Every living organism adapts to its environment and looks for the easiest ways for its existence. In the process of evolution, such a species as an animal-parasite was formed. Parasitism is very developed in nature. It arose from the usual symbiosis, when one living organism began to exist at the expense of another. Now, out of a huge number of animal species, more than 6% are parasitic. They can both cause great harm to the host organism, and exist almost unnoticed by him.
How did parasitism come about?
All living organisms enter into various relationships with each other. And not all of them lead to someone's death. In the course of evolution, relationships have been developed that are beneficial to both parties or do them no harm. What phenomena of symbiosis exist in nature?
- Mutualism is a form of relationship in which organisms cannot exist without each other. For example, termites and their flagellate symbiotes that live in their intestines.
- Proto-operation is beneficial for both parties, but not required. An example is the relationship between fish of the wrasse family and moray eels, which they cleanse of parasites.
-Lodging is a type of symbiosis where one species of animal uses another as housing or shelter without harming it. For example, a fish sticking moves with the help of sharks.
- Freeloading is a relationship in which one species feeds on the remains of another's food. For example, annelids or jackals.
- But the most common relationship is competition, when species compete with each other.
- From the previous type of relationship, such relationships appeared when one animal uses another for its own purposes, greatly harming it at the same time. This predation is the eating of one individual by another and actually parasitism. These types of symbiosis are beneficial only to one side, while the other organism suffers in one way or another.
Features of parasitism
Such relationships between different species, in which one organism exists at the expense of another, arose a very long time ago. Over the years of evolution, some animal species have become so adapted to parasitism that they cannot live without the protection of the host. The parasitic animal uses other organisms for food, as places for the development of larvae, and very often as a permanent residence.
There are many types of parasitism, but it is mainly found among lower animals. In addition, the size of organisms is very important. The parasitic animal is mostly small, it uses the body of the host to regulate its relationship with the environment. Due to parasitism, harm to the host organism canbe applied differently, from death to an apparent increase in efficiency. In the course of evolution, more or less stable relationships have been developed between parasites and their carriers, when they minimally affect each other's numbers. It is believed that rarely any individuals are free from parasites. After all, it is almost impossible to protect yourself from this.
What are parasitic animals?
The list of such organisms is quite large, but basically they all belong to several classes. Most often, such animals parasitize on others:
- Protozoa, which are so small that they can be confused with bacteria. These are the causative agents of toxoplasmosis, leishmaniasis, giardiasis, piroplasmosis and other diseases in animals and humans.
- Flatworms and roundworms are the most common parasitic animals. Examples of their names can be found everywhere. After all, they cause various helminthiases and are adapted to life only inside the body of another animal or person. These include roundworms, various nematodes, pinworms, tapeworms and many others.
- A lot of parasites among arthropods. They mainly use the host for food, such as fleas and lice, but some live inside the body.
- Of vertebrates, some cyclostomes, such as lampreys, and bats are parasites. But their symbiosis is more like predation. In addition, nest parasitism is common among some birds. It manifests itself in the fact that, for example, the cuckoo does not build nests, but lays its eggs to other birds.
Types of parasitism
Not all parasitic animals use the host's body throughout their lives. On this basis, their types are distinguished:
1. Temporary parasites are those that go through the entire development cycle in the external environment. They use the host's body only to satisfy hunger. These are insects - parasites of humans and animals: bugs, mosquitoes, horseflies, gadflies and others. Most often, they are blood-sucking, and after eating, they leave the host's body alone.
2. Stationary parasites live in the host organism throughout their lives. But such relationships are periodic and permanent. Periodic parasitism is when the organism uses the host only in one stage of its development. For example, gadflies parasitize only in the form of a larva, and helminths - in most cases - in the mature stage. A parasitic animal that spends its entire life in the host's body is called permanent. These are lice, scabies mites and some others.
Types of parasites by place of life
Different species can parasitize both outside the host organism, on his skin and coat, and inside his body. According to these features, two types are distinguished:
1. The most unpleasant for the owner are external parasitic animals. Their list is very impressive, and most of them are familiar to all warm-blooded animals, including humans. Most of them are carriers of dangerous infectious diseases. These are various ticks, fleas, lice, mosquitoes and others. They are also divided intoseveral groups. Some of them only temporarily sit on the host to take food, such as mosquitoes. Others constantly live on the skin - lice, gnaw through passages in the upper layer of the epidermis - scabies or sand fleas, or choose various body cavities as their residence: nose, ear, eye or mouth. These are, for example, gadfly larvae.
2. There are also a lot of internal parasites that permanently or temporarily reside in various organs of another animal. But they are not so noticeable, although they can cause irreparable harm to the host's body. They can migrate inside the body and settle not only in the intestines, but also in muscles, blood cells and even in the brain. In this way, various protozoa and worms parasitize.
What are the hosts?
Most often there are two groups into which organisms used by parasites are divided. These are mandatory and optional. Mandatory hosts are those that are habitual for parasites, and it is their organisms that are the most favorable environment for their life. Facultative species are used by parasites for lack of a better one. In addition, most parasitic organisms go through several stages in their development. And often, for each stage of its development, it needs a different host. For example, the malarial Plasmodium uses a female mosquito and a human body. Biologists have found that the intermediate host in which the larva develops is eaten by predators, and thus the parasite continues to develop. Larvae can get into a permanent host through water.or the ground.
Evolution of parasites
In the process of adapting to life inside another organism, parasitic species have acquired some features. In most of them, the organs of movement atrophied, and various suckers, hooks for holding on the host's body, developed. In blood-sucking species, special enzymes are secreted that thin the blood of the victim and increase its flow to the skin. Some parasites have lost their digestive functions and can, for example, absorb food from the entire surface of the body, like some helminths. But those organisms that live inside the host had to develop defense mechanisms. For example, helminths produce anti-enzymes in order not to be digested by gastric juice. The organism of the parasite is simplified, but the function of reproduction in most cases increases. And their larvae have special defense mechanisms that help them survive in an unfavorable environment.
What harm do parasites do to the host?
Symbiosis does not always lead to the death of one organism. In most cases, it is to the advantage of the parasite that its host survives. But poisoning with metabolic products or destruction of tissues most often leads to illness and death of the individual. Insects - parasites of animals cause the least harm. But the constant itching from the presence of ticks or lice, damage to the coat or feathers in birds leads to a decrease in efficiency and greater availability of the individual for predators.
For humans, parasites of domestic animals are especially dangerous,that can infect him. These include, first of all, various helminths that cause damage to internal organs, poisoning with metabolic products of their vital activity and deterioration of well-being.
Plant parasites
Some species parasitize not only on living organisms, but also on plants. They suck the nutrients out of them. Most often this leads to the death of the plant. These types of parasites include many nematodes living in the roots, as well as a large number of insects: aphids, mites, molluscs, butterflies and many others. They can parasitize leaves and stems, attaching to them or moving from place to place.
