Reproductive isolation is the first step in the evolution of the species

With the reproductive isolation of populations of one species begins, it continues and the isolation of the complete ends, the formation of new species of any organisms on our planet. Reproductive isolation is the alpha and omega of the evolution of life on Earth.

Theory of isolation

For panmictic plants and animals (those who reproduce sexually) the concept of "species" unites a set of organisms that are similar in many ways, living in a certain territory and capable of full reproduction. This implies free crossing and the appearance of fertile offspring. Reproductive isolation is the total or partial restriction of free crossing. Also, under the isolation associated with reproduction processes, the reproduction of a sterile hybrid progeny is also understood.

Classification of isolation in biology

Today, different evolutionary scientists offer different systems for classifying species, forms and mechanisms of biological isolation. There are systems that take as a basis the time factor or the completeness of the non-crossing that has arisen. Let us take as the basis the most widespread principle of systematization of isolation knowledge, proposed by the well-known evolutionary biologist FG Dobrzhansky (1900-1975).

All types of insulation differ in the mechanism of their occurrence:

• Geographical isolation of populations;
• Ecological;
• Actually biological.

Let us consider in more detail the forms of reproductive isolation.

Geographical limitation

Geographic reproductive isolation is a restriction in the free crossing of organisms caused by changes in geological nature (the appearance of mountain barriers, changes in the river bed) or the settlement of the species over large areas. In this case, there is a generalization of a group of organisms, the closure of drift and the exchange of genes within an isolated group. The best-known example is the Galapagos finches, different types of which are typical for each island. It was these birds that prompted Charles Darwin to write his work "The Origin of Species by Natural Selection."

Environment and habitat isolation

It is environmental factors that underlie the ecological reproductive isolation of populations of the same species that exist in one area. Such factors may be a mismatch of breeding time or fodder characteristics of individuals. Some scientists believe that this form is not reproductive isolation. This is a partial restriction that does not lead to the impossibility of crossing. And although the opinions of scientists differ, there are examples in nature. On the coast of the Arctic live three kinds of seals. They all descended from a single phylogenetic ancestor. But the seals of Ross eat exclusively cephalopod mollusks, sea leopards are cruel hunters for penguins and other seals, and Witt's seal eats only fish. And they do not cross each other, although they are very similar in appearance.

Reproductive isolation proper

Actually reproductive isolation is the form that is directly tied to the characteristics of the reproductive process. And then they distinguish the doppler and post-copulatory mechanisms that prevent the reproduction of their own kind.

Some scientists call all types of isolation biological or reproductive and include mechanisms of geographic and environmental isolation in the group of pre-indigenous reproductive isolation.

Doppler mechanisms

These are the isolation mechanisms associated with the impossibility of pairing. There are three forms:

1. This is a logical, reproductive isolation associated with the characteristics of sexual behavior. Examples: the ritual marital behavior of birds, the different rhythm of flashing in fireflies, the nature and timbre of mating sounds in frogs, the difference in pheromones (chemical communication substances) of large cats.
2. Mechanical isolation is associated with differences in the structure of the reproductive organs. For example, differences in the structure of the orchid flower lead to the possibility of their pollination by a specific species of hummingbirds. The same is characteristic of different kinds of familiar sage. In animals it is rare. For example, in Drosophila pairing of different species leads to trauma or even death of a partner.
3. Absence of the interaction of gametes (gametes) is called a gemetic isolation. It is proved experimentally in laboratories and zoos. In this case, mating occurs, but the zygote is not impregnated.

Types of post-copulative reproductive isolation

The concept is close to the last kind of docopulyativnoy isolation, but in this case, the embryo is formed. However, it either perishes at the first stages of ontogenesis, or dies before puberty, or hybrid individuals are sterile. The mechanism of death and sterility of hybrids is complex, associated with gene, chromosomal or cytological features. Examples of hybrids of different species are known. Near-hybrids, as an exception, may be capable of reproduction. But then in biology the phenomenon of degeneration of hybrid forms is observed - each subsequent generation of hybrids becomes more and more weakened and gradually degenerates.

Biological significance of reproductive isolation

Not all forms of isolation of populations lead to the formation of new species. But the first step in speciation is always partial or complete isolation of populations or groups of organisms. Over time, when the exchange of gene material closed in an isolated group, accumulates genetic differences from other groups of this species, reproductive isolation becomes more and more significant and complete. With the accumulation of a sufficient number of differences in the genomes, it is said that a new species has formed. In biology, everything is not so simple, sometimes it is rather difficult to single out a group of organisms into a new species. Nevertheless, each catch of deep-sea trawls brings researchers-oceanologists representatives who are not yet known to modern taxonomy.