Characteristics of type criteria. The geographical criterion of a species is its Relative to the criterion of the species

Morphological criterion reflects the external and internal similarity of individuals of the same species.

Thus, black and white crows belong to different species, which can be determined by their appearance. But organisms that belong to the same species may differ from each other in some characteristics and properties. However, these differences are very small compared to those observed in individuals of different species. Meanwhile, there are species that have external resemblance, but cannot interbreed with each other. These are the so-called twin species. Thus, in Drosophila, the malaria mosquito and the black rat, two twin species have been identified. Twin species are also found in amphibians, reptiles, birds and even mammals. Consequently, the morphological criterion is not decisive for distinguishing species. However this criterion for a long time was considered the main and only one in determining species (Fig. 39).

At the core physiological criterion lies the similarity of life processes in individuals of each species, especially reproduction.

Representatives of different species do not interbreed with each other, and if they interbreed, they do not produce offspring. The non-breeding of species is explained by differences in the structure of the genital organs, different terms reproduction and other reasons. However, in nature there are cases when some species of plants (poplar, willow), birds (canary) and animals (hares) can interbreed and produce offspring. This also indicates that one physiological criterion is also not enough to distinguish between species.

This criterion refers to the specific environmental conditions in which individuals of a particular species live and to which they have adapted. For example, poisonous buttercup grows in fields and meadows, creeping buttercup grows in wet places, and burning buttercup grows along the banks of rivers and reservoirs, and in swampy places.

This criterion refers to the set of chromosomes, structure and color characteristic of each species. One look-alike black rat has 38, the other has 42 chromosomes. Although the genetic criterion is characterized by some constancy, this similarity is relative, since within a species there may be differences in the number and structure of chromosomes. In addition, the number of chromosomes may be the same in different species. For example, cabbage and radish each have 18 chromosomes.

Species criteria determine how strongly the traits and properties are expressed that distinguish one species from another.

A species is considered to be a historically formed association of populations, where individuals are endowed with genetic conformity, morphological and physiological similarity, freedom of crossing and further reproduction, and reside in a certain area under special living conditions.

Genetic (genetic-reproductive) criterion of the species

Genetic connection is the initial reason for the external similarity of organisms and primary symptom to unite into a separate set of individuals.

Individuals within one species are characterized by a certain set of chromosomes, their quantitative value, size and external outline.

The cytogenetic criterion is the most important characteristic of the species. Due to the different sets of chromosomes, living organisms of different species adhere to special isolation in the production of offspring and are not able to interbreed.

The study of the shape and number of chromosomes is performed using the cytological method. Number structural elements cell nucleus - distinguishing feature kind.

Morphological criterion of the species

According to the morphological method, individuals of the same species are combined according to similar shape and structure. By appearance black and white crow belong to different types.

Morphological characteristics are one of the main ones, but often not decisive. In nature there are collections of organisms that have common external features, but not interbreeding. They are sibling species.

An example is species of mosquitoes previously classified as malarial. They are distinguished by a dissimilar food base, which assigns individuals to different ecological niches.

Ecological criterion of the species

Involvement in the individual environment is fundamental principle ecological criterion.

One type of mosquito feeds on the blood of mammals, another on birds, and a third on reptiles. However, some insect communities serve as carriers of malaria, while others do not.

Accordingly, two different species cannot coexist within the same ecological niche, but different living organisms of the same species can live in dissimilar habitats. Groups of these homogeneous populations are called ecotypes.

Physiological (physiological-biochemical) criterion of the type

The physiological criterion is manifested in connection with the characteristics of the complex complex of vital functions of the organism and its individual systems. According to this classification, individuals are grouped together based on the similarity of their reproductive processes.

Organisms outside the same species are virtually incapable of interbreeding or produce infertile offspring. But there are individual representatives capable of reproduction and producing viable offspring.

Therefore, division into species based only on physiological characteristics is erroneous.

Geographic criterion of the species

The geographical criterion is based on identifying the distribution areas of individuals in certain territorial areas. But often the ranges of different species overlap or are disrupted, which calls into question the absolute application of the method.

Behavioral criterion of the species

The behavioral or ethological criterion characterizes interspecific differences in the behavior of individuals.

Bird songs or sounds made by insects are used to recognize certain types of animals. Important role plays behavior during mating, reproduction and the nature of caring for offspring.

Species criteria - table for biology lessons with examples

Morphological characteristics of representatives of flora and fauna

common wolf

The genus of wolves consists of seven species and 17 subspecies belonging to the common or gray wolf (Canis lupus). The division into subspecies groups occurred due to different body proportions and hair color.

Morphological characteristics:

• large sizes;
• external resemblance to a dog, differences in a more sloping frontal part, elongated paws, lowered rear part of the body, straight tail and special hair structure;
• dark gray stripe along the ridge, the crown of the head with dark markings, a characteristic “mask” on the muzzle;
• The color is gray-brown, ocher-rust and fawn, the roots and ends of the hair are dark, the middle is light in color.

The geography of its habitat differs in the breadth of its range. It exists in flocks of 2 to 40 animals. It is distinguished by highly social development. They make various sounds that facilitate communication between individuals.

Wolf refers to typical predators, but the diet also contains plant foods.

The wolf is a monogamous animal, living in pairs from mating until the offspring grow up. Mating games last from January to March. Sexual maturity in males occurs from 2 to 3 years, in females - by 2 years.

Cactus

The numerous cactus family has approximately 2800 species and is divided into 3 subfamilies:

1. Peiresquiaceae cacti include deciduous representatives;
2. Opuntiaceae consist of flat cacti and are divided according to shape into 3 groups;
3. Cereus includes plants lacking leaves and glochidia.

Distinctive morphological features:

• the presence of an areola, represented by spines or hairs;
• the unique structure of the fruit and flower, which is the tissue of the stem.

The habitat of cacti is North and South America.

Amur tiger

The Amur tiger differs from other tigers in geographical and morphological characteristics. Area – Far East And Northern part China.

TO external differences relate:

• thick and long fur;
• fewer stripes.

Which type criterion is the most accurate?

The clearest boundaries between species groups can be determined using the genetic method.

But in nature, complete genetic isolation cannot exist, therefore, to determine whether an organism belongs to a certain species category, it is necessary to use several different criteria.

The oldest species criterion

The oldest and most widespread method of describing new species is the morphological criterion, which systematizes individuals according to external similarity.

This method is also the least accurate due to the frequent significant difference organisms certain type and morphological similarity of different individuals.

Conclusion

Species criteria contribute to in-depth study, analysis and the most accurate systematization of organisms. There are more than a million described species on Earth and a large number of still unknown and unexplored.

The study of species characteristics contributes to the understanding of the process of evolution on Earth.

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 the species is defined 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 related species within the genus they 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, the first to give modern names and who described many types 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 were 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 a large area of ​​range and number of individuals, when there is geographic isolation within them or individuals have a wide ecological valence, the presence of individuals with different karyotypes is typical. 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 different populations 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 different classes and types, karyotypes with the same number of chromosomes may occur. 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 there is a match, compare them by appearance. If not a karyogram is presented, among the chromosomes middle length find the shortest and longest in both images, compare them by size and centromere location. 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. If the number of chromosomes is different, as well as the discrepancy between the characteristics of size and shape, 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.

View (lat. species) - a taxonomic, systematic unit, a group of individuals with common morphophysiological, biochemical and behavioral characteristics, capable of mutual crossing, producing fertile offspring in a number of generations, naturally distributed within a certain area and similarly changing under the influence of factors external environment. A species is a really existing genetically indivisible unit of the living world, the main structural unit in a 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 to both tigers and lions. Many other species are interbred in captivity, which natural conditions do not interbreed due to geographic or reproductive isolation. Crossing (hybridization) between different species can also occur in natural conditions, especially with anthropogenic disturbances of the habitat that disrupt ecological isolation mechanisms. Plants hybridize especially often in nature. A noticeable percentage of species higher plants has a hybridogenic origin - they were formed during hybridization as a result of partial or complete fusion of parent species.

Basic criteria of the type

1. Morphological criterion of the species. Based on existence morphological features, 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.
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. Based on what each species occupies certain territory(or water area) – geographical area. For example, in Europe, some species of 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.

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.

4. Molecular genetic criterion. Based on the degree of similarity and difference of nucleotide sequences in nucleic acids. Typically, “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 may have similar sequences.

5. Physiological-biochemical criterion. Based on the fact that different species may differ in the amino acid composition of proteins. At the same time, there is protein polymorphism within a species (for example, intraspecific variability of many enzymes), and different species may 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 durum wheat has 28 chromosomes in the diploid set, and all soft wheat has 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).

7. 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.

8. 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 types North American fireflies vary in the frequency and color of their 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 comparative analysis modern ranges of species (geographical criterion), comparative analysis of genomes (molecular genetic criterion), comparative analysis of cytogenomes (cytogenetic criterion) and others.

None of the considered species criteria is the main or most important. To clearly separate species, it is necessary to carefully study them 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 poorly differentiated internal structure, they are characteristic of endemics. Polytypic species are distinguished by a complex intraspecific structure.

Within species, subspecies can be distinguished - geographically or ecologically isolated parts of the species, individuals of which, under the influence of environmental factors in the process of evolution, acquired stable morphophysiological characteristics 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 it belongs this type, and the second word, called a species epithet in botany, and in zoology - species name. 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 the generic name, or a noun in genitive case. The first word is written with a capital letter, the second with a lowercase letter.

• Petasites fragrans - scientific name species of flowering plants from the genus Butterbur ( Petasites) (Russian name species - 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 - Butterbur Fomina). 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 unspecified taxa at species rank:

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

In the process of practical human activity the concept of the 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 the most important characteristics this unit. Thus, a species, according to Ray, is a set of organisms that are characterized by 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 writings the position that in the nature of unchangeable systematic units 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 conditioned historical development under the influence In accordance with Darwinian teachings, it was carried out comprehensive study systematic units. Thus, a study was carried out of the morphological criterion of the species, as well as experimental, genetic research 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 of the organic world as a whole.

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 species differs from another in its set 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 similar external and internal structure. The morphological criterion of the species is considered quite convenient and simple sign. 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 differences.