NEUTRALISM (BIOLOGICAL RELATIONSHIP): THEORIES AND EXAMPLES - BIOLOGY - 2024

The neutralismo in ecology is a relationship or interaction between two biological entities, in which no party is favorably or unfavorably affected. According to various authors, relationships of this type are virtually impossible in nature. Species are exposed to extremely complex relationships, so a neutral relationship is quite difficult to prove.

In the vast majority of interactions, the participating species are affected in one way or another. There are two more models, commensalism and amensalism, which propose neutrality for one of the participating species, and the other will have a positive or negative effect - respectively.

Source: NIAID, via Wikimedia Commons

Empirical studies have been few, since there are experimental difficulties to prove that the interaction has no effect. However, it is proposed that the interaction between bacteria of specific genera has no effect on them.

Biological relationships

Ecological communities are defined as the set of populations that live at the same time in a common area.

These communities are shaped by a network of complex and dynamic interactions. The relationships that occur between individuals can be classified into two fairly broad categories: direct or indirect.

Direct relationships

As the name implies, direct effects occur when the interaction per se has an effect on the fitness of the individuals involved in the process, without the need for a third party. For example, a hummingbird pollinating a flower is an example of a direct interaction between two species.

Ecologists typically classify such direct interactions into eight types, depending on the effect of the relationship - whether it is positive, negative, or neutral: mutualism, commensalism, predation, herbivory, parasitism, amensalism, competition, and neutralism.

The interaction discussed in this article, neutralism, implies that the relationship has no effect on any of the species involved in that interaction. However, most of the literature agrees that this phenomenon is rare and unlikely.

In many cases, the effect is neutral in one of the species, while in the other individual involved in the process, the interaction can have positive or negative results. We will now discuss these types of interactions that are made up of a “neutral” portion.

Commensalism

In commensalism, for example, one of the organisms is positively affected by the interaction, while the second is unaffected. Relationships of this type are considered long-lasting and stable. Some microorganisms benefit from growing in a host, in which they have no effect.

In fact, most of our biota is considered commensal organisms. Although individually they do not produce benefits, collectively they prevent - through competition - pathogenic organisms from developing.

Furthermore, certain microorganisms that were previously considered "commensals" have been shown to actually have a positive effect on the host - such as vitamin synthesis.

In the case of plants, there are certain seeds that need to germinate in desert environments with very high temperatures and can only do so under the shade of other plants.

In this case, the organism that will develop from the seed is benefited, but the surrounding plants are not affected. This phenomenon is known as nodricism. Similarly, epiphytic plants represent a widely known case of commensal interactions.

Amensalimo

On the other hand, amensalism also involves a neutral effect in one of the species, and in the other the effect is negative. Some models of this interaction involve the genus Penicillium which secretes certain chemicals that kill nearby bacteria.

The concept can be extrapolated to the plant kingdom. Certain plants secrete a series of substances that inhibit the growth of potential competitors in the perimeter of this.

Indirect effects

The second type of effect that shapes plant communities are indirect. These occur when the impact of one organism on another is mediated or transmitted by a third party. For example A has an effect on B, which has an effect on C.

About seven models of the complex interactions that can occur are proposed, such as key predation, indirect competition, indirect commensalism, among others.

Logically, it is the interactions that have effects - and not neutralisms - that form these complex networks. Furthermore, they are the ones that have an important effect on the community of organisms.

Theories

Few theories have been developed in the field of ecology regarding neutralism. This lack of information is mainly due to the lack of empirical evidence of the existence of relationships in which the fitness of the organisms involved is not affected.

Examples

Although neutralism is not widely accepted by ecologists, some propose that a neutral relationship exists in certain species of bacteria of the Lactobacillus and Streptococcus genera.

The first genus, Lactobacillus, is characterized by being a long or curved bacillus, which responds positively to the Gram stain. Its name is due to its metabolic capacity for the formation of lactic acid, being considered a lactic acid bacteria. It is an important component of the normal bacterial flora of our body.

Streptococcus, on the other hand, is a bacterium in the form of cocci and responds to the Gram stain in a positive way. It is also a lactic acid bacterium and in humans it is the cause of a series of pathologies, such as tonsillitis, meningitis, pneumonia, among others.

Thus, when both bacterial genera are coexisting in the same habitat, it seems that the presence of one does not have a greater effect on the other and vice versa.

Other meanings of the term neutralism

Generally, the concept "neutralism" in the biological sciences is used in the context of modern evolutionary biology. The neutral theory of molecular evolution was proposed by Kimura, and seeks to explain the changes that occur at the DNA level.

According to this theory, the vast majority of mutations that are fixed in DNA by gene drift, since they are selectively neutral. The term "neutralism" or "selectively neutral" is equivalent to saying that they do not pose any advantage or disadvantage to the body.

References

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