In biology, a species is the basic unit of taxonomic classification and rank, as well as the biodiversity unit, but has proven difficult to find a satisfactory definition. Scientists and conservationists need a species definition that allows them to work, regardless of their theoretical difficulties. If as Linnaeus thinks, the species is improved, there will be no problem, but the process of evolution causes the species to change constantly, and to judge one another. A species is often defined as the largest group of organisms in which two individuals can produce fertile offspring, usually through sexual reproduction. Although this definition is often adequate, when viewed more closely, it is problematic. For example, by hybridization, in a species complex of the same hundreds of microspecies, or in a ring species, the boundaries between closely related species become unclear. Among the organisms that reproduce only asexually, the concept of reproductive species is damaged, and each clone has the potential to become microspecies. Problems also arise when dealing with fossils, because reproduction can not be examined; the concept of chronospecies is therefore used in paleontology. Other ways to define species include their karyotype, DNA sequence, morphology, behavior or ecological niche.
All species are named two parts, "binomial". The first part of the binomial is the genus that belongs to the species. The second part is called a specific name or nickname (in botanical nomenclature, also sometimes in zoological nomenclature). For example, Boa constrictor is one of four species of the genus Boa .
Species seen from the time of Aristotle until the 18th century as a fixed type that can be set in the hierarchy, the chain of existence is great. In the 19th century, biologists understood that species can evolve with sufficient time. The book of Charles Darwin in 1859 The Origin of Species describes how species can arise through natural selection. This understanding was greatly expanded in the 20th century through the genetics and ecology of the population. Genetic variability arises from mutation and recombination, while the organism itself moves, leading to geographical isolation and genetic drift with various selection pressures. Genes can sometimes be exchanged between species with horizontal gene transfer; new species can emerge rapidly through hybridization and polyploidy; and species may become extinct for a variety of reasons. Viruses are a special case, driven by a balance of mutations and selection, and can be treated as quasispecies.
As a practical matter, the concept of species can be used to define species that are then used to measure biodiversity, although whether this is a good debatable measure, as other measures may be.
Video Species
History
Classic shapes
In biology, Aristotle uses the term ????? (gÃÆ' Â © nos) means a kind, like a bird or a fish, and ????? (eidos) means specific forms of a kind, such as (in birds) cranes, hawks, crows, or sparrows. These terms are translated into Latin as "genus" and "species", although they are inconsistent with the term Linnean so named; today the bird is the class, the heron is the family, and the genus crow. Such is distinguished by its attributes; for example, birds have feathers, beaks, wings, hard shell eggs, and warm blood. A form is distinguished by the sharing of all its members, the young inheriting whatever variations they may have from their parents. Aristotle believed all types and forms to be different and unchanged. His approach remained in fl uence until the Renaissance.
Species remain
When observers in the Early Modern period began to develop organizational systems for living things, they placed every type of animal or plant into a context. Many of these early depiction schemes will now be considered odd: schemes including color-based neighborhoods (all plants with yellow flowers) or behavior (snakes, scorpions and certain bite ants). John Ray, a British naturalist, was the first to attempt a species biological definition in 1686, as follows:
There is no more definite criterion for determining which species have occurred to me than the discriminating characteristics that perpetuate themselves in the multiplication of seeds. Thus, no matter what variations occur to individuals or species, if they arise from the same seeds and plants, they are accidental variations and unlike to distinguish species... Different animals specifically defend their differences. species permanently; one species never arises from another seed or vice versa.
In the 18th century, Swedish scientist Carl Linnaeus classified organisms based on shared physical characteristics, and not just on the basis of differences. He sets the idea of ​​a classification of taxonomic hierarchies based on observable characteristics and is intended to reflect the nature of relationships. At that time, however, it is still widely believed that there is no organic relationship between species, no matter how similar they appear. This view is influenced by European academic and religious education, which states that the category of life dictated by God, constitutes the Aristotelian hierarchy, scala naturae or a large chain of existence. However, whether or not it should be fixed, scala (ladder) inherently implies the possibility of climbing.
Possible changes
Faced with evidence of hybridization, Linnaeus accepts that species may change, and struggle for survival, but not a new species that can evolve freely. In the 19th century, naturalists understand that species may change over time, and that planetary history provides enough time for major change. Jean-Baptiste Lamarck, in 1809 Zoological Philosophy , describes the transmutation of species, proposing that a species may change from time to time, in the radical departure of Aristotelian thought.
In 1859, Charles Darwin and Alfred Russel Wallace gave convincing reports about the evolution and formation of new species. Darwin argues that it is an evolving population, not an individual, by natural selection of naturally occurring variations among individuals. This requires the definition of a new species. Darwin concludes that species are what they seem to be: ideas, while useful for naming groups of interacting individuals, writes:
I see the term species as an arbitrary one given for ease to a set of individuals very similar to each other... This is basically no different from the word variety, which is given to a less distinct and fluctuating form. The variety of terms, again, compared to individual differences, is also applied arbitrarily, and for convenience.
Maps Species
Taxonomy and naming
Common and scientific names
The names commonly used for this type of organism are often ambiguous: "cat" can mean domestic cat, Felis catus , or cat family, Felidae. Another problem with common names is that they often vary from one place to another, so puma, cougar, catamount, panther, painters and mountain lions all mean Puma concolor in various parts of America, while "panther" can also mean jaguar ( Panthera onca ) from Latin America or the leopard (Panthera pardus ) of Africa and Asia. Instead, the scientific names of species are chosen to be unique and universal; they are in two shared parts: the genus as in Puma , and the specific nickname as in concolor .
Description of species
A species is given a taxonomic name when a specimen type is formally described, in a publication that assigns it a unique scientific name. This description usually provides a means of identifying new species, distinguish them from other previously described species and related or confusing species and provide a valid published name (in botanical) or an available name (in zoology) when the paper is accepted for publication. This type of material is usually stored in permanent storage, often a collection of research from museums or major universities, allowing independent verification and means to compare specimens. The depiction of new species is asked to choose a name which, in the words of the International Code of Zoological Nomenclature, is "precise, compact, melodious, memorable, and non-infringing".
Abbreviation
Books and articles sometimes deliberately do not identify species completely and use the abbreviation "sp." in the singular or "spp." (Stand for Identification code
With the advent of online databases, codes have been designed to provide identifiers for defined species, including:
- The National Biotechnology Information Center (NCBI) uses a 'numerical taxid' or Taxonomic identifier , a "stable unique identifier", for example, a taxid of Homo sapiens 9606.
- The Kyoto Encyclopedia of Genes and Genomes (KEGG) uses three or four letter codes for a limited number of organisms; in this code, for example, H. sapiens is just hsa .
- UniProt uses "mnemonic organisms" that are no more than five alphanumeric characters, for example, HUMAN for H. sapiens .
- Integrated Taxonomy Information System (ITIS) provides a unique number for each species. LSID for Homo sapiens is a jar: lsid: catalogueoflife.org: taxon: 4da6736d-d35f-11e6-9d3f-bc764e092680: col20170225.
Lumping and splitting
The naming of a particular species, including the genus (and higher taxa) placed therein, is the hypothesis about the relationship of evolution and the ability to distinguish the group of organisms. When more information comes, the hypothesis can be confirmed or denied. Sometimes, especially in the past when communication was more difficult, taxonomists working separately had given two different names to individual organisms that were later identified as the same species. When two named species are found to be the same species, the name of the older species is given priority and is usually maintained, and the newer name is considered a junior synonym, a process called synonymous . Dividing the taxon into several, often new, taxa called separating . Taxonomists are often referred to as "lumpers" or "splitters" by their peers, depending on their personal approach to recognizing differences or similarities between organisms.
Wide and narrow senses
Nomenclature codes that guide species naming, including ICZN for animals and ICN for plants, do not make rules for defining species boundaries. Research can change boundaries, also known as limits, based on new evidence. Species then need to be distinguished by the definition of boundaries used, and in such cases names may be eligible with sensu stricto ("in the narrow sense") to indicate use in the exact sense given by authors such as people who name the species, while the antonym sensu lato ("in the broad sense") indicates wider usage, for example including other subspecies. Other abbreviations such as "auct." ("author") and "no." ("No") may be used to further clarify the notion in which the prescribed author describes or describes the species.
Konsep spesies biologis Mayr
Most modern textbooks use the 1942 definition of Ernst Mayr, known as the Biological Species Concept as the basis for further discussion of the definition of species. This is also called the concept of reproduction or isolation. It defines the species as
groups of natural populations of actual or potential reproduction, which are reproductively isolated from other such groups.
It has been argued that this definition is a natural consequence of the effects of sexual reproduction on the dynamics of natural selection. The use of the "potentially" adjective by Mayr has become a point of debate; some interpretations exclude unusual or artificial marriages that only occur in captivity, or that involve animals that are capable of mating but who usually do not do so in the wild.
The species issue
It is difficult to define a species in a way that applies to all organisms. The debate about species delimitation is called the species problem. The problem was recognized even in 1859, when Darwin wrote in On the Origin of Species :
There is no definition that satisfies all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species. Generally this term includes an unknown element of a different act of creation.
When the Mayr concept is corrupted
The definition of a simple textbook, following Mayr's concept, works well for most of the many celled organisms, but is damaged in some situations:
- When an organism reproduces asexually, as in single-celled organisms such as bacteria and other prokaryotes, and many cellular organisms are progenogenetic or apomictive. The term quasispecies is sometimes used to rapidly mutate entities such as viruses.
- When scientists do not know whether two groups of organisms that are similarly morphologically capable of interbreeding; this is the case with all life forms that have become extinct in paleontology, because breeding experiments are impossible.
- When hybridization allows a substantial flow of genes between species.
- In ring species, when members of adjacent populations within a wide range of sustainable distributions are successfully married but further members of the population do not.
Identification of species is made difficult by the clumsiness between molecular and morphological investigations; these can be categorized as two types: (i) one morphology, several lineages (eg morphological convergence, cryptic species) and (ii) one lineage, multiple morphology (eg phenotypic plasticity, multiple life cycle stages). In addition, horizontal gene transfer (HGT) makes it difficult to define a species. All species definitions assume that an organism obtains its genes from one or two parents is very similar to a "princess" organism, but that is not what happens in HGT. There is strong evidence of HGT between very different prokaryotic groups, and at least occasionally between different eukaryotic groups, including some crustaceans and echinoderms.
Evolutionary biologist James Mallet sums it up
there is no easy way to know whether the associated geographical or temporal forms belong to the same or different species. The species gap can be verified only locally and at some point in time. One is forced to admit that Darwin's insight is true: every local reality or species integrity is greatly reduced in the geographic span and large periods of time.
Aggregate microspecies
The concept of species is further undermined by the existence of microspecties, groups of organisms, including many plants, with very little genetic variability, usually forming species aggregates. For example, dandelion Taraxacum officinale and blackberry Rubus fruticosus is an aggregate with many microspesies - perhaps 400 in the case of blackberries and over 200 in dandelion, complicated by hybridization, apomixis and polyploidy, making gene flow between populations is difficult to determine, and their taxonomies are debatable. Complex species occur in insects such as butterflies Heliconius , vertebrates like Hypsiboas treefrogs, and mushrooms such as the agaric fly.
Hybridization
Natural hybridization presents a challenge to the concept of isolated reproductive species, as fertile hybrids allow the flow of genes between two populations. For example, crows of corvus corona and corvus cornix crows appear and are classified as separate species, but they are hybridized freely where their geographical range overlaps.
- Hybridization of hooded carcasses and crows allows gene flow between 'species'
Ringing type
Ring species are a series of interconnected neighboring populations, each capable of sexually crossbreeding with adjacent adjacent populations, but for the least two "end" populations in the series, which are too far linked to crossbreeding, potential genes between each "related" population. Non-breeding "end" populations, although genetically connected, can coexist in the same region to close the circle. Ring species thus present difficulties for any species concept that relies on reproductive isolation. However, the ring species most rarely. The proposed examples include dark gull complexes supported by the gull-less herring maggots around the North Pole, the Ensatina eschscholtzii group of 19 population salamanders in America, and the greenish warbler in Asia, but many so-called species rings have changed became the result of misclassification causing the question of whether there really is a ring species.
Trying on definition
Biologists and taxonomists have made great efforts to define species, ranging from morphology and moving toward genetics. Early taxonomists such as Linnaeus had no choice but to describe what they saw: it was then formalized as a typological or morphological species concept. Mayr emphasizes reproductive isolation, but this, like the concept of other species, is difficult or even impossible to test. Later, biologists try to improve Mayr's definition with the concept of recognition and cohesion, among others. Many concepts are very similar or overlapping, so they are not easily calculated: the biologist RL Mayden recorded about 24 concepts, and the philosopher John Wilkins counted 26. Wilkins further classifies the concepts of species into seven basic types of concepts: (1) agamospecies for asexual organisms (2) biospesies for isolated sexual reproductive organisms (3) ecospecies based on ecological niche (4) species evolution based on lineage (5) genetic species based on pool genes (6) morphospecies by shape or phenotype and (7) taxonomic species, species determined by taxonomists.
Species typology or morphology
Typical species are a group of organisms in which individuals correspond to certain fixed properties (types), so even pre-literate people often recognize the same taxon as the modern taxonomist. A collection of variations or phenotypes in a specimen (such as a longer or shorter tail) will distinguish the species. This method is used as a "classical" method for determining species, such as with Linnaeus at the beginning of the theory of evolution. However, different phenotypes are not necessarily distinct species (for example, four winged Drosophila born to two-winged mothers are not distinct species). Species that are named are called morphospesies .
In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed variations on this, phenetic species, defined as a collection of organisms with the same phenotype of each other, but a different phenotype than other sets of organisms. This differs from the concept of morphological species including the numerical distance of distance or similarity to cluster entities based on multivariate comparisons of a large number of phenotypic properties.
Introduction and cohesion species
The species that recognizes mate is a group of sexually reproducing organisms that recognize each other as potential partners. Extending this to enable post-mating isolation, the species of cohesion is the most inclusive population of individuals who have the potential for phenotypic cohesion through intrinsic cohesion mechanisms; regardless of whether the population can hybridize successfully, they are still different species of cohesion if the amount of hybridization is not sufficient to completely mix their respective genes. Further development of the concept of recognition is provided by the species biosemiotic concept.
Kesamaan genetik dan spesies barcode
In microbiology, genes can move freely even among adjacent bacteria, possibly extending to the entire bacterial domain. As a rule of thumb, microbiologists assume that the type of Bacteria or Archaea with a sequence of 16S RNA ribosome gene that is more similar than 97% to each other needs to be checked by DNA-DNA hybridization to decide whether they belong to the same species or not. This concept narrowed in 2006 to a similarity of 98.7%.
DNA-DNA hybridization is outdated, and results sometimes lead to misleading conclusions about species, such as with pomarines and large skua. The modern approach compares the sequence similarities using computational methods.
DNA barcoding has been suggested as a way to distinguish species that are suitable even for non-specialists to use. The so-called barcode is the region of mitochondrial DNA in the gene for cytochrome c oxidase. The Database, Barcode of Life Data Systems (BOLD) contains DNA barcode sequences from over 190,000 species. However, scientists such as Rob DeSalle have expressed concern that classical taxonomies and DNA barcodes, which they consider to be incorrect names, need to be reconciled, because they limit species differently. Genetic introgression mediated by endosymbionts and other vectors may further render barcodes ineffective in species identification.
Phylogenetic, cladistic, atau evolusioner species
Phylogenetic or clanistic species are distinct evolutionary genealogies, which have retained the integrity of heredity through time and space. The clanistic species is the smallest population group that can be distinguished by a unique set of morphological or genetic traits. Molecular markers can be used to determine the genetic similarity in nuclear DNA or mitochondria of various species. For example, in a study conducted on fungi, studying the character of nucleotides using cladistic species produced the most accurate results in recognizing various species of fungi from all learned concepts. Concept versions of Phylogenetic Species may emphasize monophyly or diagnosability.
Unlike the Biological Species Concept, cladistic species do not depend on reproductive isolation, so it does not depend on integral processes in other concepts. It works for asexual lineages, and can detect recent divergences, which can not be found by the Concept of Specific Morphology. However, it does not work in every situation, and may require more than one polymorphic locus to provide accurate results. This concept can lead to splitting existing species, such as Bovidae, into many new species.
The evolutionary species, advocated by George Gaylord Simpson in 1951, is "an entity composed of organisms that retain its identity from other entities such as through time and space, and which have the fate of independent evolution and historical trends" themselves. This differs from the concept of biological species in realizing persistence over time. Wiley and Mayden claim that they see the concept of evolutionary species as "identical" to the concept of Willi Hennig's species-as-line, and assert that the concept of biological species, "several versions" of the concept of phylogenetic species, and the idea that species are of the same kind with higher taxa not suitable for biodiversity studies (with the aim of accurately estimating species counts). They further suggested that this concept works for both asexual and sexual reproductive species.
Ecological species
Ecological species are a set of organisms adapted to a set of specific resources, called niches, in the environment. According to this concept, the population forms a discrete phenetic group that we recognize as species because of the ecological and evolutionary processes that control how the shared resources tend to produce the group.
Genetic Species
The genetic species as defined by Robert Baker and Robert Bradley is a set of genetically isolated marital populations. This is similar to the Mayr Biological Species Concept, but emphasizes genetic isolation rather than reproduction. In the 21st century, genetic species can be formed by comparing DNA sequences, but other methods are available earlier, such as comparing the karyotype (set of chromosomes) and allozymes (enzyme variants).
Significant evolutionary units
Evolutionarily significant units (ESU) or "wildlife species" are populations of organisms considered to be different for conservation purposes.
Chronospecies
In paleontology, with only the comparative anatomy (morphology) of fossils as evidence, the concept of chronospecies can be applied. During anagenesis (evolution, not always involving branching), palaeontologists attempt to identify the sequence of species, each coming from extinct before through continuous, slow and more or less uniform change. In such a time sequence, palaeontologists assess how much of a change is required for different morphological forms to be regarded as distinct species from their ancestors.
Viral quasispecies
Viruses have enormous populations, which are doubtful alive because they are composed of little more than strings of DNA or RNA in the protein layer, and mutate rapidly. All these factors make the concept of conventional species very invalid. A quasispecies virus is a group of genotypes associated with a similar mutation, competing in a high mutagenic environment, and hence governed by a selection-mutation balance. It is thought that virus quasispecies in low areas but neutral and highly connected evolution (ie, flat) in the fitness landscape will defeat quasispecies located at the height of higher but narrower fitness where the surrounding mutants are not feasible, "quasispecies effect" or "survival of the flattest ". There is no suggestion that virus quasispecies resemble traditional biological species.
Change
Species may change, whether by evolving into new species, exchanging genes with other species, joining other species or becoming extinct.
Speciation
The evolutionary process in which biological populations evolve into different or reproductively isolated species is called speciation. Charles Darwin was the first to describe the role of natural selection in speciation in his book 1859 The Origin of Species . The specification depends on the size of the reproductive isolation, the decreased gene flow. This happens most easily in alopathic speciation, where the population is geographically separated and can deviate gradually as mutations accumulate. The reproductive isolation is threatened by hybridization, but this can be selected against a pair of populations that have incompatible alleles of the same genes, as described in the Bateson-Dobzhansky-Muller model. Different mechanisms, phyletic speciation, involving one lineage gradually change over time into new and different forms, without increasing the number of species produced.
Gene exchange between species
Horizontal gene transfer between different species organisms, either through hybridization, antigenic shift, or reassortment, is sometimes an important source of genetic variation. Viruses can transfer genes between species. Bacteria can exchange plasmids with bacteria from other species, including some species that appear to be much different in different phylogenetic domains, make analyzing their relationships difficult, and weaken the concept of bacterial species.
Louis-Marie Bobay and Howard Ochman suggest, based on the genome analysis of many types of bacteria, that they can often be grouped "into communities that regularly exchange genes", in much the same way as plants and animals can be grouped into reproductive. isolated breeding populations. The bacteria can thus form a species, analogous to the concept of Mayr's biological species, composed of sexually reproducing populations that exchange genes with homologous recombination.
Extinction
A species is extinct when the last individual of the species dies, but may be functionally extinct before that time. It is estimated that more than 99 percent of all species that once lived on Earth, about five billion species, are now extinct. Some of them are in mass extinctions such as those at the end of the Permian, Triassic and Cretaceous periods. Mass extinctions have a variety of causes including volcanic activity, climate change, and changes in ocean and atmospheric chemistry, and they in turn have a profound effect on Earth's ecology, atmosphere, soil surface, and waters. Another form of extinction is through the assimilation of one species with another species through hybridization. The resulting single species have been referred to as "compilospecies".
Practical implications
Biologists and conservationists need to categorize and identify organisms in the course of their work. The difficulty of assigning organisms reliably to a species poses a threat to the validity of the research results, for example making measurements about how many species in the ecosystem are contested. Paul Michael-Agapow and colleagues found that surveys using the concept of phylogenetic species reported 48% more species and populations and smaller ranges compared to those using nonphylogenetic concepts; they noted that this "taxonomic taxonomy" could lead to a false change in the number of endangered species and the resulting political and practical difficulties. Evolutionary biologist Jody Hey observes that there is an inherent conflict between the desire to understand the speciation process and the need to identify and categorize. Conservation laws in many countries make specific provisions to prevent species becoming extinct. The hybridization zone between two species, one protected and one that does not, sometimes causes conflict between lawmakers, landowners and conservationists. One classic case in North America is a protected owl in the north that blooms a hybrid with an unprotected Californian owl and a forbidden owl; this has led to a legal debate.
The botanist Brent D. Mishler states that the species problem is created by the many ways that people want to use the species category, but argue that the solution is to leave the traditional ranks and only use the monophyletic groups of different inclusions. A species is then "only the most inclusive taxon" of any kind. He argues that ecology, evolution, and conservation work are all better served by this approach. Because in his view the species is not comparable, calculating it is not a valid measure for biodiversity, and he asked for a new way of measuring it, noting that other authors such as RI Vane-Wright and colleagues have proposed quantitative measures for phylogenetic biodiversity that make use of " branch point, and possibly branch length, separating the tip on the tree ".
See also
Note
Source cited
- Claridge, M. F.; Dawah, H. A.; Wilson, M. R., eds. (1997). Species. Unit of biodiversity . Chapman & amp; Hall.
- Wheeler, Quentin; Meier, Rudolf, eds. (2000). The concept of species and phylogenetic theory: the debate . New York: Columbia University Press. ISBN 978-0-231-10143-1.
- Zachos, Frank E. (2016). The concept of species in biology. Historical Developments, Theoretical Bases and Practical Relevance . Springer International Publishing.
External links
- Species (journals)
- Barcoding species
- Catalog of Life
- Name of European Species in Linnaean, Czech, English, German, and French
- Stanford Encyclopedia of Philosophy entry: Species
- VisualTaxa
- Wikispecies - The free species directory that anyone can edit from the Wikimedia Foundation
Source of the article : Wikipedia
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