Biochemical criterion of a species: definition, examples. Characteristics of the type criteria Anatomical type criterion
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 combines similar morphological and physiological signs organisms. 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 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 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 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 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 morphological criterion kind is quite 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.
View - an elementary structural unit in the system of living organisms, a qualitative stage in their evolution. This is a collection of individuals that have similarities in internal and external structure, biochemical and physiological functions, freely interbreeding and producing fertile offspring, adapted to certain living conditions, having a certain type of relationship with abiotic (inert) and biotic environment and occupying a certain area in nature - habitat.
The species differ from each other in many ways. The characteristics and properties characteristic of a species are called criteria. As can be seen from the definition, among the criteria there are: morphological, physiological, cytogenetic, environmental and geographical .
Ecological criterion or environmental characteristics type is a combination of factors external environment, in which the species exists. The habitat is determined by a combination of factors (abiotic, biotic and anthropogenic) and elements affecting the species in its habitat.
Thanks to diversity environmental factors There is a natural distribution of species around the planet. Fluctuations in the intensity of environmental factors are manifested in the disappearance of some species from certain territories, changes in their density, fertility and mortality rates. Under the influence of environmental factors, such adaptive modifications as hibernation or summer hibernation, diapause.
Any individual or community experiences the simultaneous impact of many factors, but only some of them are vital - limiting . The absence of these factors or their concentration above or below critical levels makes it impossible for individuals of a certain species to master the environment.
Due to the presence of limiting environmental factors for everyone biological species There is an optimum and limits to endurance.
For example, oysters the best way develop in water with a salt concentration of 1.5 - 1.8%. When the salt concentration is reduced to 1.0%, more than 90% of the larvae die within two weeks, and at a concentration of 0.25%, the entire population dies in one week. Increasing the salt concentration above the optimum level also has an adverse effect on oysters.
The interrelationship of several environmental factors makes environmental conditions even more complex.
The ability of a species to master different environments habitat is expressed by the value of ecological valency, depending on which species are distinguished stenotopic or eurytopic .
Eurytopic species can be represented by several ecotypes - varieties adapted to survive in environments that differ in certain factors.
For example, the asteraceous plant yarrow forms lowland and mountain ecotypes; the same property is characteristic of many other plants, for example, St. John's wort.
Each individual of the species is associated with old and young generations, with predators or prey, food items, enters into competitive relationships with neighbors or is associated with mutual assistance. The existence of a species' range does not mean that all individuals of the species are able to move freely throughout its entire territory. The degree of mobility of individuals is expressed by the distance over which the animal can move or the distance over which the generative and vegetative parts of the plant can move and is called activity radius .
For example, for a snail it is several tens of meters, for a beaver - several hundred meters, for reindeer- several hundred meters.
As a result, organisms living in opposite parts of their range often have little chance of meeting, although their meeting and the likelihood of offspring still exist. This leads to the fact that individual individuals of a species, adapting to specific habitat conditions, are united into natural groups (aggregates) or populations.
For example, all the perches in a small lake or all the trees of the same species in a forest.
Until the end of the 18th century. There was a doctrine about monotypic form , i.e. it was believed that the species was homogeneous within itself. Currently, the generally accepted doctrine is polymorphic form , subdivided into subspecies within which populations are distinguished.
In biology, a species is a certain collection of individuals that have hereditary similarities in physiological, biological and morphological features, are able to interbreed freely and produce viable offspring. Species are stable genetic systems because in nature they are separated from each other by a certain number of barriers. Scientists distinguish them from each other according to a number of basic characteristics. Typically, the following criteria for a species are distinguished: morphological, geographical, environmental, genetic, physical and biochemical.
Morphological criterion
Such signs are the main ones in this system. Morphological criteria for a species are based on external differences between individual groups of animals or plants. This condition divides organisms into species that clearly differ from each other in internal or external morphological characteristics.
Geographic criteria of the species
Based on the fact that representatives of each stable genetic system live within limited spaces. Such zones are called habitats. At the same time geographical criterion has some shortcomings. It is not universal enough for the following reasons. First, there are some cosmopolitan species that are distributed throughout the planet (for example, the killer whale). Secondly, many biological populations have geographically identical habitats. Third, in the case of some overly rapidly expanding populations, the ranges are very variable (for example, the sparrow or the house fly).
Ecological criterion of the species
It is assumed that each species is characterized by certain characteristics, such as the type of food, timing of reproduction, habitat, and everything that determines the ecological niche it occupies. This criterion is based on the assumption that the behavior of some animals differs from the behavior of others.
Genetic criterion for the species
Here the main property of any species is taken into account - its genetic isolation from others. Plants and animals of different stable genetic systems almost never interbreed. Of course, a species cannot be completely isolated from the flow of genes from related species. However, at the same time, it generally maintains the constancy of its genetic composition over a truly long period of time. It is in the genetic component that the clearest differences between representatives of different biological populations lie.
Physico-biochemical criteria of the species
Such criteria also cannot serve as an absolutely reliable way to distinguish between species, since fundamental biochemical processes
occur in similar groups in the same way. And in the environment of each individual species there is a certain number of adaptations to certain living conditions, which affects changes in biochemical processes.
conclusions
Thus, it is very difficult to distinguish between species based on any single criterion. The belonging of an individual to any particular species should be determined only through a comprehensive comparison according to a number of criteria - all or at least the majority. Individuals that occupy a certain territory and are able to interbreed freely with each other are a species population.
INTRA-POPULATION STRUCTURE AND SPECIES CRITERIA
Species as a basic systematic unit
The entire diversity of the animal world, including the ichthyofauna, consists of species (Species), each of which is the main systematic unit. For the first time, with possible completeness, the genetic relationship of individual classes, orders and families of fish was shown by Academician L.S. Berg in 1916
According to L.S. Berg, a species is a set (community) of individuals occupying a geographic area characteristic of them, possessing certain morphological characteristics that are inherited and due to which this species differs from related species.
Species are continuously changing sets of individuals that have general properties in the structure, function (functions) of organs and lifestyle. Self-reproduction of their own kind, i.e. individuals possessing the same species characteristics and properties like the parents - this is the main characteristic property of the species. The self-reproduction of similar individuals can continue as long as the environment to which the species is adapted in the process of its formation will exist. All individuals of a species can interbreed and produce offspring. The species is characterized by relative morphological stability, which is the result of adaptation to the complex external conditions, under the influence of which it is formed and lives.
The structure of individuals of a species and their morphological characteristics is not a conglomerate of random properties, but an interconnected one system, which applies to both physiological and environmental characteristics. Each trait is associated with a specific function that can change during ontogenesis. If in a free embryo (pre-larvae of many cyprinids) the fin fold serves as a respiratory organ, then with the transition to a larval way of life unpaired fins turn into organs of movement.
Variability within a species does not go beyond the boundaries of morphological specificity. The species occupies a certain area (area) and is relatively stable over time. Once it has arisen, it quite stably retains its species properties and characteristics throughout history.
Type criteria
Morphological criterion
The morphological criterion includes characteristics of the structure of organs and tissues of the species. To characterize species, traits that reflect adaptations to environmental conditions can be successfully used. For example, the most clear morphological differences in different types whitefish in the structure and position of the mouth, the number of gill rakers are associated with differences in the nature of nutrition. In many species, the most obvious differences are observed in characters related to the nature, places and timing of reproduction (for example, Far Eastern salmon of the genus Oncorhynchus).
Characterizing individual species, it is necessary to use not only signs associated with feeding habits (structure and position of the mouth, lower pharyngeal teeth, character intestinal tract etc.), but also signs associated with movement (for example, the number of scales in the lateral line) and with the structure of the fins - their shape, the number of rays. Besides, great importance have anatomical characteristics; the structure of the skull (herring, cod, salmon), the structure of the vertebral bodies (cod), the number of pyloric appendages (mullet), etc. The morphological characteristics also include the nature of the karyotype: the number of chromosomes, the size of the chromosomes and other features of their structure.
Morphological criterion reflects the external and internal similarity of individuals of the same species.
Yes, black and white crow 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. So, in Drosophila, 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, for a long time this criterion was considered the main and only one when determining species (Fig. 39).
At the core physiological criterion lies the similarity of life processes in individuals of each species, especially reproduction.
Representatives various types 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 twin species of the black rat has 38, the other 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.