Moose species criteria. Morphological criterion of the species. The geographical criterion of a species is that

View (lat. species) is a taxonomic, systematic unit, a group of individuals with common morphophysiological, biochemical and behavioral characteristics, capable of interbreeding, producing fertile offspring in a number of generations, regularly distributed within a certain range and similarly changing under the influence of environmental factors. A species is a really existing genetically indivisible unit of the living world, the main structural unit in the system of organisms, a qualitative stage in the evolution of life.

For a long time it was believed that any species is a closed genetic system, that is, there is no exchange of genes between the gene pools of two species. This statement is true for most species, but there are exceptions to it. So, for example, lions and tigers can have common offspring (ligers and tigers), the females of which are fertile - they can give birth both from tigers and lions. Many other species are also interbred in captivity, which do not naturally interbreed due to geographic or reproductive isolation. Crossing (hybridization) between different species can also occur in natural conditions, especially in the case of anthropogenic disturbances of the habitat that violate the ecological mechanisms of isolation. Especially often plants hybridize in nature. A noticeable percentage of higher plant species is of hybrid origin - they were formed during hybridization as a result of partial or complete merging of parental species.

Basic view criteria

1. Morphological criterion of the species. It is based on the existence of morphological features characteristic of one species, but absent in other species.

For example: in an ordinary viper, the nostril is located in the center of the nasal shield, and in all other vipers (nosed, Asia Minor, steppe, Caucasian, viper) the nostril is shifted to the edge of the nasal shield.
At the same time, there are significant individual morphological differences within species. For example, the common viper is represented by a variety of color forms (black, gray, bluish, greenish, reddish and other shades). These features cannot be used to distinguish species.

2. geographical criterion. It is based on the fact that each species occupies a certain territory (or water area) - a geographical area. For example, in Europe, some species of the malarial mosquito (genus Anopheles) inhabit the Mediterranean, others - the mountains of Europe, Northern Europe, Southern Europe.

However, the geographical criterion is not always applicable. The ranges of different species may overlap, and then one species smoothly passes into another. In this case, a chain of vicarious species (superspecies, or series) is formed, the boundaries between which can often be established only through special studies (for example, the herring gull, the black-backed gull, the western gull, the California gull).

3. ecological criterion. Based on the fact that two species cannot occupy the same ecological niche. Therefore, each species is characterized by its own relationship with the environment.

However, within the same species, different individuals can occupy different ecological niches. Groups of such individuals are called ecotypes. For example, one ecotype of Scotch pine inhabits swamps (marsh pine), another - sand dunes, the third - leveled areas of forest terraces.

A set of ecotypes that form a single genetic system (for example, capable of interbreeding with each other to form full-fledged offspring) is often called an ecospecies.

4. Molecular genetic criterion. Based on the degree of similarity and difference in nucleotide sequences in nucleic acids. As a rule, "non-coding" DNA sequences (molecular genetic markers) are used to assess the degree of similarity or difference. However, DNA polymorphism exists within the same species, and different species can be characterized by similar sequences.

5. Physiological and biochemical criterion. It is based on the fact that different species can differ in the amino acid composition of proteins. At the same time, protein polymorphism exists within a species (for example, intraspecific variability of many enzymes), and different species can have similar proteins.

6. Cytogenetic (karyotypic) criterion. It is based on the fact that each species is characterized by a certain karyotype - the number and shape of metaphase chromosomes. For example, all hard wheats have 28 chromosomes in the diploid set, and all soft wheats have 42 chromosomes. However, different species can have very similar karyotypes: for example, most species of the cat family have 2n=38. At the same time, chromosomal polymorphism can be observed within the same species. For example, in elks of Eurasian subspecies 2n=68, and in elks of North American species 2n=70 (in the karyotype of North American elks there are 2 less metacentrics and 4 more acrocentrics). Some species have chromosome races, for example, in a black rat - 42 chromosome (Asia, Mauritius), 40 chromosome (Ceylon) and 38 chromosome (Oceania).

7. reproductive criterion. It is based on the fact that individuals of the same species can interbreed with each other with the formation of fertile offspring similar to their parents, and individuals of different species living together do not interbreed with each other, or their offspring are sterile.

However, it is known that interspecific hybridization is often common in nature: in many plants (for example, willows), a number of fish species, amphibians, birds and mammals (for example, a wolf and a dog). At the same time, within the same species, there may be groupings that are reproductively isolated from each other.

8. ethological criterion. Associated with interspecies differences in behavior in animals. In birds, song analysis is widely used for species recognition. By the nature of the sounds produced, different types of insects differ. Different types of North American fireflies differ in the frequency and color of light flashes.

9. Historical (evolutionary) criterion. Based on the study of the history of a group of closely related species. This criterion is complex in nature, since it includes a comparative analysis of modern species ranges (geographical criterion), a comparative analysis of genomes (molecular genetic criterion), a comparative analysis of cytogenomes (cytogenetic criterion), and others.

None of the considered species criteria is the main or the most important one. For a clear separation of species, they must be carefully studied according to all criteria.

Due to unequal environmental conditions, individuals of the same species within the range break up into smaller units - populations. In reality, a species exists precisely in the form of populations.

Species are monotypic - with a weakly differentiated internal structure, they are characteristic of endemics. Polytypic species are characterized by a complex intraspecific structure.

Within species, subspecies can be distinguished - geographically or ecologically isolated parts of a species, individuals of which, under the influence of environmental factors in the process of evolution, have acquired stable morphophysiological features that distinguish them from other parts of this species. In nature, individuals of different subspecies of the same species can freely interbreed and produce fertile offspring.

species name

The scientific name of a species is binomial, that is, it consists of two words: the name of the genus to which the given species belongs, and the second word, called the species epithet in botany, and the species name in zoology. The first word is a singular noun; the second is either an adjective in the nominative case, agreed in gender (masculine, feminine or neuter) with a generic name, or a noun in the genitive case. The first word is capitalized, the second is lowercase.

• Petasites fragrans- the scientific name of a species of flowering plants from the genus Butterbur ( Petasites) (the Russian name of the species is Fragrant Butterbur). The adjective is used as a specific epithet Fragrans("fragrant").
• Petasites fominii- the scientific name of another species from the same genus (Russian name - Fomin Butterbur). The Latinized surname (in the genitive case) of the botanist Alexander Vasilyevich Fomin (1869-1935), a researcher of the flora of the Caucasus, was used as a specific epithet.

Sometimes entries are also used to designate indeterminate taxa at species rank:

• Petasites sp.- the entry indicates that the taxon at the rank of species, belonging to the genus, is meant Petasites.
• Petasites spp.- entry means that all taxa in the rank of species included in the genus are meant Petasites(or all other taxa in the rank of species included in the genus Petasites, but not included in any given list of such taxa).

The qualitative stage of the process of evolution is the species. A species is a collection of individuals that are similar in morphological and physiological characteristics, are able to interbreed, produce fertile offspring and form a system of populations that form a common area.

Each type of living organisms can be described on the basis of a set of characteristic features, properties, which are called signs. Species features that distinguish one species from another are called species criteria. There are six general species criteria most commonly used: morphological, physiological, geographical, ecological, genetic, and biochemical.

The morphological criterion involves the description of the external (morphological) features of individuals that are part of a particular species. In appearance, size and color of plumage, for example, it is easy to distinguish a large spotted woodpecker from a green one, a small spotted woodpecker from a yellow one, a great tit from a crested, long-tailed, blue and from a tit. By the appearance of the shoots and inflorescences, the size and arrangement of the leaves, the types of clover are easily distinguished: meadow, creeping, lupine, mountain.

The morphological criterion is the most convenient and is therefore widely used in taxonomy. However, this criterion is not sufficient to distinguish between species that have significant morphological similarities. To date, facts have been accumulated that testify to the existence of twin species that do not have noticeable morphological differences, but do not interbreed in nature due to the presence of different chromosome sets. So, under the name “black rat”, two twin species are distinguished: rats with 38 chromosomes in the karyotype and living throughout Europe, Africa, America, Australia, New Zealand, Asia west of India, and rats with 42 chromosomes, distribution which is associated with the Mongoloid settled civilizations inhabiting Asia east of Burma. It has also been established that under the name "malarial mosquito" there are 15 outwardly indistinguishable species.

The physiological criterion lies in the similarity of life processes, primarily in the possibility of crossing between individuals of the same species with the formation of fertile offspring. There is a physiological isolation between different species. For example, in many species of Drosophila, the sperm of a foreign species causes an immunological reaction in the female genital tract, which leads to the death of spermatozoa. At the same time, interbreeding is possible between certain types of living organisms; in this case, fertile hybrids (finches, canaries, crows, hares, poplars, willows, etc.) can be formed.

The geographical criterion (geographical certainty of a species) is based on the fact that each species occupies a certain territory or water area. In other words, each species is characterized by a certain geographical range. Many species occupy different ranges. But a huge number of species have coinciding (overlapping) or overlapping ranges. In addition, there are species that do not have clear distribution boundaries, as well as cosmopolitan species that live on vast expanses of land or ocean. Cosmopolitans are some inhabitants of inland waters - rivers and freshwater lakes (species of pondweed, duckweed, reed). An extensive set of cosmopolitans is found among weeds and garbage plants, synanthropic animals (species that live near a person or his dwelling) - a bed bug, a red cockroach, a house fly, as well as a medicinal dandelion, a field yaruka, a shepherd's purse, etc.

There are also species that have a broken range. So, for example, linden grows in Europe, is found in the Kuznetsk Alatau and the Krasnoyarsk Territory. The blue magpie has two parts of its range - Western European and East Siberian. Due to these circumstances, the geographical criterion, like others, is not absolute.

The ecological criterion is based on the fact that each species can exist only under certain conditions, performing the corresponding function in a certain biogeocenosis. In other words, each species occupies a specific ecological niche. For example, the caustic buttercup grows in floodplain meadows, the creeping buttercup grows along the banks of rivers and ditches, the burning buttercup grows in wetlands. There are, however, species that do not have a strict ecological confinement. First, these are synanthropic species. Secondly, these are species that are under human care: indoor and cultivated plants, pets.

The genetic (cytomorphological) criterion is based on the difference between species by karyotypes, i.e. number, shape and size of chromosomes. The vast majority of species are characterized by a strictly defined karyotype. However, this criterion is not universal. First, in many different species, the number of chromosomes is the same and their shape is similar. So, many species from the legume family have 22 chromosomes (2n=22). Secondly, individuals with different numbers of chromosomes can occur within the same species, which is the result of genomic mutations. For example, goat willow has a diploid (38) and tetraploid (76) chromosome number. In silver carp, there are populations with a set of chromosomes 100, 150,200, while their normal number is 50. specific type.

The biochemical criterion makes it possible to distinguish species according to biochemical parameters (composition and structure of certain proteins, nucleic acids and other substances). It is known that the synthesis of certain macromolecular substances is inherent only in certain groups of species. For example, according to the ability to form and accumulate alkaloids, plant species differ within the families of Solanaceae, Compositae, Liliaceae, and Orchids. Or, for example, for two species of butterflies from the genus Amata, the diagnostic feature is the presence of two enzymes - phosphoglucomutase and esterase-5. However, this criterion is not widely used - it is laborious and far from universal. There is a significant intraspecific variability in almost all biochemical parameters up to the sequence of amino acids in protein molecules and nucleotides in individual DNA regions.

Thus, none of the criteria alone can serve to determine the species. It is possible to characterize a species only by their totality.

The set of properties and common features inherent in one species is called the species criterion. Typically, six to ten species definition criteria are used.

Systematization

A species is a systematic or taxonomic unit that has a common characteristic and unites a group of living organisms on its basis. To isolate a biological group into one species, one should take into account a number of features associated not only with distinctive external features, but also with living conditions, behavior, distribution, etc.

The concept of "species" was used to group outwardly similar animals into groups. By the end of the 17th century, a lot of information about species diversity had accumulated, and the classification system required revision.

Carl Linnaeus in the 18th century united species into genera, and genera into orders and classes. He proposed a binary nomenclature of designations, which helped to significantly shorten the names of species. According to Linnaeus, the names began to consist of two words - the names of the genus and the species.

Rice. 1. Carl Linnaeus.

Linnaeus was able to systematize species diversity, but he himself erroneously distributed animals by species, relying mainly on external data. For example, he attributed the male and female ducks to different species. Nevertheless, Linnaeus made a huge contribution to the study of species diversity:

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• classified plants by gender (dioecious, monoecious, polyecious);
• identified six classes in the animal kingdom;
• attributed man to the class of primates;
• described about 6000 animals;
• He was the first to conduct experiments on plant hybridization.

Later, the biological concept of the species appeared, confirming that the classification by species is natural, genetically determined, and not artificial, created by people for the convenience of systematization. In fact, the species is an indivisible unit of the biosphere.

Despite the possibilities of modern science, many species have not yet been described. As of 2011, about 1.7 million species have been described. At the same time, there are 8.7 million species of plants and animals in the world.

Criteria

According to the criteria, it is possible to determine whether individuals belong to the same or to different species. First of all, the morphological criterion of the species is distinguished, i.e. representatives of different species should differ in external and internal structure.

However, often this criterion is not enough to distinguish a group of living organisms into a separate species. Individuals may differ in behavior, lifestyle, genetics, so it is important to take into account a set of criteria and not draw conclusions based on one trait.

Rice. 2. Morphological similarity of barbel species.

The table “Criteria of species” describes the most important criteria by which a species can be recognized.

None of the criteria is absolute and has exceptions to the rules:

• outwardly dissimilar species have the same set of chromosomes (cabbage and radish - 18 each), while mutations can be observed within the species and populations with a different set of chromosomes can be found;
• black rats (twin species) are morphologically identical, but genetically they are not, and, therefore, cannot produce offspring;
• in some cases, individuals of different species interbreed (lions and tigers);
• ranges often intersect or are broken (the Western European and East Siberian range of the magpie).

Hybridization is one of the levers of evolution. However, for successful crossing and obtaining fertile offspring, many criteria must match - genetics, biochemistry, physiology. Otherwise, the offspring will not be viable.

Rice. 3. Liger - a hybrid of a lion and a tigress.

What have we learned?

From the 11th grade biology lesson, we learned about the concept of a species and the criteria for its definition, considered nine main criteria with examples given. The criteria should be considered together. Only if several criteria are met can similar organisms be combined into a species.

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View. View criteria

Vertyanov S. Yu.

Distinguishing supraspecific taxa is, as a rule, quite easy, but a clear distinction between the species themselves encounters certain difficulties. Some species occupy geographically separated areas of habitat (ranges) and therefore do not interbreed, but in artificial conditions give fertile offspring. Linnean's brief definition of a species as a group of individuals that freely interbreed and produce fertile offspring does not apply to organisms that reproduce parthenogenetically or asexually (bacteria and unicellular animals, many higher plants), as well as to extinct forms.

The set of distinguishing features of a species is called its criterion.

The morphological criterion is based on the similarity of individuals of the same species in terms of a set of features of external and internal structure. Morphological criterion is one of the main ones, but in some cases morphological similarity is not enough. The malarial mosquito was previously referred to as six non-interbreeding similar species, of which only one carries malaria. There are so-called twin species. Two species of black rats, outwardly almost indistinguishable, live separately and do not interbreed. The males of many creatures, such as birds (bullfinches, pheasants), outwardly bear little resemblance to females. Adult male and female threadtail eels are so dissimilar that for half a century scientists placed them in different genera, and sometimes even in different families and suborders.

Physiological and biochemical criterion

It is based on the similarity of the life processes of individuals of the same species. Some species of rodents have the ability to hibernate, while others do not. Many related plant species differ in their ability to synthesize and accumulate certain substances. Biochemical analysis makes it possible to distinguish between types of unicellular organisms that do not reproduce sexually. Anthrax bacilli, for example, produce proteins that are not found in other types of bacteria.

The possibilities of the physiological-biochemical criterion are limited. Some proteins have not only species, but also individual specificity. There are biochemical signs that are the same in representatives of not only different species, but even orders and types. Physiological processes can proceed in a similar way in different species. Thus, the intensity of metabolism in some arctic fish is the same as in other fish species of the southern seas.

Genetic criterion

All individuals of the same species have a similar karyotype. Individuals of different species have different chromosome sets, cannot interbreed and live in natural conditions separately from each other. Two twin species of black rats have a different number of chromosomes - 38 and 42. The karyotypes of chimpanzees, gorillas and orangutans differ in the arrangement of genes in homologous chromosomes. The differences between the karyotypes of bison and bison, which have 60 chromosomes in the diploid set, are similar. Differences in the genetic apparatus of some species can be even more subtle and consist, for example, in the different nature of the switching on and off of individual genes. The use of only a genetic criterion is sometimes insufficient. One species of weevil combines diploid, triploid and tetraploid forms, the house mouse also has different sets of chromosomes, and the gene for the human nuclear histone H1 protein differs from the homologous pea gene by only one nucleotide. Such variable DNA sequences have been found in the genome of plants, animals and humans that people can distinguish between brothers and sisters by them.

Reproductive criterion

(Latin reproducere reproduce) is based on the ability of individuals of the same species to produce fertile offspring. An important role in crossing is played by the behavior of individuals - the mating ritual, species-specific sounds (birdsong, grasshoppers chirping). By the nature of the behavior, individuals recognize the marriage partner of their species. Individuals of similar species may not interbreed due to inconsistencies in mating behavior or inconsistencies in breeding sites. So, females of one species of frogs spawn along the banks of rivers and lakes, and the other - in puddles. Similar species may not interbreed due to differences in mating periods or mating periods when living in different climatic conditions. Different periods of flowering in plants prevent cross-pollination and serve as a criterion for belonging to different species.

Reproductive criterion is closely related to genetic and physiological criteria. The viability of gametes depends on the feasibility of conjugation of chromosomes in meiosis, and hence on the similarity or difference in the karyotypes of crossing individuals. Difference in daily physiological activity (daytime or nocturnal lifestyle) sharply reduces the possibility of crossing.

The use of only the reproductive criterion does not always make it possible to clearly distinguish species. There are species that are clearly distinguishable by morphological criteria, but which, when crossed, give fertile offspring. From birds, these are some species of canaries, finches, from plants - varieties of willows and poplars. A representative of the order of artiodactyl bison lives in the steppes and forest-steppes of North America and never in natural conditions meets the bison living in the forests of Europe. In zoo conditions, these species produce fertile offspring. Thus, the population of European bison, which was practically exterminated during the world wars, was restored. Yaks and cattle, polar and brown bears, wolves and dogs, sables and martens interbreed and give fertile offspring. In the plant kingdom, interspecific hybrids are even more common, among plants there are even intergeneric hybrids.

Ecological and geographical criterion

Most species occupy a certain territory (range) and an ecological niche. Buttercup caustic grows in meadows and fields, in more damp places another species is common - creeping buttercup, along the banks of rivers and lakes - burning buttercup. Similar species living in the same range may differ in ecological niches - for example, if they eat different foods.

The use of the ecological-geographical criterion is limited by a number of reasons. The range of the species may be discontinuous. The species range of the white hare is the islands of Iceland and Ireland, the north of Great Britain, the Alps and north-west Europe. Some species have the same range, such as two species of black rats. There are organisms that are distributed almost everywhere - many weeds, a number of insect pests and rodents.

The problem of species definition sometimes grows into a complex scientific problem and is solved using a set of criteria. Thus, a species is a collection of individuals occupying a certain area and possessing a single gene pool, providing hereditary similarity of morphological, physiological, biochemical and genetic traits, interbreeding under natural conditions and producing fertile offspring.

Bibliography

For the preparation of this work, materials from the site http://www.portal-slovo.ru were used.

Studying the composition of DNA is an important task. The availability of such information makes it possible to identify the characteristic features of all living organisms and study them.

Definition

The species is the main form of organization of terrestrial life. It is he who is considered the main unit of classification of biological objects. Those problems that are associated with this term are best analyzed in a historical aspect.

History pages

The term "view" has been used since ancient times to characterize objects. Carl Linnaeus (Swedish naturalist) proposed to use this term to characterize the discreteness of biological diversity.

When identifying species, differences between individuals in terms of the minimum number of external parameters were taken into account. This method was called the typological approach. When assigning an individual to a species, its characteristics were compared with the description of those species that were already known.

In cases where it was not possible to make a comparison according to ready-made diagnoses, a new species was described. In some cases, incidental situations arose: females and males belonging to the same species were described as representatives of different classes.
By the end of the 19th century, when there was already enough information about mammals and birds living on our planet, the main problems of the typological approach were identified.

In the last century, genetics has developed significantly, so the species began to be considered as a population that has a unique similar gene pool that has a certain “protection system” for its integrity.

It was in the 20th century that similarity in biochemical parameters became the basis of the concept of species, the author of which was Ernst Mayer. Such a theory described in detail the biochemical criterion of the species.

Reality and appearance

Ch. Darwin's book "The Origin of Species" deals with the possibility of mutual transformation of species, the gradual "emergence" of organisms with new features.

View criteria

By them is meant the sum of some features inherent in only one species. Each has its own characteristic parameters that need to be analyzed in more detail.

The physiological criterion is the similarity of life processes, for example, reproduction. Interbreeding between members of different species is not expected.

The morphological criterion implies an analogy in the external and internal structure of individuals of the same species.

The biochemical criterion of species is related to the specificity of nucleic acids and proteins.

Assumes a specific set of chromosomes that differ in structure, structure complexity.

The ethological criterion is related to the habitat. Each species has its own areas of occurrence in the natural environment.

Main features

A species is considered a qualitative stage of living nature. It can exist as a result of various intraspecific relationships that ensure its evolution and reproduction. Its main feature is a certain stability of the gene pool, which is maintained by the reproductive isolation of some individuals from other similar species.

To maintain unity, free interbreeding between individuals is used, leading to a constant flow of genes within the tribal community.

Each species for several generations adapts to the conditions of a certain area. The biochemical criterion of a species involves a gradual restructuring of its genetic structure, caused by evolutionary mutations, recombinations, and natural selection. Such processes lead to the heterogeneity of the species, its disintegration into races, populations, subspecies.

To achieve genetic isolation, it is necessary to separate related groups by seas, deserts, and mountain ranges.

The biochemical criterion of a species is also associated with ecological isolation, which consists in a mismatch in the timing of reproduction, the habitation of animals in different tiers of the biocenosis.

If interspecific crossing occurs or hybrids with weakened characteristics appear, then this is an indicator of the qualitative isolation of the species, its reality. K. A. Timiryazev believed that a species is a strictly defined category that does not involve modifications, and therefore does not exist in real nature.

The ethological criterion explains the process of evolution in living organisms.

population

The biochemical criterion of a species, examples of which can be considered for different populations, is of particular importance for the development of a species. Within the range, individuals of the same species are distributed unevenly, since in wildlife there are no identical conditions for reproduction and existence.

For example, mole colonies spread only in separate meadows. There is a natural decay of the population of the species into populations. But such distinctions do not remove the possibility of crossing between individuals located in the border areas.

The physiological criterion is also connected with the fact that it undergoes significant fluctuations in different seasons and years. A population is a form of existence in certain environmental conditions, it is rightfully considered a unit of evolution.

They exist for a long time period in some part of the range, to some extent isolated from other populations. What is the biochemical criterion of a species? If individuals of the same population have a significant number of similar traits, internal crossing is allowed. Despite this process, populations are characterized by genetic heterogeneity due to the constantly emerging hereditary variability.

Darwinian divergence

How does the theory of divergence of characteristics of the properties of descendants explain the biochemical criterion of a species? Examples of different populations prove the possibility of existence with external homogeneity of a significant number of differences in genetic traits. This is what allows the population to evolve. Survive under harsh natural selection.

View types

The division is based on two criteria:

• morphological, which involves identifying differences between species;
• evaluating the degree of genetic individuality.

When describing new species, some difficulties often arise, which are associated with the incompleteness and gradualness of the process of speciation, as well as with the ambiguous correspondence of the criteria to each other.

The biochemical criterion of which has different interpretations, allows us to distinguish such "types":

• monotypic is distinguished by an unbroken vast range, in which geographical variability is weakly expressed;
• polytypic implies the inclusion of several subspecies at once, isolated geographically;
• polymorphic implies the existence within one population of several morpho-groups of individuals that differ significantly in color, but can interbreed. The genetic basis of the phenomenon of polymorphism is quite simple: the differences between morphs are explained by the influence of different alleles of the same gene.

Examples of polymorphism

Adaptive polymorphism can be considered using the praying mantis as an example. It is characterized by the existence of brown and green morphs. The first option is difficult to detect on green plants, and the second one is perfectly camouflaged in dry grass, tree branches. When mantises of this species were transplanted to a different background, adaptive polymorphism was observed.

Let us consider hybridogenic polymorphism using the example of the Spanish wheatear. Males of this species are in black-throated and white-throated morphs. Depending on the characteristics of the area, this ratio has certain differences. As a result of laboratory studies, a hypothesis was put forward about the formation of the black-throated morph in the process of hybridization with the bald wheatear.

Species-twins

They can live together, but there is no crossing between them, weak morphological differences are observed. The problem of distinguishing such species is determined by the difficulty of identifying their diagnostic characteristics, since such twin species are well versed in their “taxonomy”.

A similar phenomenon is typical for those groups of animals that use smell when searching for a partner, for example, rodents, insects. Only in some cases, a similar phenomenon is observed in organisms that use acoustic and visual signaling.

Crossbills pine and spruce are an example of twin species among birds. They are characterized by cohabitation over a large area that covers the Scandinavian Peninsula and Northern Europe. But, despite this, interbreeding is not typical for birds. The main morphological differences between them are in the size of the beak; it is significantly thicker in the pine.

Semispecies

Taking into account that the process of speciation is long and thorny, such forms may appear in which it is rather problematic to distinguish the status. They did not become a separate species, but they can be called a semi-species, since there are significant morphological differences between them. Biologists call such forms "borderline cases", "semi-species". In nature, they are quite common. For example, in Central Asia, the common sparrow coexists with the black-breasted sparrow, which is close to it in characteristics, but has a different color.

Despite the same habitat, there is no hybridization between them. In Italy, there is a different form of sparrow, which appeared as a result of the hybridization of the Spanish and the brownie. In Spain they exist together, but hybrids are considered rare.

Finally

In order to explore the diversity of life, man had to create a certain system of classification of organisms for dividing them into separate species. View is the minimum structural unit that has developed historically.

It is characterized as a set of individuals similar in physiological, morphological, biochemical characteristics, giving high-quality offspring adapted to specific environmental conditions. Such signs allow biologists to conduct a clear classification of living organisms.