Kingdom (biology)
In the field of biology, a kingdom represents each of the large taxonomic subdivisions into which living beings are classified with respect to their evolutionary relationship. Kingdom is the second level of classification below domain and above phylum and, like the rest of the taxonomic groups, its spelling and pronunciation is Latin. Historically, the first kingdoms established to classify nature were animal, vegetable and mineral, but with the advent of biological study the system of the five kingdoms of life (Animalia, Plantae, Fungi, Protista and Monera) became popular.), classified more by their appearances than by their true evolutionary relationship.
However, the classification of the kingdoms is currently being redefined to better represent the phylogeny of each group. On the one hand, the kingdom Protista is a paraphyletic classification, where some of its phyla have as many differences between them as these with Animalia, Plantae or Fungi. For this reason, and to facilitate its study, it is increasingly common for Protista to be divided between the kingdoms Chromista and Protozoa.
On the other hand, Monera is a disused term that included two well-differentiated groups: the current domains Archaea and Bacteria where, in addition, Archaea would be slightly more related to Eukarya. This scheme was proposed by Woese in 1977 when he noted the great differences between archaea and bacteria at the ribosomal genetic level, despite the fact that both groups are composed of organisms with prokaryotic cells.
The kingdom taxonomic classification is not used for the cataloging of prokaryotes (Archaea and Bacteria), where only domain grouping is used. For this reason, at present, the kingdom system is restricted to eukaryotic organisms, that is, animals, plants, fungi, protozoa and algae.
 Archaea. |  Bacteria. |  Protozoa. |  Fungi. |  Chromist. | _version_2.png) Plant. |  Animalia. |
| Domains | Kingdoms | |
|---|---|---|
| Archaea | ||
| Bacteria | ||
| Eukarya | Protozoa (protozoa) | |
| Fungi (hongos) | ||
| Chromist (algae) | ||
| Plantae (plants) | ||
| Animalia (animals) | ||
History
Two Kingdoms System
Historically, the first organization into kingdoms is due to Aristotle (4th century BC), who differentiated all living entities of nature into two kingdoms: plant and animal. The first characterized by having "vegetative soul" that gives it reproduction, growth and nutrition. The second additionally has "sensitive soul" which gives it, in addition to the above, movement, perception and desire. Aristotle laid the foundations of systematic knowledge, as he divided the animal kingdom into two major genera: anaima for animals without blood (invertebrates) and enaima animals with blood (vertebrates).); and these in turn were divided into genera and species.
Carlos Linnaeus also distinguished these two kingdoms of living beings and also treated minerals, placing them in a third kingdom, Lapides. In addition, he introduced binomial nomenclature to refer to species and divided kingdoms into classes, classes into orders, orders into families, families into genera, and genera into species (the division of kingdoms into phyla was introduced later)..
Later, with the invention of microscopy, a new world of biological research appeared that would change the concept of kingdoms. A comparison of the most notable biological kingdom classification systems is presented in the following table:
| Linnaeus 1735 2 kingdoms | Haeckel 1866 3 kingdoms | Chatton 1925 2 groups | Copeland 1938 4 kingdoms | Whittaker 1969 5 kingdoms | Woese et al. 1977, 1990 3 domains | Cavalier-Smith 1998 6 kingdoms | Ruggiero et al. 2015 2 superrenants 7 kingdoms |
|---|---|---|---|---|---|---|---|
| (non-treated) | Protist | procariot | Monera | Monera | Archaea | Bacteria | Archaea |
| Bacteria | Bacteria | ||||||
| eucariot | Protoctist | Protist | Eucarya | Protozoa | Protozoa | ||
| Chromist | Chromist | ||||||
| Vegetabilia | Plane | Fungi | Fungi | Fungi | |||
| Plane | Plane | Plane | Plane | ||||
| Animalia | Animalia | Animalia | Animalia | Animalia | Animalia |
Three Kingdoms
In 1858, Richard Owen observed the difficulty of classifying microbial beings into animals and plants, for which he proposed creating the kingdom Protozoa and defined them as mostly tiny beings made up of nucleated cells.
In 1860 the English biologist John Hogg postulated the third Regnium primigenium or Protista for protozoa, protophytes and simple forms, such as the green freshwater sponge Spongilla which is actually a symbiote with green algae. Hogg actually spoke of four kingdoms: animal, plant, primal, and mineral. Hogg's ideas were overshadowed by Ernst Haeckel, who is considered the founder of protistology.
Haeckel in 1866 named the third kingdom Protista and defined it as the "primordial", the kingdom of primitive forms and intermediate between the Animal and Plantae kingdoms. He recognized that his classification was problematic due to the presence of animal, vegetable and mixed characters, but necessary for systematic, rather than phylogenetic, purposes. Within protista he placed the bacteria in the Moneres phylum. He was the first to distinguish between unicellular (protists) and multicellular (plants and animals) organisms. In subsequent publications, Haeckel made corrections to his classifications: for example, he moved sponges from the protista kingdom to animal, fungi from the plant kingdom to protista, blue-green algae from the plant kingdom to protista along with bacteria, Labyrinthulomycetes from animal to protista. and the volvocales from protista to plant.
Four Kingdoms
The concept of the third kingdom was questioned by Otto Bütschli in the 1880s, since Protista was considered polyphyletic, especially due to the inclusion of bacteria. Gradually the importance of the distinction between prokaryotes and eukaryotes proposed by Edouard Chatton from 1925-1937 became apparent and became popular in the 1950s.
Herbert Copeland in his 1938, 1947 and 1956 publications, separates nucleated protists from anucleated bacteria into the following four kingdom system: Plantae (or Metaphyta), Animalia (or Metazoa), Protista (or Protista) and Mychota (or Monera) for bacteria.
In 1948, the editors of Bergey's Manual of Determinative Bacteriology suggested naming the new kingdom Protophyta, to include both bacteria and viruses.
Five Kingdoms
Robert Whittaker recognized the additional kingdom of fungi (Fungi) in 1959. The result was the 5 kingdom system, proposed in 1969, which became a very popular standard and which, with some modifications, is still used today in many works or forms the basis for new proposed systems. It is mainly based on differences in nutrition: Plantae are mostly multicellular autotrophs, Animalia multicellular heterotrophs, and Fungi multicellular saprophytes. The other two kingdoms, Protista (eukaryotes) and Monera (prokaryotes), include single-celled or colonial organisms.
Confronting the possibility that some of these kingdoms might not be monophyletic, Whittaker argues: "Monophyly is a paramount value in systematics, but like other values, it is not absolute and is not always true. must follow if other targets are sacrificed".
Other works have supported this five-kingdom system, such as by Margulis (1974) and Margulis & Schwartz (1998), who used Hogg's original term Protist.
Multi-realm systems
Since Haeckel proposed the kingdom Protista, many biologists considered this group to be excessively polyphyletic or paraphyletic and should be subdivided into several monophyletic kingdoms. Hennig in 1950 proposed his theory of phylogenetic systematics (later called cladist), which explicitly introduced the concept of evolution in systematics by monophyletic groups (as Darwin postulated).
One of these systems was that of G. F. Leedale, who in 1974 proposed 19 kingdoms: Monera, Rhodophyta, Plantae, Heterokonta, Eustigmatophyta, Haptophyta, Cryptophyta, Dinophyta, Euglenophyta, Chytridiomycota, Fungi, Myxomycota, Zoomastigota (zooflagellates), Sarcodynia, Ciliophora, Sporozoa, Animalia, Porifera, and Mesozoa. However, many of these clades have been regrouped or superseded by continually updated protist phylogenetic study.
Other systems have been proposed. The largest is probably that of A.L. Drozdov (2003), who proposed 26 kingdoms.
Six Kingdoms
In the 1980s there was a breakthrough in prokaryotic phylogeny thanks to the advent of genetic analysis. On the basis of studies of rRNA (more specifically DNA encoding prokaryotic 16S and eukaryotic 18S ribosomal RNA), Carl Woese and G. Fox in 1977 divided the prokaryotes or Moneras into two superkingdoms: Eubacteria and Archaebacteria. In 1990, Woese renamed the new groups for which he postulated the three-domain system formed by Bacteria, Archaea and Eucarya. This system is currently the most accepted for the classification of living beings and is opposed to the two-empire system.
These two prokaryotic groups Archaea (or Archaebacteria) and Bacteria (or Eubacteria), are considered by other authors as kingdoms together with plants, animals, fungi and protists, which constitutes the system of six kingdoms, a system that has become standard in many educational works and books. The six kingdoms are attributed to Woese, but in reality by a tangential interpretation, since he actually spoke of three primary kingdoms or super-kingdoms (Woese 1977). Archaea and Bacteria are considered as domains or super-kingdoms but they are also treated as kingdoms, since they are always subdivided into phyla. The Archaebacteria and the Bacteria were previously classified as organisms of the Monera kingdom, but in the 70s and 80s a difference was found mainly in the structure of the cell wall and membranes, which caused the kingdom to be divided into 2 parts.
Realms have the following characteristics:
- Bacteria: are procariots that present a typical cellular wall of peptidoglycan, can be didérmicas (Gram negative) or monodermals (Gram positive). They are the most abundant beings, with a variety of habitats and metabolisms. There are several photosynthetic groups, but most are aerobics that feed on organic substances (chemium-organo-heterotrophos). They can be pathogens.
- Archaea: arches are procariot whose cell wall does not have peptidoglycan but glycoproteins or other compounds. They are monodermal because they have a single membrane. There are several hyperthermophile groups, thermoaccidophils, hypersalinians, and methanogens. Most of them are anaerobics with chemosynthetic metabolism (chemiolitoautropho) and are not pathogens.
- Protist: they are the simplest eukaryants, make up a group consisting of protozoos, algae and mucilaginous molds. They are a basal (paraphylical) group as they derive from the Plantae, Fungi and Animalia kingdoms. They are mostly unicellular, with the exception of mixedomicetes, pseudo-hongos and phenophic algae.
- Plane: are the oxygenic photosynthetic eukaryants, with chloroplasts that present chlorophyll a and b. They are mainly multicellular and descendants of Primoplantae, although the delimitation may vary according to the authors. Cellular walls and structural tissues contain cellulose. In reproduction is common haplo-diploid alternation. They highlight land plants.
- Fungi: they are heterotrophic eukaryants, aerobics and osmotrophos, mostly multicellular whose cell walls contain thyina. Reproduction is by haploid spores. The sapróphyte mushrooms stand out.
- Animalia: are heterotrophic eukaryants, aerobics, fagótrophos and multicellulars of great thysular differentiation. Their cells are diploids and haploid gametes. They present locomotive, embryonic development by blasting and structural protein is collagen. It is common a nervous system for the sensory and motor function of muscle contraction.
Seven Kingdoms
Since then, multitudes of new eukaryotic kingdoms have been proposed, but most were quickly invalidated, reclassified to phyla or class level, or abandoned. The only one that was still mentioned by some authors has been the system of six kingdoms of Cavalier-Smith, which proposes the Chromista kingdom to include organisms such as brown algae, yellow-green algae, golden algae, diatoms, oomycetes and other related ones.; and to the kingdom Protozoa (of the protozoa) as a basal eukaryotic group. This proposal has been gradually receiving attention, although the question of the relationships and division of living beings into groups is still a matter of discussion.
The most recent taxonomy (System of the Catalog of Life 2015), seeks to establish a manageable and practical classification, so that the evolutionary and phylogenetic criteria are relative, admitting some paraphyletic groups in certain cases. It collects part of the Cavalier-Smith postulates and presents the following classification into two super-kingdoms and seven kingdoms:
- I. Prokaryota
- 1. Archaea
- 2. Bacteria
- II. Eukaryota
- 3. Protozoa
- 4. Chromist
- 5. Fungi
- 6. Plane
- 7. Animalia
This system includes two new kingdoms, which can be described as follows:
- Protozoa: Paraphylical basal group with the most primitive eukaryotic characteristics. They are usually naked cells (without rigid cover), with mobility, flogged or with ameboid tendencies. Mostly they are unicellular, except for some groups of mucillaginous molds and almost all groups are heterotrophos feeding by fagocytosis.
- Chromist: Eukaryotic group philosophically close to Plantae and constituted by very diverse organisms, many of them photosynthetic (algae) containing chlorophyll a and c. Most are unicellular, except for pseudo-hongos and brown algae. They usually present stiffness due to the presence of cellular wall or some type of cover.
Other classification levels
Due to the high variety of life, numerous levels of classification called taxa have been established. The kingdom level was until recently the top level of biological classification. In modern classifications the top level is dominion, superkingdom, or empire; each of which is subdivided into kingdoms, the kingdoms, in turn, can be organized into phyla, etc. The most important levels of biological classification are shown below:
- Surrender, domain or empire (Superregnum, Dominium, Imperium).
- Kingdom (Regnum)
- Subrender (Subregnum)
- Rama (Ramus)
- Infrarreino (Infraregnum)
- Fill (animals and others) or Division (plants and fungi).
- Class
- Order
- Family
- Gender
- Species
- Gender
- Family
- Order
- Class
- Fill (animals and others) or Division (plants and fungi).