With the reproductive isolation of populations of one speciesbegins, 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.
For panmictic plants and animals (those whoreproduces 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.
Today, different scientists - evolutionists offervarious systems of classification of 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's take as a 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:
Let us consider in more detail the forms of reproductive isolation.
Geographic reproductive isolation isrestrictions 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 most famous 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."
It is environmental factors that underlie environmentalReproductive isolation of populations of the same species existing on the same territory. Such factors may be a mismatch between the time of reproduction or the feeding 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 itself is thatform, which 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 geographical and ecological isolation in the group of pre-indigenous reproductive isolation.
These are the isolation mechanisms associated with the impossibility of pairing. There are three forms:
The concept is close to the last kind of dokopulyativnoyisolation, 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.
Not all forms of isolation of populations lead tothe 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 quite difficult to distinguish 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.