Isolation mechanisms in biology. Types of insulating mechanisms, examples
No one will deny that the environment around usreality is harmonious and perfect. It does not matter what or in whom a person believes, but around him he sees not only beauty and diversity, but also a harmonious order, in which there is no place for chaos. Especially clearly, a clear expediency is manifested in the world of living beings. All weak, ugly, incapable of reproducing healthy offspring is rejected by the action of evolution factors, above all, by natural selection. Not the least role in it is played by a biological process, such as reproductive isolation.
This, as well as other forms of protective mechanisms that protect the gene pool of plant, animal and human communities, we will consider in this paper.
The transfer of hereditary traits is the main property of living matter
Reproduction is the most important process, thanks towhich is the very existence of the phenomenon of life on Earth. Regardless of the level of its organization, starting from the simplest and ending with mammals, fertilization (in plants - pollination), leading to the emergence of viable, fertile offspring, occurs only between individuals belonging to a population of the same biological species. Obviously, there are natural isolation mechanisms that control copulation or pollination.
Of course, the possibility of casesinterspecific crossing. They occur both in natural conditions and are carried out artificially - by man, but always lead to the appearance of either offspring with weakened viability, or sterile hybrids. Suffice it to recall the fruitless mules - descendants obtained from crossing the donkey and the mare. As we see, certain forces act here, which can be considered as certain types of isolating mechanisms. Let us define them in more detail.
Classification of processes leading to the stability of the gene pool of populations
In evolutionary teaching, which is a productjoint scientific work of such natural scientists as Charles Darwin, A.N. Severtsov, G. Spencer, consider the following, widespread phenomena contributing to the stability of the existence of biological species: geographic, reproductive and ecological isolation. Section biology - population genetics, is engaged in studying the changes occurring in the gene pool of communities of living organisms. They are the consequence of the action of such factors as the waves of life and the drift of genes.
The above branch of biology establishes the role ofprotective factors aimed at preserving the conservatism of karyotypes of individuals of the population and preventing interpopulation crosses. Next, we will find out what isolation mechanisms are called ecological, and what is their significance in maintaining the unchanged composition of genes in the population.
The role of environmental conditions in the conservation of the gene pool of communities of living organisms
As a result of phylogenesis - historical developmentspecies, its individuals, form populations inhabiting the boundaries of a certain territory, called the area. Vegetable and animal organisms interact with environmental factors, as well as with communities of other species that live in a given territory, that is, they occupy a certain ecological niche. To reduce the intensity of competition between populations of the same species, there are certain isolation mechanisms that ensure, for example, a discrepancy between the requirements of both groups for the type of food. So, the beetle pea beetle forms two communities of insects: one feeds on seeds of peas, another - beans.
During the reproductive period, due to the fact that fodder crops grow in different zones, the organisms of the two populations do not interbreed with one another.
The timing of reproduction and their significance in ensuring genetic stability of the population
To factors that significantly hamper, or evencompletely suppressing pollination or copulation between organisms of one systematic category, it is possible to include isolating mechanisms that control the terms of reproduction of individuals. For example, the flowering of meadow grassland growing in estuaries of rivers is correlated with the time of spring flood termination. Plants that live directly on the shore, and during floods for a long time under water, bloom later than those individuals that were under the influence of high water short-term, or, in general, not flooded. For obvious reasons, panmixia (cross pollination) between plants living in different places of the meadow is absent, as the ripening of pollen takes place at different times. As a result, several populations of meadow grasshopper are formed, differing in terms of reproduction time.
Evolutionary role of isolation
Population genetics established the fact thatthe impossibility of the process of gene exchange between organisms of different races or communities leads to the fact that completely different types of mutations occur in the genotypes of individuals, and the frequency of occurrence of both dominant and recessive alleles varies. This leads to the fact that the gene pools of populations increasingly differ among themselves. This discrepancy will concern, first of all, the forms of adaptation to the abiotic factors of the environment. What does it depend on?
Complex action of various types of insulation
It is based on interrelated onesecological and reproductive isolation mechanisms. Biology, in particular, its division - the theory of evolution, reveals their influence on the manifestation of such a global process as divergence, that is, the divergence of signs and properties of organisms. It underlies microevolution - a process leading to the formation of subspecies first, and then, and new biological species in nature.
How does geographical isolation occur?
Both in botany and in zoology, scientists payserious attention is paid to the factor, which reduces to almost zero the probability of free crossing between individuals of the same species. It received the name of geographical isolation. It turned out that a sharp change in the terrain is necessarily accompanied by the appearance of obstacles that lead to the emergence of cardinal differences in organisms.
They relate, first of all, to maturationgametes, copulation time or pollination. All these factors can be combined in one term - reproductive isolation. What are the consequences for the existence of the population?
Variation in characteristics
Scientists have established that populations of organisms,having initially similar genomes, with the passage of time acquire ever greater divergent features due to the disappearance of both a single food base and the possibility of free crossing. Irresistible physical barriers in the form of continental faults, uplift of mountain ranges, floods of rivers isolate communities of individuals from each other. This is how the living nature develops. The examples below illustrate geographical isolation as an important mechanism for speciation. Thus, the group of marsupial mammals of Australia, after its separation from the ancient continent of Gondwana, have significant anatomical and physiological differences from the modern European species of animals that arose after the Great Glaciation.
Charles Darwin on the mechanisms of speciation
The world-famous creator of the theory of naturalselection, the English naturalist Charles Darwin, determined the driving forces of evolution, leading to the emergence of new classes, orders and families of living organisms. Also in his writings, the scientist described geographic and ecological isolating mechanisms. Examples of their manifestation, he drew from observations conducted during his famous round-the-world trip. Darwin saw and sketched the various species of finches that inhabit the Galapagos Islands. Birds had cardinal differences in the shape of the beak, the size of the trunk, and fed various foods.
When crossing each other completelylost the ability to form fertile offspring. As the researcher believed, the large distances between the islands and the differences in their flora and fauna led to the formation of several subspecies, then turned into independent species. We have considered one more direction of evolution, leading to the formation of new biological species, along which the entire existing living nature is advancing. The examples discussed above prove the important role of spatial mechanisms preventing the probability of crosses between the organisms of different populations, which ultimately leads to the appearance of new systematic units.