lives inside the other individual. For example: the bacterial flora that is part of the intestinal tract of mammals.
• Ectosymbiosis: it is the interaction where one of the symbionts interacts with the other individual. For example: the relationship between bees and flowers during the pollination process.

When the interaction is essential to maintain the vital capacities of one of the symbiotes, we speak of permanent or mandatory relationships. Otherwise, the relationships are called temporary or optional.

Likewise, depending on the way in which the symbiotic process begins, there are vertical transmission and horizontal transmission relationships. In the vertical the symbionts are transferred to the offspring, and in the horizontal the host obtains the symbionts from the environment.

In effect, the correspondence in obtaining a benefit is the way in which symbiotic relationships are mainly classified, taking into account that this benefit can be shared, directional or become detrimental to one of the symbionts.

Mutualism

It is the interaction in which both symbionts obtain a common benefit for the individual survival of each species. When beneficial interactions occur between organisms of the same species, the relationship is called cooperation.

Mutualism has been used as a synonym for symbiosis, however, symbiosis must be necessary for the benefit of both species. On the contrary, mutualism is not necessary for each species to survive independently.

This interaction can be temporary or facultative, when both species benefit, however, they can survive without the interaction occurring. In the permanent or forced mutualism, the interaction is totally dependent, the organisms cannot survive without the presence of the other.

Indeed, mutualism constitutes one of the most widely distributed symbiotic relationships on the planet, from mammals to microorganisms. Studied not only at a biological level, but at a sociological level, due to the interactions that occur between species in their various habitats.

In mutualism, an interaction occurs where a resource or service is obtained as a benefit. In this way, mutual relations are based on the exchange of resources (nutrients) and services (protection) for the benefit of both symbionts.

Types

An example of a mutualistic relationship where both symbionts obtain a resource occurs in the mycorrhiza of plants. In the interaction between soil fungi and plants, the fungus provides nutritional elements and obtains carbohydrates.

In the case of species that provide and obtain services in their mutualistic relationship, there is the anemone and the clownfish. The fish protects the anemone against its natural enemies, and the anemone provides a place of protection for predators.

The relationship between bees and flowers constitutes a type of mutualism where a service is exchanged for a resource. The bees obtain the nectar from the flowers and the flowers manage to disperse their pollen thanks to the intervention of the bees.

Mutualism is a symbiosis where the individuals involved participate in a win-win relationship. In an example of how the relationships between species have evolved to complement their way of life in a particular environment.

Commensalism

Commensalism is an interaction between individuals of two species in which one species benefits. However, the individuals of the other species do not obtain any benefit, nor are they harmed by this relationship.

Scavengers

In nature, this type of interaction is common between species that feed on the waste of other species. The so-called scavenger species, such as hyenas or vultures that feed on the waste of carnivorous animals.

Foresis

The commensal interaction where one species obtains transport and protection from another is called phoresis. Remora fish adhere to the surface of the shark, obtaining the surplus food and transporting them to other underwater territories.

Tenancy

In tenantism, a species stays and lives within another species, obtaining protection and shelter. Woodpeckers make a hole with their beak in various tree species, obtaining food and shelter without harming the tree.

Metabiosis

Finally, metabiosis is a relationship where one species benefits from the physical remains of another as a tool. An example is the hermit crab, which protects its fragile body by inserting itself inside the snail shell.

Parasitism

Parasitism is the interaction between individuals of two species in which one species benefits to the detriment of the other. In this case, the individual who benefits is called a parasite, and the one who is affected is the host.

Depending on the habitat where the parasite interacts with the host, the parasites can be endoparasites or ectoparasites. The endoparasite lives inside the host, and the ectoparasite lives outside the host.

Through parasitism, many species have evolved supplying their vital needs at the expense of a host. The species that parasitizes is capable of supplying its nutritional needs, habitat and security, causing damage to the host.

Indeed, in the parasitism relationship, the host never gets a benefit, it is a lose-lose relationship. The host tends to diminish its vital capacities, dying as a result of interaction with the parasite.

A characteristic of parasites is their high ability to dominate other species. In this regard, they are organisms adapted to extreme conditions and endure sudden changes resulting from the defense mechanisms of the host individuals.

Examples of endoparasites are viruses, amoebas, or worms that live within a host at the expense of its nutritional capabilities. Externally, fleas, mites, ticks or termites are examples of ectoparasites.

Importance

In diverse terrestrial and aquatic ecosystems, organisms associate in symbiotic relationships to share and compete for resources. Symbiosis is present in all vital activities, being a frequent phenomenon for the survival of most species.

Symbiosis constitutes a mechanism that strengthens the evolution of species. Through symbiotic relationships, many organisms manage to expand their vital capacity in various ecosystems and environmental conditions.

Examples in nature

There are numerous examples of symbiotic relationships that are achieved in nature. Below is a group of interactions that reflect the way different species interact to achieve survival in their natural environments.

Lichens

Lichens represent a mutualistic symbiotic interaction between an alga and a fungus. In this interaction the fungus is the dominant species, the mycobiont; the other species, which can be an alga or a cyanobacteria, is the phycobiont.

In this interaction, the fungus constitutes the support of the alga, providing structure and moisture. Likewise, the alga is responsible for producing carbohydrates that it shares with the fungus to complete the symbiotic association.

Lichen. Source: pxhere.com

Mycorrhizae

Mycorrhizae are a mutualistic symbiotic interaction between various soil fungi and plant roots. Soil fungi, such as the phyla Glomeromycota, Basidiomycota and Ascomycota, establish themselves in the rhizosphere of the plant exchanging nutrients.

In this relationship, the plant benefits by having at its disposal various nutritional elements that have been decomposed by fungi. Likewise, the interaction between the roots and the mycelium of the fungus allows them to take advantage of a greater volume of soil.

In the case of the fungus, it obtains a living space and absorbs carbohydrates produced in the photosynthetic process. The success of mycorrhizae depends on the environmental conditions where the symbiosis develops.

Interaction of mycorrhiza in the rhizosphere of the crop. Source: pixabay.com

Intestinal Flora

The intestinal flora is a symbiotic relationship that exists between a group of bacteria and microorganisms within the intestinal tract of mammals. The microflora is composed of thousands of beneficial bacteria that display functions in the body.

The various bacteria that make up the intestinal flora perform nutritional, protective and immunological functions. However, they are easily altered by simple dietary changes, medications, viral infections, or age.

Intestinal flora. Source: pxhere.com

Ants and aphids

Some species of ants and aphids or aphids maintain a type of symbiotic relationship of the mutualistic type. In this relationship, the aphid receives protection and care from the ants, which benefit from the sweet nectar that the aphid produces.

Ants (Tetramorium) protect aphids (Paracletus cimiformis) like a herd by establishing a cooperative relationship. In this relationship the aphids get protection and the ants food.

Ants and aphids. Source: pxhere.com

The clown fish and the anemone

The colorful clownfish (Amphiprion ocellaris) inhabit poisonous anemones at the bottom of the sea. Establishing a mutualistic relationship, where the clownfish attracts predators that are paralyzed by the poisonous tentacles of anemones.

Once the predatory fish are paralyzed, they serve as food for the anemones. The remains are used by the clown fish, which in this task manages to clean and keep the water around its host oxygenated.

Clown fish and anemone. pixabay.com

Sharks and remoras

The symbiosis between sharks and remoras (family Echeneidae) is a clear example of commensalism. Although remoras are excellent swimmers and are capable of hunting, they prefer to attach to sharks for transportation and food.

Symbiotic relationship between shark and remora. Source: pxhere.com

Crocodiles and plovers

The crocodile and the pluvial or Egyptian plover maintain a relationship of mutualism. Despite the fact that the crocodile has a jaw with more than 80 sharp teeth, it is not inconvenient for the bird to walk freely between its jaws.

In effect, the relationship is established in the bird's need for food and the reptile's hygiene requirement. The plover gets its food by cleaning the remains of food from the crocodile's mouth and it gets cleaning between its teeth.

Crocodiles Source: pxhere.com

References

1. Fernández, AR, & Cordero del Campillo, M. (2002). Parasitism and other biological associations. Parasites and hosts. Veterinary Parasitology, 22-38.
2. Hilje, L. (1984). Symbiosis: Terminological and evolutionary considerations. Uniqueness, 1 (1), 57-60.
3. Ingraham Jhon L. & Ingraham Catherine A. (1998) Introduction to Microbiology. Editorial Reverté, SA Vol. 2. ISBN 84-291-1871-3
4. La Peña-Lastra, D. (2017) Mutualism vs. parasitism. Micolucus, 61.
5. Interspecific Relations (2003) "Roberto Beltrán Neira" Faculty of Stomatology, Universidad Peruana Cayetano Heredia. Recovered in: educarchile.cl
6. Stainer Roger Y., Ingraham Jhon L., Wheelis Mark L. & Painter Page R. (1992) Microbiology. Editorial Reverté, SA Second Edition. ISBN 84-291-1868-3