Parasitization is one of the oldest forms of coexistence of organisms. From the Greek language, the word "parasite" can be translated as "freeloader". Indeed, the essence of parasitism is that two genetically heterogeneous organisms coexist for a sufficiently long period, while one of the organisms serves not only as a habitat for the other, but also as a source of food. Such an interesting, from a biological point of view, phenomenon as obligate parasitism will be discussed in this article.
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 becomes dependent on the state. For such people, special boarding houses were built, which were called parasitaria. Well, the residents of these pensions were called parasites. That is, initially a parasite is one that is able to exist solely at the expense of others.
Parasitic organisms
Now parasites are creatures whose existence is impossible without other individuals belonging to a different biological species. The parasite can completely lose the ability to live independently (these are the so-called obligate parasites), or switch to a parasitic lifestyle only at certain stages of its development.
It is important to note that the parasite benefits from coexisting with the host, while harming the latter. In this case, the harm can vary within a fairly wide range: from damage to the tissues of various organs or exhaustion to a change in the behavior of the host. That is why, in case of infection, a cure for parasites is necessary: otherwise, irreparable damage may be caused to the body. As an example, there are numerous drugs or medicines to 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 both on the surface of the host's body and in the cavities of its internal organs or even in cells.
A rather characteristic feature of parasitic organisms is the reduction of some organs in them, in which, due to the mode of existence, there is no need. For example, parasites often lack a digestive system, sensory organs, or limbs. Interestingly, in the course of evolutionary development, parasites never “return” the lost organ systems:only further simplification of the organism is possible. As an example of such a simplification, we can cite viruses, which, as scientists believe, have turned from single-celled microorganisms into a DNA or RNA molecule “packed” in a protein shell. Viruses are so primitive that some researchers don't even consider them living organisms.
Evolution of parasitism
Scientists believe that parasitism arose at that moment in the development of the living world, when the first biogeocenoses appeared on earth. Due to the strengthening of bonds 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 body of the other. 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 defense mechanisms of the host organism. For example, bacteria thicken their cell walls, special structures develop on the limbs of ticks that prevent combing, etc.
Parasites: main varieties
There are three main varieties of parasitic organisms:
- Facultative parasites. They spend part of their lives as free individuals, and only some stages of development, as a rule, reproduction, are associated with a parasitic way of life. An example is some types of intestinal bacteria.
-obligate parasites. All stages of the life cycle of such parasites are associated with the host organism. Such a parasite cannot exist in the external environment. Obligate 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 fungi, which can cause the development of subcutaneous mycoses in humans.
There is another variety of parasitic organisms - the so-called superparasites. Such organisms use other parasites as hosts. Superparasitism is a fairly common phenomenon in nature, which is of great ecological importance: such organisms regulate the population of parasitic organisms.
Bad news in a protein package
Obligate parasites are viruses - microorganisms that are not capable of reproducing outside the cell. Biologists believe that viruses evolved from more complex microorganisms that became parasitic and lost most of their genes and cellular structures. Viruses do not even have the ability to self-metabolize: they use the metabolic processes in the infected cell to obtain energy.
According to Nobel Prize winner P. Medawar, a virus is “bad news wrapped in protein”. This is indeed true: the structure of viruses has been simplified to the limit. Viruses are a DNA or RNA molecule protected bya protein coat called the capsid. Once in the cell, the virus genes begin to actively reprogram the work of biochemical systems, forcing 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: there is not a single biological species in the world that could not be susceptible to viral infections. Viruses can parasitize not only in animal and plant cells, but also in unicellular microorganisms. Surprisingly, these are the only obligate parasites that are not only not capable of independent free existence, but also exhibit the properties of living matter only when they enter the host's body.
Despite the damage the virus can do to the body, a cure for parasites that infect cells may not be effective. Unfortunately, viruses, obligate intracellular parasites of the highest level, multiply quite quickly. Their evolution overtakes the pharmacological industry. Therefore, these obligate intracellular parasites, having a simple, if not primitive structure, now and then defeat the king of nature - man …
Today, scientists have come to the conclusion that parasitic organisms are one of the main engines of evolution. You should not think that these creatures bring only harm: obligate parasites, examples of which are given in this article, are extremely interesting creatures for research, without which developmentliving world seems impossible.
