Biochemical criterion of a species: definition, examples. The geographical criterion of a species is its Reproductive criterion of a species is not applicable to species that

Goals and objectives of the lesson: to form the concepts of “species”, “species criteria”, “population”; continue to develop skills in working with texts and tables; ability to analyze and draw conclusions.

During the classes

1. Organizational moment

Formulating the topic of the lesson. Setting lesson goals and objectives

2. Repetition of the material covered (establishing connections between previously studied material and the material of the new topic)

a) The concept of species by K. Linnaeus, J.B. Lamarck and C. Darwin (checking the correctness of answers on slides 2-4)

b) Who proposed the binary nomenclature for species?

c) What does a double title include? Give examples

Find in the textbook modern definition type (for checking step 5)

Why do you think the modern species definition is so difficult?

(avoid mistakes when determining whether individuals belong to the same species)

Teacher's addition: Linnaeus made a mistake in classifying the male and female mallard duck as different species, taking into account only external signs(sl. 6)

3.Learning new material

a) The teacher’s story about what a species is and what the criteria for a species are using a presentation; the concept of reproductive isolation, its causes and significance for the existence of the species is given (sl. 7-22)

Class assignment:

As you explain and view the video, fill in the resulting table

b) Watching a video fragment from the educational film “Type Criteria”, which provides specific examples of type criteria and their relativity.

V) Independent work students to make additions to the table after watching a video clip

d) Checking the basic concepts included in the table

e) Formulation of conclusions (sl. 23, 25)

4. Fastening (sl. 24-26)

5. The concept of “Population” (sl. 28-31)

6. Summing up the lesson, grading.

7. Homework: par 1.4.1, questions 1-5, table,

Additional questions for homework.

1. Two cultivated plants, barley and rye, have the same set of chromosomes (14), but do not cross, they differ in appearance and chemical composition. Determine: a) Barley and rye should be classified as the same or different species. b) What criteria specified in the text should be followed?

2. Two breeds of rabbits have the same number of chromosomes (44), but do not interbreed. differ in appearance and timing of puberty. a) Should these breeds of rabbits be classified as the same or different species? b) What criteria specified in the text should be followed?

References.

1. Textbook "Biology" V.B. Zakharov, S.G. Mamontov, V.I. Sivoglazov 11th grade.
2. G.M. Murtazin "Tasks and exercises in general biology"
3. N.A. Lemez, L.V. Kamnyuk, N.D. Lisov "A manual on biology for applicants to universities"
4. Magazine "Courier Unesco" June 1982
5. Internet Photos

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 area is geographical boundaries distribution of a species in which the size, shape and location are 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 are a large number of 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 a certain territory and freely interbreeding with each other 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 and 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.

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 mechanisms isolation. 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. It is based on the fact that each species occupies a certain territory (or water area) - a geographic range. 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 Oh. 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 in nature it is often common interspecific hybridization: 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 species of 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 the species belongs, and a 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 the generic name, or a noun in the genitive case. The first word is written with a capital letter, the second with a lowercase letter.

• Petasites fragrans- scientific name of a 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).

The qualitative stage of the evolutionary process is species. A species is a collection of individuals that are similar in morphophysiological characteristics, are capable of interbreeding, producing fertile offspring, and forming a system of populations that form a common habitat.

Each type of living organism can be described based on the totality characteristic features, properties, which are called features. Characteristics of a species by which one species is distinguished from another are called species criteria. The most commonly used are six general species criteria: morphological, physiological, geographical, environmental, genetic and biochemical.

The morphological criterion involves a description of the external (morphological) characteristics of the individuals included in the certain type. By appearance, size and color of plumage, you can, for example, easily distinguish a Great Spotted Woodpecker from a Green Woodpecker, a Lesser Spotted Woodpecker from a Yellow Woodpecker, big tit from the tufted, long-tailed, blue and from the chickadee. Based on the appearance of the shoots and inflorescences, the size and arrangement of the leaves, the types of clover can be 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 accumulated indicating 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. Thus, 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 to the west of India, and rats with 42 chromosomes, distribution which are associated with the Mongoloid sedentary civilizations inhabiting Asia east of Burma. It has also been established that under the name “malaria 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. Physiological isolation exists between different species. For example, in many species of Drosophila, the sperm of individuals of a foreign species causes an immunological reaction in the female genital tract, which leads to the death of sperm. At the same time, crossing is possible between some species of living organisms; in this case, fertile hybrids can be formed (finches, canaries, crows, hares, poplars, willows, etc.).

The geographical criterion (geographical specificity 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 area. Many species occupy different habitats. But a huge number of species have overlapping or overlapping ranges. In addition, there are species that do not have clear boundaries of distribution, as well as cosmopolitan species that live over vast areas of land or ocean. Some inhabitants of inland water bodies - rivers and freshwater lakes (species of pondweed, duckweed, reed) are cosmopolitans. An extensive set of cosmopolitans is found among weeds and garbage plants, synanthropic animals (species that live near humans or their homes) - bedbug, red cockroach, housefly, as well as dandelion, field grass, shepherd's purse, etc.

There are also species that have a discontinuous range. For example, linden grows in Europe and is found in the Kuznetsk Alatau and Krasnoyarsk Territory. The blue magpie has two parts of its range - Western European and Eastern 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 in certain conditions, performing a corresponding function in a certain biogeocenosis. In other words, each species occupies a specific ecological niche. For example, acrid buttercup grows in floodplain meadows, creeping buttercup grows along the banks of rivers and ditches, and burning buttercup grows in wetlands. There are, however, species that do not have a strict ecological association. Firstly, 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. by the 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, many different species have the same number of chromosomes and their shape is similar. Thus, many species from the legume family have 22 chromosomes (2n=22). Secondly, within the same species there may be individuals with different numbers chromosomes, which is the result of genomic mutations. For example, goat willow has a diploid (38) and tetraploid (76) number of chromosomes. In silver crucian carp, there are populations with a set of chromosomes of 100, 150,200, while the normal number is 50. Thus, in the case of the occurrence of polyploid or aneushyoid (the absence of one chromosome or the appearance of an extra one in the genome) forms, based on genetic criteria, it is impossible to reliably determine whether individuals belong to specific type.

The biochemical criterion allows you to distinguish between species according to biochemical parameters (composition and structure of certain proteins, nucleic acids and other substances). It is known that the synthesis of certain high-molecular substances is characteristic only of certain groups of species. For example, plant species differ in their ability to form and accumulate alkaloids within the families Solanaceae, Asteraceae, Liliaceae, and Orchids. Or, for example, for two species of butterflies from the genus Amata, a diagnostic sign is the presence of two enzymes - phosphoglucomutase and esterase-5. However, this criterion does not find wide application- it is labor-intensive and far from universal. There is significant intraspecific variability in almost all biochemical parameters, down to the sequence of amino acids in protein molecules and nucleotides in individual sections of DNA.

Thus, none of the criteria alone can serve to determine the species. A species can only be characterized by their totality.