Symbiosis: what is it, types and characteristics of this biological phenomenon?

Let's see what symbiosis is and how it occurs in living beings of different species.

In the world, there are a total of 8 types of ecosystems or biomes that are home to the different species of living beings that inhabit today. To understand an ecosystem, it must be taken into account that it is made up of two major elements: the biotope and the biocenosis.

The biotope refers to an area of specific environmental conditions that provides a vital space for the flora and fauna. That is, the physical environment (rocks and sediment, among others), the availability of water, environmental parameters, geographical features and other non-living elements. On the other hand, biocenosis corresponds to the set of populations of living beings that coexist in space and time. Thus, living matter is as essential in an ecosystem as the scenario in which it develops.

If we look at the biocenosis, we can describe an infinite number of intra- and interspecific interactions. You should bear in mind that 1,426,337 animal species have been described, so there is room for all kinds of interaction between them: predation, direct and indirect competition, parasitism, commensalism and symbiosis, among others. Today We focus today on this last type of biological interaction, symbiosisbecause sometimes there is strength in unity.

What is symbiosis?

As with any scientific term, the etymological root of the same one will allow us to know its meaning. The word symbiosis comes from the Greek word σύν, syn (together) and βίωσις, biosis (to live). Thanks to this linguistic dissection, we can imagine where things will go from here.

The term symbiosis applies to the close and persistent relationship between organisms of different species, where the parties involved in this interaction are known as symbionts.. However, it is necessary to make a few definitions before continuing to dissect the symbiotic phenomena.

In its broadest and loosest sense, the term symbiosis is defined as any type of biological interaction between species, whether beneficial or detrimental to either party. Thus, paradoxically, parasitism would be a type of negative symbiosis, since both elements are highly related to each other and co-evolve at the same time, although one of them is severely harmed over time (the host). This definition would also include commensalism, an interaction in which one party benefits and the other is indifferent.

At a popular level, symbiosis is often associated indistinctly with mutualism.. In this case, the relationship between the members must be positive for both, so parasitism and commensalism are left out. Finally, some authors use an even stricter meaning of the term, where it is required that the relationship be indispensable for the life of both species. Although in mutualism both parties benefit, they can continue their lives separately. In the more classical symbiosis, the components cannot survive without the action of the other.

Types

Symbiosis can be classified into different types, but here are the most important ones.

For example, if we look at the spatial relationship between the two participants, there is a possible ectosymbiosis and an endosymbiosis.. In ectosymbiosis, as the name implies, one of the members lives on or around the body of the other. Crabs and anemones, for example, may come to mind, since these crustaceans live on them to protect themselves and, at the same time, prey on possible parasites that settle on the anemone.

On the other hand we have endosymbiosis, which cannot be seen externally but is equally (or more) important at the evolutionary level.. In this case, one of the individuals lives inside the other, so it must necessarily be smaller than the other (we generally speak of microorganisms). The intestinal microbiota and the human being are a clear example of this: many of our bacteria could not live outside our Gastrointestinal tract, and at the same time they help us to digest substances, specialize the immune system and avoid infections, among other things.

Based on other parameters, symbioses can be either facultative or obligatory. These terms are fairly well explained quickly: in the first case, both elements can live on their own but benefit from the interaction, while in others the life of one cannot be conceived without the other. A very curious case of facultative symbiosis is that of certain birds on the backs of large mammals: the birds deworm oxen and rhinoceroses (among others), worming them, but if there is no food, they forage for it themselves.

On the other hand, a clear example of obligate symbiosis are lichens.The lichen is the product of a close evolutionary union between a fungus and an alga or cyanobacterium. The alga is capable of photosynthesis, so it provides the fungus with organic matter without much difficulty. On the other hand, the hyphal structure of the fungal element captures water and mineral salts from the environment, thus defending the alga from drying out, no matter how dry the environment may be. In this case, neither of the 2 elements survive in the environment without the other.

Degree of symbiosis in living things.

Another way to understand symbiotic processes in living beings is to place on a numerical scale the level of interaction between the participants. Based on this parameter, we can create the following list or ranking:

Degree of least interaction 2.

The members establish a behavioral relationshipThe members establish a behavioral relationship, i.e., they live together, seek each other out and have learned to interact in a positive way.

2. Metabolic degree

This is the case of lichens. Generally, in these cases the exudate or metabolic product of one of the members is the food of the other.

3. High degree of interaction

For example, the proteins of one of the members of the symbiosis is indispensable for the other. This is the case for many plants.

4. Highest degree of integration

There is a a transfer of genetic material and the consequent fusion of the symbionts, thus generating a new living being where before there were 2.

Symbiosis or altruism?

It is very common for us to humanize the rest of living beings, because we believe that they are governed by the arbitrary moral and ethical codes we have established. Nothing could be further from the truth. In nature, nothing is done at random or out of disinterest, at least in the vast majority of animals.

Thus, a symbiosis can be ruined throughout the evolutionary history of both species if it ceases to bring benefits to either party. As soon as one of the species begins to "lose" in the relationship, the mechanism is destabilized and problems may arise, even leading to parasitism.and even lead to phenomena of parasitism. Here is an example.

A clear case that exemplifies the above is that of the oxpeckers, 2 species of birds belonging to the family Buphagidae. These cute little black birds perch on the backs of large mammals and, symbiotically, extract insects and parasites that settle on their skin. So far, both participants are clearly benefiting, right?

What happens is that these birds love blood, and so they have a predilection for the swollen ticks present on the mammal's surface. When there aren't enough of them or the bird needs extra caloric intake, it sometimes takes it upon itself to hold the wound open and suck it directly from the host. Where once there was symbiosis, a line has been crossed into parasitism..

Summary

As we have seen, the term "symbiosis" is more nuanced than one might at first expect. In nature, not everything is black and white, as biological systems are influenced by the environment and can change at any time. When one species ceases to be of benefit to another, in the best case one of the members separates, and in the most extreme case, the dominant one subjugates the other and either preys on or parasitizes it.

The term "empathy" does not clearly exist in most members of the animal kingdom, and phenomena such as these exemplify it perfectly. For living beings, the only thing that matters is the transmission of genes and the permanence of their species, at whatever cost and detriment is necessary. Undoubtedly, nature is as beautiful and fascinating as it is cruel.

Bibliographic references:

• Bleger, J. (2020). The symbiosis.
• Cañizares, P. J. G. (2015). Effective management of arbuscular mycorrhizal symbiosis via inoculation and mineral fertilization in grasses of the genus Brachiaria. Editorial Universitaria.
• Durán-Alvarado, F. J. (2003). Foraging of the tufted magpie, Calocitta formosa (Aves: Corvidae), on white-tailed deer Odocoileus virginianus (Mammalia: Cervidae). Brenesia, (59/60), 89-90.
• Hawksworth, D. L. (1989). Fungal-algal interactions in lichenoid and lichenoid symbioses. In Annals of the Botanical Garden of Madrid (Vol. 46, No. 1, pp. 235-247). Royal Botanical Garden.
• Rivera, R., Ruiz, L., Fernández, F., Sánchez, C., Riera, M., Hernández, A., ... & Planas, R. (2006, March). Effective mycorrhizal symbiosis and the soil-plant-fertilizer system. In Congreso Sociedad Cubana de la Ciencia del Suelo (6: 2006 Mar 8-10: Havana). Proceedings [CD-ROM] Havana City: Capitol Convention Center.