Obligatory parasites: types, characteristics, examples

Parasitizing is one of the oldest forms of coexistence of organisms. From the Greek language, the word "parasite" can be translated as a "parasite". Indeed, the essence of parasitism is that two genetically dissimilar organisms coexist for a sufficiently long period, while one of the organisms serves not only as the environment for the other, but also as a source of food. About such an interesting, from a biological point of view, phenomenon, as an obligate parasitism, this article will be discussed.

Where did the term "parasitism" come from?

In ancient Greece, there was a law: when a statesman becomes too old to fulfill his immediate duties, he goes over to state support. For such people were built special boarding houses, which were called parasitarians. Well, the residents of these boarding houses were called parasites. That is, initially a parasite is one that can exist exclusively at someone else's expense.

Parasitic organisms

Now, parasites are called creatures whose existence is impossible without other individuals belonging to another biological species. The parasite can completely lose its ability to live independently (this is the so-called obligate parasites), or to pass to the parasitic way of life only at certain stages of its development.

It is important to note that the parasite benefits from coexistence with the host, while doing the latter harm. In this case, the harm can vary in a fairly wide range: from damage to tissues of various organs or exhaustion to a change in the behavior of the host. That is why, in case of infection, you need a medicine for parasites: otherwise the body can be irreparably damaged. As an example, there are numerous drugs or medicines that can get rid of worms.

Features of parasitic organisms

Unlike predation, parasitism involves the adaptation of the parasite to the characteristics of the host organism. Parasites can live on both the surface of the host's body, and in the cavities of its internal organs or even in cells.

Quite a characteristic feature of parasitic organisms is the reduction in them of certain organs, in which, by virtue of the mode of existence, there is no need. For example, often parasites lack digestive system, sense organs or limbs. It is interesting that parasites in the course of evolutionary development never "return" lost organ systems: only further simplification of the organism is possible. An example of this simplification is viruses, which scientists believe to have turned from single-celled microorganisms into a DNA or RNA molecule "packed" into a protein envelope. Viruses are so primitive that some researchers do not even consider them to be living organisms.

Evolution of parasitism

Scientists believe that parasitism arose at the time of the development of the living world, when the first biogeocenoses appeared on the earth. Due to the strengthening of connections between organisms, various forms of symbiotic relationships arose, representing the coexistence of individuals belonging to different biological species. At the same time, one of the species gradually began to adapt to the organism of another. The specialization became so narrow that the former symbiont could no longer exist without the host organism and became a parasite. Most parasites adapt to the protective mechanisms of the host organism. For example, in bacteria the cell walls thicken, special structures that prevent combing out develop on the extremities of the mites, and so on.

Parasites: basic varieties

There are three main types of parasitic organisms:

- Optional parasites. They spend part of their lives as free individuals, and only a few stages of development are associated with the parasitic way of life, as a rule, reproduction. As an example, some types of intestinal bacteria can be cited.

- Obligatory parasites. All stages of the life cycle of such parasites are associated with the host organism. In the external environment such a parasite can not exist. Obligatory parasites are all viruses, rickettsia and chlamydia.

- Random parasites. This is a relatively small group of organisms that pass to parasitism by accident. An example is the fungi, which can lead to the development of subcutaneous mycoses in man.

There is another type of parasitic organism - the so-called superparasites. Such organisms use other parasites as hosts. Superparasitism - a fairly widespread phenomenon in nature, which has a huge ecological significance: such organisms regulate the population of parasitic organisms.

"Bad news in the packaging of protein"

Obligate parasites are viruses - microorganisms that are not capable of reproduction outside the cell. Biologists believe that the viruses originated from more complex microorganisms that have passed to a parasitic lifestyle and have lost most of their genes and cellular structures. Viruses do not even have the capacity for independent metabolism: to obtain energy, they use metabolic processes in the infected cell.

According to the definition of the Nobel Prize winner P. Medavar, the virus is "bad news in the package of protein." It really is so: the structure of the viruses has become simpler to the limit. Viruses are a DNA or RNA molecule protected by a protein coat called the capsid. Getting into the cell, the virus genes begin to actively reprogram the work of biochemical systems, causing them to reproduce the proteins necessary for the reproduction of the virus .

Viruses as absolute parasites

Viruses can be called a kind of "kings" of parasites: in the world there is no single species that could not be affected by viral infections. Viruses can parasitize not only in cells of animals and plants, but also in unicellular microorganisms. Surprisingly, these are the only obligate parasites that are not only incapable of independent free existence, but also exhibit the properties of living matter only when they enter the host's body.

Despite the harm that the virus can inflict on the body, the cure for parasites that damage cells may not be effective. Unfortunately, viruses, obligate intracellular parasites of the highest level multiply rapidly enough. Their evolution outstrips the pharmacological industry. Therefore, these obligate intracellular parasites that have a simple, if not primitive structure, now and then defeat the nature king - man ...

Nowadays, scientists have come to the conclusion that parasitic organisms are one of the main engines of evolution. It is not worth thinking that these creatures are extremely harmful: obligate parasites, the examples of which are given in this article, are extremely interesting for study by beings without which the development of the living world seems impossible.