View- a set of individuals with hereditary similarity of morphological, physiological and biological characteristics, freely interbreeding and producing offspring, adapted to certain living conditions and occupying a certain area in nature.

Species are stable genetic systems, since in nature they are separated from each other by a number of barriers.

A species is one of the main forms of organization of living things. However, determining whether given individuals belong to the same species or not can sometimes be difficult. Therefore, to decide whether individuals belong to a given species, a number of criteria are used:

Morphological criterion- the main criterion based on external differences between species of animals or plants. This criterion serves to separate organisms that clearly differ in external or internal morphological characteristics. But it should be noted that very often there are very subtle differences between species that can only be revealed through long-term study of these organisms.

Geographical criterion– is based on the fact that each species lives within a certain space (). The range is the geographical boundaries of the distribution of a species, the size, shape and location of which is different from the ranges of other species. However, this criterion is also not universal enough for three reasons. Firstly, the ranges of many species coincide geographically, and secondly, there are cosmopolitan species, for which the range is almost the entire planet (orca whale). Thirdly, for some rapidly spreading species (house sparrow, house fly, etc.), the range changes its boundaries so quickly that it cannot be determined.

Ecological criterion– assumes that each species is characterized by a certain type of nutrition, habitat, timing, i.e. occupies a certain niche.
The ethological criterion is that the behavior of animals of some species differs from the behavior of others.

Genetic criterion- contains the main property of the species - its isolation from others. Animals and plants of different species almost never interbreed. Of course, a species cannot be completely isolated from gene flow from closely related species, but it maintains a constant genetic composition over a long period of time. The clearest boundaries between species are from a genetic point of view.

Physiological-biochemical criterion– this criterion cannot serve as a reliable way to distinguish species, since the main biochemical processes occur in the same way in similar groups of organisms. And within each species there is big number adaptations to specific living conditions by changing the course of physiological and biochemical processes.
According to one of the criteria, it is impossible to accurately distinguish between species. It is possible to determine whether an individual belongs to a specific species only on the basis of a combination of all or most of the criteria. Individuals occupying certain territory and freely interbreeding are called a population.

Population– a collection of individuals of the same species occupying a certain territory and exchanging genetic material. The set of genes of all individuals in a population is called the gene pool of the population. In each generation, individual individuals contribute more or less to the overall gene pool, depending on their adaptive value. The heterogeneity of the organisms included in the population creates the conditions for action, therefore the population is considered the smallest evolutionary unit from which the transformation of the species begins. The population, therefore, represents a supraorganismal formula for the organization of life. A population is not a completely isolated group. Sometimes interbreeding occurs between individuals from different populations. If some population turns out to be completely geographically or ecologically isolated from others, then it can give rise to a new subspecies, and subsequently a species.

Each population of animals or plants consists of individuals of different sexes and different ages. The ratio of the number of these individuals may vary depending on the time of year, natural conditions. The size of a population is determined by the ratio of birth and death rates of its constituent organisms. If these indicators are equal for a sufficiently long time, then the population size does not change. Environmental factors and interaction with other populations can change the population size.

The genetic (cytogenetic) criterion of a species, along with others, is used to distinguish elementary systematic groups and analyze the state of the species. In this article we will consider the characteristics of the criterion, as well as the difficulties that a researcher applying it may encounter.

IN different industries Biological science defines species in its own way. From an evolutionary perspective, we can say that a species is a collection of individuals that have similarities external structure and internal organization, physiological and biochemical processes, capable of unlimited interbreeding, leaving fertile offspring and genetically isolated from similar groups.

A species can be represented by one or several populations and, accordingly, have an integral or dissected range (territory/habitat)

Type nomenclature

Each species has its own name. According to the rules of binary nomenclature, it consists of two words: a noun and an adjective. A noun is a generic name, and an adjective is a specific name. For example, in the name "Dandelion officinalis", the species "medicinal" is one of the representatives of plants of the genus "Dandelion".

Individuals of related species within the genus have some differences in appearance, physiology, and environmental preferences. But if they are too similar, then their species identity is determined by the genetic criterion of the species based on the analysis of karyotypes.

Why does a species need criteria?

Carl Linnaeus, who was the first to give modern names and describe many species of living organisms, considered them unchanged and non-variable. That is, all individuals correspond to a single species image, and any deviations from it are an error in the implementation of the species idea.

From the first half of the 19th century century, Charles Darwin and his followers substantiate a completely different concept of species. In accordance with it, the species is variable, heterogeneous and includes transitional forms. The constancy of a species is relative, it depends on the variability of conditions environment. The elementary unit of existence of a species is a population. It is reproductively isolated and meets the genetic criterion of the species.

Given the heterogeneity of individuals of the same species, it can be difficult for scientists to determine the species identity of organisms or distribute them between systematic groups.

Morphological and genetic criteria of a species, biochemical, physiological, geographical, ecological, behavioral (ethological) - all these are complexes of differences between species. They determine the isolation of systematic groups, their reproductive discreteness. And from them one can distinguish one species from another, establish the degree of their relationship and position in the biological system.

Characteristics of the genetic criterion of the species

The essence of this trait is that all individuals of the same species have the same karyotype.

A karyotype is a kind of chromosomal “passport” of an organism; it is determined by the number of chromosomes present in mature somatic cells of the body, their size and structural features:

• chromosome arm length ratio;
• the position of the centromeres in them;
• the presence of secondary constrictions and satellites.

Individuals belonging to different species will not be able to interbreed. Even if it is possible to obtain offspring, as with a donkey and a horse, a tiger and a lion, then interspecific hybrids will not be fertile. This is explained by the fact that the halves of the genotype are not the same and conjugation between chromosomes cannot occur, so gametes are not formed.

In the photo: a mule is a sterile hybrid of a donkey and a mare.

Object of study - karyotype

The human karyotype is represented by 46 chromosomes. In most species studied, the number of individual DNA molecules in the nucleus that form chromosomes falls within the range of 12 - 50. But there are exceptions. The fruit fly Drosophila has 8 chromosomes in its cell nuclei, and the small representative of the Lepidoptera family Lysandra has a diploid chromosome set of 380.

An electron micrograph of condensed chromosomes, which allows one to evaluate their shape and size, reflects the karyotype. Analysis of the karyotype as part of the study of genetic criteria, as well as comparison of karyotypes with each other, helps determine the species identity of organisms.

When two species are as one

A common feature of type criteria is that they are not absolute. This means that using only one of them may not be sufficient for precise definition. Organisms that are outwardly indistinguishable from each other may turn out to be representatives of different species. Here the genetic criterion comes to the aid of the morphological. Examples of doubles:

1. Today there are two known species of black rats, which were previously identified as one due to external identity.
2. There are at least 15 species of malaria mosquitoes, which are distinguishable only through cytogenetic analysis.
3. In North America, 17 species of crickets have been found that have genetic differences, but are phenotypically classified as a single species.
4. It is believed that among all bird species there are 5% duplicates, for identification of which a genetic criterion must be used.
5. Confusion in the taxonomy of mountain bovids has been cleared up thanks to karyological analysis. Three types of karyotypes have been identified (mouflons have 2n=54, argali and argali have 56, urials have 58 chromosomes each).

One species of black rat has 42 chromosomes, the karyotype of another is represented by 38 DNA molecules.

When one view is like two

For species groups with large area range and the number of individuals, when there is geographic isolation within them or individuals have a wide ecological valency, the presence of individuals with different karyotypes is characteristic. This phenomenon is another variant of exceptions in the genetic criteria of the species.

Examples of chromosomal and genomic polymorphism are common in fish:

• in rainbow trout, the number of chromosomes varies from 58 to 64;
• two karyomorphs, with 52 and 54 chromosomes, were found in White Sea herring;
• with a diploid set of 50 chromosomes, representatives of different populations of silver crucian carp have 100 (tetraploids), 150 (hexaploids), 200 (octaploids) chromosomes.

Polyploid forms are found in both plants (goat willow) and insects (weevils). House mice and gerbils can have different numbers of chromosomes that are not a multiple of the diploid set.

Doubles by karyotype

Representatives of different classes and types may have karyotypes with the same number of chromosomes. There are much more such coincidences among representatives of the same families and genera:

1. Gorillas, orangutans and chimpanzees have a karyotype consisting of 48 chromosomes. The differences cannot be determined by appearance; here you need to compare the order of nucleotides.
2. There are minor differences in the karyotypes of the North American bison and the European bison. Both have 60 chromosomes in the diploid set. They will be classified as one species if analyzed only by genetic criteria.
3. Examples of genetic twins are also found among plants, especially within families. Among willows, it is even possible to obtain interspecific hybrids.

To identify subtle differences in genetic material in such species, it is necessary to determine the gene sequences and the order in which they are inserted.

Impact of mutations on criterion analysis

The number of chromosomes in a karyotype can be changed as a result of genomic mutations - aneuploidy or euploidy.

With aneuploidy, one or more additional chromosomes appear in the karyotype, and there may also be a number of chromosomes less than that of a full-fledged individual. The reason for this disorder is the nondisjunction of chromosomes at the stage of gamete formation.

The figure shows an example of aneuploidy in humans (Down syndrome).

Zygotes with a reduced number of chromosomes, as a rule, do not begin to fragment. And polysomic organisms (with “extra” chromosomes) may well turn out to be viable. In the case of trisomy (2n+1) or pentasomy (2n+3), an odd number of chromosomes will indicate an anomaly. Tetrasomy (2n+2) can lead to an actual error in determining the species based on genetic criteria.

Multiplication of the karyotype - polyploidy - can also mislead the researcher when the karyotype of the mutant represents the sum of several diploid sets of chromosomes.

Criterion Difficulty: Elusive DNA

The diameter of the DNA strand in the untwisted state is 2 nm. The genetic criterion determines the karyotype in the period preceding cell division, when thin DNA molecules are repeatedly helicalized (condensed) and form dense rod-shaped structures - chromosomes. The thickness of a chromosome is on average 700 nm.

School and university laboratories are usually equipped with microscopes with low magnification (from 8 to 100); it is not possible to examine the details of the karyotype in them. The resolution of a light microscope, in addition, allows you to see objects no less than half the length of the shortest light wave at any, even the highest magnification. The shortest length is for waves purple(400 nm). This means that the smallest object visible in a light microscope will be from 200 nm.

It turns out that the colored decondensed chromatin will appear as cloudy areas, and the chromosomes will be visible without detail. An electron microscope with a resolution of 0.5 nm allows you to clearly see and compare different karyotypes. Considering the thickness of filamentous DNA (2 nm), it will be clearly visible under such a device.

Cytogenetic criterion at school

For the reasons described above, the use of microslides for laboratory work According to the genetic criterion of the species, it is inappropriate. In assignments, you can use photographs of chromosomes obtained under an electron microscope. For convenience, in the photo, individual chromosomes are combined into homologous pairs and arranged in order. This diagram is called a karyogram.

Sample assignment for laboratory work

Exercise. Look at the given photographs of karyotypes, compare them and draw a conclusion about whether the individuals belong to one or two species.

Photos of karyotypes for comparison in laboratory work.

Working on a task. Calculate total chromosomes in each karyotype photo. If they match, compare them by appearance. If it is not a karyogram, among the chromosomes of average length, find the shortest and longest in both images, compare them by size and location of the centromeres. Draw a conclusion about the differences/similarities of karyotypes.

Answers to the task:

1. If the number, size and shape of chromosomes match, then the two individuals whose genetic material is presented for study belong to the same species.
2. If the number of chromosomes differs by a factor of two, and chromosomes of the same size and shape are found in both photographs, then most likely the individuals are representatives of the same species. These will be karyotypes of diploid and tetraploid forms.
3. If the number of chromosomes is not the same (differs by one or two), but in general the shape and size of the chromosomes of both karyotypes are the same, we're talking about about normal and mutant forms of one species (the phenomenon of aneuploidy).
4. At different quantities chromosomes, as well as discrepancies in size and shape characteristics, the criterion will classify the presented individuals as two different species.

The conclusion must indicate whether it is possible to determine the species identity of individuals based on the genetic criterion (and only it).

Answer: it is impossible, since any species criterion, including genetic, has exceptions and can give an erroneous determination result. Accuracy can only be guaranteed by applying a set of type criteria.

The question of species and criteria for species occupies a central place in the theory of evolution and is the subject of numerous studies.knowledge in the field of taxonomy, zoology, botany and othersSci. And this is understandable: a clear understanding of the essencespecies is necessary to clarify the mechanisms of evolutionary process.

A strict generally accepted definition of species has not yet been developed.nerdy. In biological encyclopedic dictionary we are onWe use the following definition of the form:

“A species is a set of populations of individuals capable of interbreedingniyu with the formation of fertile offspring inhabiting the definitionnative habitat, having a number of common morphophysiological characteristics and individuals that are distant from other similar groups of individuals are practicallypurely by the complete absence of hybrid forms.”

Compare this definition with the one given in your textbook(textbook by A.A. Kamensky, § 4.1, p. 134).

Let us explain the concepts that occur. in the definition of the form:

Area— area of ​​distribution of a given species or population in nature.

Population(from Latin “por uius” " - people, population) - totalitythe number of individuals of the same species having a common gene pool and historylocating a certain territory - habitat.

Gene pool- a set of genes that individuals haveof this population.

Let us consider the history of the development of views on species in biology.

The concept of species was first introduced into science by an English botanist John Ray inXVII century. The seminal work on the species problemwas written by a Swedish naturalist and naturalistCarl Linnaeus in XVIII century, in which he proposed the firstscientific definition of the species, clarified its criteria.

K. Linnaeus believed that the species is a universalsebaceous, actually existing unit of living matter, morphologically homogeneous and unchanging . All individuals of the species, according to the scientist, have a typical morphological appearance, and variations represent random deviations , the result of an imperfect embodiment of the idea of ​​the form (a kind of deformity). Scientistbelieved that species are unchangeable, nature is unchangeable. The idea is unchangednew nature was based on the concept of creationism, according toby which all things were created by God. Applied to biologyLinnaeus expressed this concept in his famousmule “There are as many species as different forms first produced the Infinite creature".

Another concept belongs to Tom Baptiste Lamarck- ledto a French naturalist. According to his concept, the views are real Not exist, is a purely speculative concept invented forin order to make it easier to consider collectively a larger number ofindividuals, since, according to Lamarck, “in nature there is noanything other than individuals.” Individual variability is continuous, therefore, the boundary between species can be drawn both here and there - where is more convenient.

The third concept was prepared in the first quarter XIX century. It was justified Charles Darwin and subsequent biologistsmi. According to this concept, species have an independent reality. Viewheterogeneous, is a system of subordinate units. WITHAmong them, the basic elementary unit is the population. Types, by Darwin, change, they are relatively constant and are resthe result of evolutionary development .

Thus, the concept of “species” has a long history of development in biological science.

Sometimes the most experienced biologists are stumped when determiningwhether these individuals belong to the same species or not . Why is that happens, are there precise and strict criteria thatCould you resolve all doubts?

Species criteria are the characteristics by which one species is distinguishedcomes from someone else. They are also isolating mechanisms.preventing interbreeding, independence, independent sti species.

We know that one of the main features of biological matter on our planet is discreteness. This is in is expressed in the fact that it is represented by separate species, notinterbreeding with each other, isolated from each other gogo.

The existence of a species is ensured by its genetic unity(individuals of a species are capable of interbreeding and producing viable fertile offspring) and its genetic independence (impossiblepossibility of crossing with individuals of another species, not viablepresence or sterility of hybrids).

The genetic independence of a species is determined by a combination ofthe fullness of it characteristic features: morphological, physiological, biochemical, genetic, lifestyle features, behavior, geographical distribution, etc. This is crit series of the species.

Type criteria

Morphological criterion

The morphological criterion is the most convenient and noticeable, thereforeand is now widely used in the taxonomy of plants and animals.

We can easily distinguish by the size and color of the plumage of the greatspotted woodpecker from green woodpecker, lesser spotted woodpecker and yellow woodpecker(black woodpecker), great tit from tufted, long-tailed, blueand chickadees, meadow clover from creeping and lupine, etc.

Despite its convenience, this criterion does not always work. You can’t use it to differentiate sibling species, practically notdifferent morphologically. There are many such species among malariamosquitoes, fruit flies, whitefish. Even in birds, 5% of species are twins, andThere are 17 of them in one row of North American crickets.

The use of morphological criteria alone canlead to erroneous conclusions. So, C. Linnaeus in particularexternal structure classified the male and female mallard duck as different species. Siberian hunters have identified five variations based on the fur color of foxes: greyhounds, moths, crosses, black-brown and black. In England, 70 species of butterflies, along with individuals with light colors, also haveny morphs, the number of which in populations began to increase inconnection with forest pollution. Polymorphism is widespreadphenomenon. It occurs in all species. It also affects the characteristics by which species differ. In woodcutter beetles, for example, in the longhorned beetle,exact, meeting late spring on the swimsuit, besides the teeIn the peak form, up to 100 color aberrations occur in populations. During the time of Linnaeus morphological criterion was in charge, becauseshowed that there is one typical form for the species.

Now that it has been established that a species can have many forms, likethe logical concept of species is discarded and the morphological criterion is notalways satisfies scientists. However, it should be recognized that this criterionIt is very convenient for systematizing species and in most keys to animals and plants it plays a major role.

Physiological criterion

Physiological features various types plants and bellygenetics are often a factor ensuring their genetic selfworthiness. For example, many fruit flies have sperm from individuals of foreign species.Yes, it causes an immunological reaction in the female genital tract, which leads to the death of sperm. Hybridization of various species andsubspecies of goats often leads to disruption of the periodicity of fruitwearing - the offspring appears in winter, which leads to its death. Crossesthe formation of different subspecies of roe deer, for example Siberian and European,sometimes leads to the death of females and offspring due to their large size fetus

Biochemical criterion

Interest in this criterion has appeared in recent decades due todevelopment of biochemical research. It is not widely used, since there are no specific substances characteristiconly for one species and, in addition, it is very labor-intensive and far not universal. However, it can be used in cases wherewhen other criteria “do not work”. For example, for two twin speciesbutterflies from the genus amata (A. r h e g ea and A. g ugazzii ) diagnosticand the signs are two enzymes - phosphoglucomutase and esterase-5, allowing able to even identify hybrids of these two species. IN Lately comparative study of the composition of DN has become widespreadK in practical taxonomy of microbes. Studying the composition of DNA made it possible revise the phylogenetic system of various groups microorganisms. The developed methods make it possible to compare the compositionDNA in bacteria conserved in the earth and living todayforms For example, a comparison was made of the DNA composition of agedabout 200 million years in the thickness of the salts of the Paleozoic bacterium pseudosalt-loving monads and living pseudomonads. The composition of their DNA turned out to be identical, and the biochemical properties are similar.

Cytological criterion

The development of cytological methods allowed scientists to study the backgroundrmu and the number of chromosomes in many species of animals and plants. A new direction has emerged - karyosystematics, which has introduced someamendments and clarifications to the phylogenetic system constructed on the basis of morphological criteria. In some cases, the number of chromosomes serves characteristic feature kind. Karyological analysis allowed, for example, to streamline the taxonomy of wild mountain sheep, whichVarious researchers have identified from 1 to 17 species. The analysis showedthe presence of three karyotypes: 54 chromosome - in mouflons, 56romosomal - in argali and argali and 58-chromosomal - in the inhabitantsmountains Central Asia— urials.

However, this criterion is not universal. Firstly, atIn many different species, the number of chromosomes is the same and their shape is similar. Secondly, within the same species there may be individuals with different numbers chromosomes. These are the so-called chromosomal and genomicpolymorphism. For example, goat willow has diploid - 38 and tetraploid The number of chromosomes is 76. In silver crucian carp there are populations with a setrom chromosomes 100, 150, 200, while the normal number is 50. In rainbow trout, the number of chromosomes varies from 58 to 64, in the White SeaThere are also individuals with 52 and 54 chromosomes. In Tajikistan on the sitewith a length of only 150 km, zoologists discovered a population of mole voles with a set of chromosomes from 31 to 54. Gerbils from different habitats have a different number of chromosomes: 40 - in Algerian gerbils Chinese populations, 52 - among Israeli and 66 - among Egyptian populations. To infusion Currently, intraspecific chromosomal polymorphism has been found in 5% of c.ito-genetically studied mammalian species.

Sometimes this criterion is misinterpreted as genetic. Undoubtedly, the number and shape of chromosomes is an important feature that prevents crossbreedingunderstanding of individuals of different species. However, this is rather cytomorphologicalimportant criterion, since we are talking about intracellular morphology: the numberand the shape of chromosomes, and not about the set and structure of genes.

E tological criterion

For some animal species, a mechanism that preventsbaptism and leveling the differences between them are especiallythe benefits of their behavior, especially in mating season. Partner recognition of one's own species and rejecting courtship attempts by males of another speciesbased on specific stimuli - visual, soundchemical, tactile, mechanical, etc.

In the widespread genus warbler, different species are very similarlive on each other morphologically, in nature they cannot be distinguished either by color or size. But they all differ very well in song and according to habits. The song of the willow warbler is complex, similar to the song of the chaffinch, only without his final knee, and the chiffchaff song is aboutTiny monotonous whistles. Numerous sibling species of ameRican fireflies from the genus P hotinus were first identified only bydifferences in their light signals. Male fireflies in flight flashes of light, the frequency, duration and alternation of whichspecific for each species. Well known but that a number of species of Orthoptera and Homoptera living within,same biotope and reproducing synchronously, differ onlythe nature of their calling signals. Such twin species with acousticreproductive isolation is found, for example, in crickets, pipits, cicadas and other insects. Two closely related species of AmericanToads also do not interbreed due to differences in male calls.

Differences in display behavior often play a decisive role in reproductive isolation. For example, closely related species of Drosophila flies fromare characterized by the specifics of the courtship ritual (by the nature of vibrationwings, trembling legs, circling, tactile contacts). Two closespecies - the herring gull and the black whale have differences in the degree of pronouncedsty of demonstrative poses, and seven species of lizards of the genus S se1rogs differ in the degree of head raising when courting sexual partners.

Ecological criterion

Features of behavior are sometimes closely related to the ecological specifics of the species, for example, with the features of the nest structure. Three species of our common tits nest in hollows of deciduous trees, mainly birches. The great tit in the Urals usually chooses deep hollow in the lower part of the trunk of a birch or alder, formed in the as a result of rotting of a knot and adjacent wood. This hollow is inaccessible to woodpeckers, crows, and predatory mammals. Tit Muscovy inhabits frost cracks in birch and alder trunks. HaThe chick prefers to build a hollow itself, plucking out cavities in the rottingold or old trunks of birch and alder, and without this labor-intensive procedure it will not lay eggs.

Features of the lifestyle inherent in each species determineits position, its role in the biogeocenosis, that is, its ecologicalniche. Even the closest species, as a rule, occupy different econiches, that is, they differ in at least one or two ecological signs.

Thus, the economic niches of all our species of woodpeckers differ in their feeding patterns. Great spotted woodpecker feeds on larch seeds in winter Tsy and pine trees, crushing cones in their “forges”. black woodpeckerZhelna extracts longhorned beetle larvae and borers from under the bark and from woodfir trees, and the Lesser Spotted Woodpecker chisels the soft wood of the alder or extracts nase from the stems of herbaceous plants.

Each of the 14 species of Darwin's finches (named afterC. Darwin, who first drew attention to them), living in the Galapagos islands, has its own specific econiche, which differs from others primarily in the nature of the food and the ways of obtaining it.

Neither the ecological nor the ethological criticism discussed aboveries are not universal. Very often individuals of the same species, but onceny populations differ in a number of lifestyle featuresand behavior. And on the contrary, different species, even very distant ones, in the systemchemically, may have similar ethological signsor play the same role in the community (for example, the roles of mammal herbivores insects and insects, such as locusts, are quite comparable).

Geographical criterion

This criterion, along with the ecological one, occupies second place (after morphological) in most determinants. When identifying many species of plants, insects, birds, mammals and othersgroups of organisms whose distribution is well studied, knownThe distribution of the range plays a significant role. The subspecies' habitats, as a rule, do not coincide, which ensures their reproductive isolation and, in fact,, their existence as independent subspecies. Many typesoccupy different habitats (such species are called allopatric And). But a huge number of species have matching or overlapspreading ranges (sympatric species). In addition, there are species that are nothaving clear boundaries of distribution, as well as spit speciesmopolitans, living over vast expanses of land or ocean. INDue to these circumstances, the geographical criterion cannot be used universal.

Genetic criterion

Genetic unity of the species and, accordingly, genetic isolationit from other species is the main criterion of the species, the main speciesa sign caused by a complex of structural and life featuresactivities of organisms of this species. Genetic compatibilitybridge, similarity of morphological, physiological, cytologicaland other signs, identical behavior, living together - all thiso creates the necessary conditions for successful reproduction and restorationproduction of the species. At the same time, all these characteristics provide geneticisolation of a species from other similar species. For example, oncelyricism in the song of thrushes, warblers, warblers, finches and finch, deafand common cuckoos prevent the formation of mixed pairs,despite the similarity of their coloring and ecology (in birds with a specific song, hybrids are almost never found). Even in those cases I, when, despite isolation barriers, crossing occurredtion of individuals of different species, a hybrid population, as a rule, does not arise, since a whole series of post-populationisolation mechanisms. The most important of them is the death of male gametes (genetical incompatibility), death of zygotes, non-viability of hygotesreads, their sterility, and finally, the inability to find sexualpartner and produce viable fertile offspring. We know thatEach species has its own set of specific characteristics. An interspecific hybrid will have characteristics intermediate betweensigns of two original parent forms. For example, his song will not be understood by either a finch or a finch if it is a hybrid of these species, and he will not find a sexual partner. Such a hybrid hasthe name of gametes, the chromosomes of the finch contained in its cells “do notfinch chromosomes and, not finding a homologous partner, do notconjugate. As a result, gametes with a disrupted set ofchromosomes, which are usually not viable. And as a resultThis hybrid will be sterile.

The raven is distributed throughout almost the entire northern hemisphere: it is foundalmost throughout Europe, Asia, excluding Southeast, in NorthernAfrica and North America. Everywhere he leads a sedentary lifestyle. Inhabits forests, deserts and mountains. In treeless areas it stays nearrocks, coastal cliffs river valleys. Mating and mating games onin the south of the country they are celebrated in the first half of February, in the north - inMarch. Pairs are constant. Nests are usually placed on the tops of tall trees. The clutch contains from 3 to 7, usually 4-6, bluish-green eggs ki with dark markings.

Raven is an omnivorous bird. Its main food is carrion, which it oftenfound in landfills and slaughterhouses. Eating carrion, he performslike a sanitary bird. It also feeds on rodents, eggs,and chicks, fish, various invertebrate animals, and placesmi and cereal grains.

The crow resembles a crow in general physique, but significantlysmaller than it: weighs from 460 to 690 g.

The described species is interesting in that the color of the plumage disintegratesinto two groups: gray and black. The gray crow is well knownnew two-color color: head, throat, wings, tail, beak and legs are black, the rest of the plumage is gray. The Carrion Crow is all black, with a metallic blue and purple sheen.

Each of these groups has a local distribution. The hooded crow is widespread in Europe, Western Asia, the black crow is widespread in Central and Western Europe, on the one hand, in Central, East Asia and North America on the other.

The crow inhabits the edges and outskirts of forests, gardens, groves, thickets of river valleys, and less often rocks and slopes of coastal cliffs. It is partly sedentary and partly migratory.

At the beginning of March in the southern parts of the country and in April-May in the northern and eastern parts, egg laying begins. The clutch usually contains 4-5 eggs of pale green, bluish-green or partially green color with dark spots and specks. The crow is an omnivorous bird. Among animals, it eats various invertebrates - beetles, ants, mollusks, as well as rodents, lizards, frogs and fish. From plants it pecks grains of cultivated cereals, seeds of spruce, field bindweed, bird buckwheat, etc. In winter it feeds mainly on garbage.

White hare and brown hare

The genus of hares proper, which includes the hare and hare, as well as 28 other species , quite numerous. The most famous hares in Russia are the hare and the hare.. White hare can be found on the territory from the coast of the Arctic Ocean to the southern border of the forest zone, in Siberia - to the borders with Kazakhstannom, China and Mongolia, and on Far East— from Chukotka to And North Korea. The hare is also widespread in the forests of Europe, as well as in the east of Northern America. The hare lives in the territory European Russia from Kareliafrom the south of the Arkhangelsk region to the southern borders of the country, in Ukraine and in Transnistriacasier. But in Siberia, this hare lives only in the south and west of Lake Baikal.

The hare got its name due to its snow-white winter fur. Only the tips of his ears remain black all year round. The hare in some northern areas also becomes very light in color in winter, but it is never snow-white. And in the south it does not change color at all.

The hare is more adapted to life in open landscapes, since it is larger than the hare and runs better. At short distances this hare can developspeed up to 50 km/h. The hare's paws are wide, with dense pubescence to avoid falling into loose forest snowdrifts. And the hare already has paws, after all, in open places the snow is usually hard, compacted, “trodden down by the wind.”

The body length of the white hare is 45–75 cm, weight is 2.5–5.5 kg. The ears are shorter than those of a hare. The body length of the hare is 50-70 cm, weight up to 5 (sometimes 7) kg.

Reproduce Hares are usually two, and in the south three or even four times a year. U zaiWhite hare cows may have two, three five, seven hare offspring per hatch, while hare- usually just one or two bunnies. Browns begin to try grass two weeks after birth, and whites even faster - after a week.

The belonging of individuals to a particular species is determined based on a number of criteria.

Type criteria- these are various taxonomic (diagnostic) characters that are characteristic of one species, but absent in other species. A set of characteristics by which one species can be reliably distinguished from other species is called a species radical (N.I. Vavilov).

Species criteria are divided into basic (which are used for almost all species) and additional (which are difficult to use for all species).

Basic criteria of the type

1. Morphological criterion of the species. Based on the existence of morphological characters characteristic of one species, but absent in other species.

For example: in the common 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.

Twin species. Thus, closely related species may differ in subtle characteristics. There are twin species that are so similar that it is very difficult to use a morphological criterion to distinguish them. For example, the malaria mosquito species is actually represented by nine very similar species. These species differ morphologically only in the structure of the reproductive structures (for example, the color of the eggs in some species is smooth gray, in others - with spots or stripes), in the number and branching of hairs on the limbs of the larvae, in the size and shape of the wing scales.

In animals, twin species are found among rodents, birds, many lower vertebrates (fish, amphibians, reptiles), many arthropods (crustaceans, mites, butterflies, dipterans, orthoptera, hymenoptera), mollusks, worms, coelenterates, sponges, etc.

Notes on sibling species (Mayr, 1968).

1. There is no clear distinction between common species(“morphospecies”) and sibling species: simply in sibling species morphological differences expressed to a minimum extent. Obviously, the formation of sibling species is subject to the same laws as speciation in general, and evolutionary changes in groups of sibling species occur at the same rate as in morphospecies.

2. Sibling species, when subjected to careful study, usually show differences in a number of small morphological characters (for example, male insects belonging to different species clearly differ in the structure of their copulatory organs).

3. Restructuring of the genotype (more precisely, the gene pool), leading to mutual reproductive isolation, is not necessarily accompanied by visible changes in morphology.

4. In animals, sibling species are more common if morphological differences have less impact on the formation of mating pairs (for example, if recognition uses smell or hearing); if animals rely more on vision (most birds), then twin species are less common.

5. The stability of the morphological similarity of twin species is due to the existence of certain mechanisms of morphogenetic homeostasis.

At the same time, there are significant individual morphological differences within species. For example, the common viper is represented by many color forms (black, gray, bluish, greenish, reddish and other shades). These characteristics 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) - geographical range. For example, in Europe some species malaria 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 can overlap, and then one species smoothly passes into another. In this case, a chain of vicariating species is formed (superspecies, or series), the boundaries between which can often be established only through special research (for example, herring gull, black-billed gull, western gull, Californian gull).

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

For animals, instead of the concept of “ecological niche,” the concept of “adaptive zone” is often used. For plants, the concept of “edapho-phytocenotic area” is often used.

Adaptive zone- this is a certain type of habitat with a characteristic set of specific environmental conditions, including the type of habitat (aquatic, land-air, soil, organism) and its particular features (for example, in ground-air environment habitat - the total amount of solar radiation, precipitation, relief, atmospheric circulation, distribution of these factors by season, etc.). In the biogeographical aspect, adaptive zones correspond to the largest divisions of the biosphere - biomes, which are a collection of living organisms in combination with certain living conditions in vast landscape-geographical zones. However, different groups of organisms use environmental resources differently and adapt to them differently. Therefore, within the biome of the coniferous-deciduous forest zone temperate zone One can distinguish adaptive zones of large guarding predators (lynx), large overtaking predators (wolf), small tree-climbing predators (marten), small terrestrial predators (weasel), etc. Thus, the adaptive zone is an ecological concept that occupies an intermediate position between the habitat and the ecological niche.

Edapho-phytocenotic area- this is a set of bioinert factors (primarily soil, which are an integral function of the mechanical composition of soils, topography, the nature of moisture, the influence of vegetation and microorganism activity) and biotic factors (primarily the totality of plant species) of nature that make up the immediate environment of the area of ​​interest kind of us.

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

Additional type criteria

4. Physiological-biochemical criterion. Based on the fact that different species may differ in the amino acid composition of proteins. Based on this criterion, for example, some species of gulls are distinguished (herring, black-billed, western, Californian).

At the same time, within a species there is variability in the structure of many enzymes (protein polymorphism), and different species may have similar proteins.

5. 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 durum wheats have 28 chromosomes in their 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 one species. For example, moose of Eurasian subspecies have 2n=68, and moose of North American species have 2n=70 (in the karyotype of North American moose there are 2 less metacentrics and 4 more acrocentrics). Some species have chromosomal races, for example, the black rat has 42 chromosomes (Asia, Mauritius), 40 chromosomes (Ceylon) and 38 chromosomes (Oceania).

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

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

Pacific salmon (pink salmon, chum salmon, etc.) live for two years and spawn only before dying. Consequently, the descendants of individuals that spawned in 1990 will breed only in 1992, 1994, 1996 (“even” race), and the descendants of individuals that spawned in 1991 will breed only in 1993, 1995, 1997 (“even” race). odd" race). An “even” race cannot interbreed with an “odd” one.

7. Ethological criterion. Associated with interspecific differences in behavior in animals. In birds, song analysis is widely used to recognize species. Depending on the nature of the sounds produced, different types of insects differ. Different species of North American fireflies vary in the frequency and color of their light flashes.

8. Historical criterion. Based on the study of the history of a species or group of species. This criterion is complex in nature, since it includes a comparative analysis of the modern ranges of species, analysis

In the process of practical human activity, the concept of a species was formed. When describing animals, this concept was already used by Aristotle. However, for a fairly long period it was not endowed with scientific content and was used as a logical term. The concept in question acquired the status of a classification unit in the process of development of taxonomy. John Ray (English naturalist) developed the idea of ​​a species as a component of taxonomy. At the same time, scientists identified three most important characteristics of this unit. Thus, a species, according to Ray, is a set of organisms that are characterized by a common origin. This systematic unit unites organisms that are similar in morphological and physiological characteristics. In addition, it is a self-reproducing system.

Rey considered origin the main indicator. Thus, the naturalist classified similar plants that reproduce their own kind from their seeds as one species.

A significant expansion and also its deepening occurred thanks to the work of Linnaeus, who showed that a species is a real elementary and stable unit of living nature, isolated from other species. This concept began to be used as a main and plants. However, in those days, appearance was seen as a consequence of creative action.

Lamarck proclaimed in his works the position that in nature there are unchanging systematic units of plants and animals. Species are constantly transforming, changing, moving into other species. In this regard, according to Lamarck, the old systematic unit cannot be separated from the new one. Thus, the French naturalist came to the conclusion of denying the reality of the species, while affirming the idea of ​​development.

Darwin's teaching was based on a different position. This position was scientifically substantiated. In accordance with it, the developing real species is determined by historical development under the influence. In accordance with Darwinian teaching, a comprehensive study of systematic units was carried out. Thus, a study was carried out of the morphological criterion of the species, as well as an experimental, genetic study of the structure and ways of its formation. These events were of decisive importance in substantiating the population aspect of a systematic unit as the main form of development and existence organic world generally.

Today it is believed that the organic environment includes a diversity of life forms. Moreover, “species” is a universal phenomenon for all living nature. The systematic unit under consideration is formed in the course of evolutionary transformations caused by natural selection. As a result, it represents a specific stage (link) in the development of living organisms and is the main form of existence of life on the planet.

One type differs from another by a set of common features - criteria. Together, these features form the reality of systematic units.

Morphological ones are based on the presence of certain hereditary characteristics in all individuals of one species. Individuals within the same systematic unit, in other words, have a similar external and internal structure. The morphological criterion of a species is considered a fairly convenient and simple character. Moreover, this characteristic was used by taxonomists earlier than other characteristics and was the main one for a certain period. However, it should be noted that the morphological criterion of a species is rather relative. This feature is necessary, but not sufficient. The morphological criterion of a species does not allow distinguishing systematic units that have significant similarities in structure, but do not interbreed with each other. For example, systematic twin units. Thus, the name includes about fifteen species, indistinguishable in appearance, but previously considered one species. It has been established that about 5% of all systematic units are twins. Thus, the morphological criterion of a species cannot be the only sign of difference.