Each living organism adapts to the surrounding conditions and searches for the easiest ways for its existence. In the process of evolution, a species such as an animal parasite was formed. Parasitism is very developed in nature. It arose from ordinary symbiosis, when one living organism began to exist at the expense of another. Now of the huge number of animal species, more than 6% are parasitic. They can both cause great harm to the host’s body and exist almost imperceptibly for 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 useful to both parties or do no harm to them. 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 symbiotes are flagellates living in their intestines.
- Protocooperation is beneficial for both parties, but not required. An example is the relationship of fish of the Gubanov family and moray eels, which they clear of parasites.
- Lodging is a kind of symbiosis when one species of animal uses another as a shelter or shelter without harming it. For example, the fish stuck around using sharks.
- Hijacking is a relationship in which one species eats the remnants of the food of another. 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 appeared when one animal uses the other for its own purposes, greatly harming it at the same time. This predation is the eating of one individual by another and parasitism itself. These types of symbiosis are beneficial only to one side, and the other body suffers to one degree 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 species of animals have adapted to parasitism so much that they cannot live without host protection. The animal parasite uses other organisms to obtain food, as places for the development of larvae, and very often as a permanent place of residence.
There are many types of parasitism, but mainly it is found among lower animals. In addition, the size of organisms is very important. The parasite animal is mostly small; it uses the host's body to regulate its relations with the environment. Due to parasitism, the host organism can be damaged in a variety of ways, from death to an apparent increase in performance. In the course of evolution, more or less stable relations between parasites and their carriers have developed, when they have a minimal effect on each other's numbers. It is believed that rarely some 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 that are so small that they can be confused with bacteria.” These are the causative agents of toxoplasmosis, leishmaniasis, giardiasis, pyroplasmosis and other diseases in animals and humans.
- Flat and round worms are the most common animal parasites. 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 nutrition, for example, fleas and lice, but some live inside the body.
- Of the 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 with other birds.
Types of Parasitism
Not all parasitic animals use the body of the host 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 their 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 organism alone.
2. Stationary parasites live in the host's body throughout their entire lives. But such relationships are periodic and permanent. Periodic parasitism is when the body 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 a mature stage. An animal parasite that spends its entire life in the host is called permanent. These are lice, scabies mites and some others.
Types of parasites at the place of life
Various species can parasitize both outside the host’s body, on its skin and coat, and inside its body. According to these signs, two types are distinguished:
1. The most unpleasant for the owner are external animal parasites. Their list is very impressive, and the majority are familiar with 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 into several groups. Some of them only temporarily sit on the host to take food, for example, mosquitoes. Others constantly live on the skin - lice, gnawing passages in the upper layer of the epidermis - scabies itch or sand flea, or they choose different body cavities as a place of residence: nose, ear, eye or mouth. This, for example, gadfly larvae.
2. There are also many 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. They can migrate inside the body and settle not only in the intestines, but also in the muscles, blood cells, and even in the brain. Thus various protozoa and worms parasitize.
What are the owners?
Most often, two groups are distinguished into which the organisms used by parasites are divided. These are required and optional. Mandatory hosts are those that are familiar to parasites, and it is their organisms that are the most favorable environment for their lives. Optional species are used by parasites for want of a better one. In addition, most parasitic organisms undergo several stages in their development. And often for each stage of his development he needs a different host. For example, a malarial plasmodium uses a female mosquito and the 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 enter the permanent host through water or land.
Parasite evolution
In the process of adaptation to life inside another organism, parasitic species acquired some features. Most of them atrophied the organs of movement, and developed various suckers, hooks for holding on the body of the owner. In blood-sucking species, special enzymes are secreted that dilute the victim’s blood and increase its flow to the skin. Some parasites have lost their digestive functions and can, for example, absorb food throughout the body, like some helminths. But those organisms that live inside the host had to develop protective mechanisms. For example, helminths produce antienzymes so as not to be digested by gastric juice. The body of the parasite is simplified, but the reproduction function in most cases increases. And their larvae have special protective mechanisms that help to survive in an unfavorable environment.
What harm do parasites cause to the host?
Not always symbiosis leads to the death of one organism. In most cases, it is beneficial for the parasite to survive. But poisoning by metabolic products or tissue destruction most often leads to illness and death of an individual. Least of all harm is caused by insects - animal parasites. But the constant itching from the presence of ticks or lice, damage to the coat or feathers of birds leads to reduced performance and greater accessibility of the individual for predators.
Parasites of domestic animals that can infect him are especially dangerous for humans. These include, first of all, various helminths that cause damage to internal organs, poisoning by metabolic products of one’s vital activity and deterioration of well-being.
Plant Parasites
Some species parasitize not only on living organisms, but also on plants. They suck out nutrients from 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, ticks, mollusks, butterflies and many others. They can parasitize on leaves and stems, attaching to them or moving from place to place.