Methods | Statistics | Clinical | Educational | Industrial | Professional items | World psychology |
In biology, a type is one particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralize the defining features of that particular taxon.
A taxon is a scientifically named grouping of organisms with other like organisms, a set that includes some organisms and excludes others, based on a detailed published description (for example a species description) and on the provision of type material, which is usually available to scientists for examination in a major museum research collection, or similar institution.
According to a precise set of rules laid down by the ICZN and the ICBN, the scientific name of every taxon is almost always based on one particular specimen, or in some cases specimens. Types are of great significance to biologists, especially to taxonomists. Types are usually physical specimens that are kept in a museum or herbarium research collection, but failing that, an image of an individual of that taxon has sometimes been designated as a type. Describing species and appointing type specimens is part of scientific nomenclature and alpha taxonomy.
When identifying material, a scientist attempts to apply a taxon name to a specimen or group of specimens based on his or her understanding of the relevant taxa, based on (at least) having read the type description(s), preferably based on an examination of all the type material of all of the relevant taxa. If there is more than one named type that all appear to be the same taxon, then the oldest name takes precedence, and is considered to be the correct name of the material in hand. If on the other hand the taxon appears never to have been named at all, then the scientist or another qualified expert picks a type specimen and publishes a new name and an official description.This process is crucial to the science of biological taxonomy. People's ideas of how living things should be grouped change and shift over time. How do we know that what we call "Canis lupus" is the same thing, or approximately the same thing, as what they will be calling "Canis lupus" in 200 years time? It is possible to check this because there is a particular wolf specimen preserved in a museum somewhere, and everyone who uses that name – no matter what else they may mean by it – will mean that particular specimen.
Depending on the nomenclature code applied to the organism in question, a type can be a specimen, a culture, an illustration, a description, or a taxon.
For example, in the research collection of the Natural History Museum in London, there is a bird specimen numbered 18126.96.36.199. This is a specimen of a kind of bird commonly known as the Spotted Harrier, which currently bears the scientific name Circus assimilis. This particular specimen is the holotype for that species; the name Circus assimilis refers, by definition, to the species of that particular specimen. That species was named and described by Jardine and Selby in 1828, and the holotype was placed in the museum collection so that other scientists might refer to it as necessary.
Note that at least for type specimens there is no requirement for a "typical" individual to be used. Genera and families, particularly those established by early taxonomists, tend to be named after species that are more "typical" for them, but here too this is not always the case and due to changes in systematics cannot be. Hence, the term name-bearing type or onomatophore is sometimes used, to denote the fact that biological types do not define "typical" individuals or taxa, but rather fix a scientific name to a specific operational taxonomic unit. Type specimens are theoretically even allowed to be aberrant or deformed individuals or color variations, though this is rarely chosen to be the case, as it makes it hard to determine to which population the individual belonged.
In some older taxonomic works the word "type" has sometimes been used differently. The meaning was similar in the first Laws of Botanical Nomenclature, but has a meaning closer to the term taxon in some other works:
Ce seul caractère permet de distinguer ce type de toutes les autres espèces de la section. … Après avoir étudié ces diverses formes, j'en arrivai à les considérer comme appartenant à un seul et même type spécifique.
Translation: This single character permits [one to] distinguish this type from all other species of the section ... After studying the diverse forms, I came to consider them as belonging to the one and the same specific type.
- Only a species or an infraspecific taxon can have a type of its own. For most new taxa (published on or after 1 January 2007, article 37) at these ranks a type should not be an illustration.
- A genus has the same type as that of one of its species (article 10).
- A family has the same type as that of one of its genera (article 10).
- The ICBN provides a listing of the various kinds of type (article 9), the most important of which is the holotype. Note that the word "type" appears in botanical literature as a part of several terms that have no status under the ICBN: for example a clonotype, an herbarium specimen vegetatively propagated from (and thus a clone of) the same plant from which a type specimen was made that is used for documenting the type collection.
Types in zoology Edit
In zoological nomenclature, the type of a species (or subspecies) is a specimen (or series of specimens), the type of a genus (or subgenus) is a species, and the type of a suprageneric taxon (e.g., family, etc.) is a genus. Names higher than superfamily rank do not have types. A "name-bearing type" "provides the objective standard of reference whereby the application of the name of a nominal taxon can be determined."
- A type specimen is a vernacular term (not a formally defined term) typically used for an individual or fossil that is any of the various name-bearing types for a species. For example, the type specimen for the species Homo neanderthalensis was the specimen "Neanderthal-1" discovered by Johann Karl Fuhlrott in 1856 at Feldhofer in the Neander Valley in Germany, consisting of a skullcap, thigh bones, part of a pelvis, some ribs, and some arm and shoulder bones. There may be more than one type specimen, but there is (at least in modern times) only one holotype.
- A type species is the nominal species that is the name-bearing type of a nominal genus or subgenus.
- A type genus is the nominal genus that is the name-bearing type of a nominal family-group taxon.
- The type series are all those specimens included by the author in a taxon's formal description, unless the author explicitly or implicitly excludes them as part of the series.
Use of type specimens Edit
Although in reality biologists may examine many specimens (when available) of a new taxon before writing an official published species description, nonetheless, under the formal rules for naming species (the International Code of Zoological Nomenclature), a single type must be designated, as part of the published description.
A type description must include a diagnosis (typically, a discussion of similarities to and differences from closely related species), and an indication of where the type specimen or specimens are deposited for examination. The geographical location where a type specimen was originally found is known as its Template:Visible anchor. In the case of parasites, the term type host (or symbiotype) is used to indicate the host organism from which the type specimen was obtained.
Zoological collections are maintained by universities and museums. Ensuring that types are kept in good condition and made available for examination by taxonomists are two important functions of such collections. And, while there is only one holotype designated, there can be other "type" specimens, the following of which are formally defined:
- Main article: Holotype
When a single specimen is clearly designated in the original description, this specimen is known as the holotype of that species. The holotype is typically placed in a major museum, or similar well-known public collection, so that it is freely available for later examination by other biologists.
- Main article: Paratype
A neotype is a specimen later selected to serve as the single type specimen, when an original holotype has been lost or destroyed or where the original author never cited a specimen.
A syntype is any one of two or more specimens that is listed in a species description where no holotype was designated; historically, syntypes were often explicitly designated as such, and under the present Code this is a requirement, but modern attempts to publish species description based on syntypes are generally frowned upon by practicing taxonomists, and most are gradually being replaced by lectotypes. Those that still exist are still considered name-bearing types.
In biological nomenclature, a syntype is a term used to indicate a specimen with a special status.
In zoological nomenclature, a syntype is defined as "Each specimen of a type series (q.v.) from which neither a holotype nor a lectotype has been designated [Arts. 72.1.2, 73.2, 74]. The syntypes collectively constitute the name-bearing type." (Glossary of the zoological Code ). This practice was common historically, and those syntypes which have not been replaced are still considered name-bearing types. Historically, syntypes were often explicitly designated as such. Under the present International Code of Zoological Nomenclature, for names newly published now, after 1999, it is a requirement to "expressly indicate [... those specimens ...] upon which the new taxon [i]s based [...]." (Art. 72.3 of the zoological Code). Describing species or subspecies, based on syntypes, in modern practice, is generally frowned upon by practicing taxonomists. A few exceptions are currently accepted, such as species of Huffmanela (Nematoda) described from eggs only (eggs are syntypes). A lectotype may be designated from among the syntypes, reducing the other specimens to the status of paralectotype. They are no longer name-bearing types, though if the lectotype is lost or destroyed, it is generally preferable to use a conspecific paralectotype as a replacement (neotype). Where specimens in a syntype series are found to belong to different taxa, this may cause nomenclatural instability, since the nominal species can be interpreted in different ways.
In botanical nomenclature, a syntype is defined as "any specimen cited in the protologue when there is no holotype, or any one of two or more specimens simultaneously designated as types." (Art. 9.4 of the 2006 botanical Code).
A lectotype is a specimen later selected to serve as the single type specimen for species originally described from a set of syntypes.
In botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the lectotype. A lectotype is the single specimen selected from among the syntypes to serve as the only name-bearing type specimen, and is formally designated as such. Having a single name-bearing type reduces the potential for confusion, especially considering that it is not uncommon for a series of syntypes to contain specimens of more than one species.
A paralectotype is any additional specimen from among a set of syntypes, after a lectotype has been designated from among them. These are not name-bearing types.
A special case in Protistans where the type consists of two or more specimens of "directly related individuals representing distinct stages in the life cycle"; these are collectively treated as a single entity, and lectotypes cannot be designated from among them.
Alternatives to preserved specimensEdit
Recently, some species have been described where the type specimen was released alive back into the wild, such as the Bulo Burti Boubou (a bushshrike), described as Laniarius liberatus, in which the species description included DNA sequences from blood and feather samples. Assuming there is no future question as to the status of such a species, the absence of a type specimen does not invalidate the name, but it may be necessary in the future to designate a neotype for such a taxon, should any questions arise. However, in the case of the bushshrike, ornithologists have argued that the specimen was a rare and hitherto unknown color morph of a long-known species, using only the available blood and feather samples. While there is still some debate on the need to deposit actual killed individuals as type specimens, it can be observed that given proper vouchering and storage, tissue samples can be just as valuable even in case disputes about the validity of a species arise.
Formalisation of the type systemEdit
The various types listed above are necessary because many species were described one or two centuries ago, when a single type specimen, a holotype, was often not designated. Also, types were not always carefully preserved, and intervening events such as wars and fires have resulted in destruction of original type material. The validity of a species name often rests upon the availability of original type specimens; or, if the type cannot be found, or one has never existed, upon the clarity of the description.
The ICZN has existed only since 1961, when the first edition of the Code was published. The ICZN does not always demand a type specimen for the historical validity of a species, and many "type-less" species do exist. The current edition of the Code, Article 75.3, prohibits the designation of a neotype unless there is "an exceptional need" for "clarifying the taxonomic status" of a species (Article 75.2).
There are many other permutations and variations on terms using the suffix "-type" (e.g., allotype, cotype, topotype, generitype, isotype, isoneotype, isolectotype, etc.) but these are not formally regulated by the Code, and a great many are obsolete and/or idiosyncratic. However, some of these categories can potentially apply to genuine type specimens, such as a neotype; e.g., isotypic/topotypic specimens are preferred to other specimens, when they are available at the time a neotype is chosen (because they are from the same time and/or place as the original type).
The term fixation is used by the Code for the declaration of a name-bearing type, whether by original or subsequent designation.
Type species Edit
- Main article: Type species
Each genus must have a designated type species (the term "genotype" was once used for this but has been abandoned because the word has been co-opted for use in genetics and is much better known in that context). The description of a genus is usually based primarily on its type species, modified and expanded by the features of other included species. The generic name is permanently associated with the name-bearing type of its type species.
Ideally, a type species best exemplifies the essential characteristics of the genus to which it belongs, but this is subjective and, ultimately, technically irrelevant, as it is not a requirement of the Code. If the type species proves, upon closer examination, to belong to a pre-existing genus (a common occurrence), then all of the constituent species must be either moved into the pre-existing genus, or disassociated from the original type species and given a new generic name; the old generic name passes into synonymy and is abandoned unless there is a pressing need to make an exception (decided case-by-case, via petition to the International Commission on Zoological Nomenclature).
Type genus Edit
- Main article: Type genus
A type genus is that genus from which the name of a family or subfamily is formed. As with type species, the type genus is not necessarily the most representative, but is usually the earliest described, largest or best known genus. It is not uncommon for the name of a family to be based upon the name of a type genus that has passed into synonymy; the family name does not need to be changed in such a situation.
See also Edit
- ↑ de Candolle, A.P. (1867). Lois de la nomenclature botanique adoptées par le Congrès International de Botanique tenu à Paris en août 1867 suivies d'une deuxième édition de l'introduction historique et du commentaire qui accompagnaient la rédaction préparatoire présentée à la congrès, Genève et Bale: J.-B. Baillière et fils.
- ↑ Weddell (1868). Laws of Botanical Nomenclature adopted by the International Botanical Congress held at Paris in August 1867; together with an Historical Introduction and Commentary by Alphonse de Candolle, Translated from the French; Reprinted from the English translation published by L. Reeve and Co., London, 1868 (with three-page commentary by Asa Gray). The American Journal of Science and Arts Series II, Volume 46 (63–74, 75–77).
- ↑ Crépin, F. (1886). Rosa Synstylae: études sur les roses de la section Synstyleés. Bulletin de la Société Royale de Botanique de Belgique 25 (2: Comptes-redus des séances de la Société Royale de Botanique de Belgique): 163–217.
- ↑ Frey, Jennifer K.; Yates, Terry L.; Duszynski, Donald W.; Gannon, William L.; and Gardner, Scott L. (1992). Designation and Curatorial Management of Type Host Specimens (Symbiotypes) for New Parasite Species. The Journal of Parasitology 78 (5): 930–993.
- ↑ ICZN (1999). International Code of Zoological Nomenclature.
- ↑ 6.0 6.1 6.2 Daniel L. Geiger (2006). "Taxonomy and taxonomic writing: a primer" Charles F. Sturm, Timothy A. Pearce, Ángel Valdés The Mollusks: a Guide to Their Study, Collection, and Preservation, 147–159, Universal-Publishers.
- ↑ Carden C. Wallace (1999). "Summary of type material" Staghorn Corals of the World: a Revision of the Coral Genus Acropora (Scleractinia; Astrocoeniina; Acroporidae) Worldwide, with Emphasis on Morphology, Phylogeny and Biogeography, 7–19, CSIRO Publishing.
- ↑ McNeill & al. (2006). International Code of Botanical Nomenclature.
- ↑ Stearn, W. T. 1959. "The background of Linnaeus's contributions to the nomenclature and methods of systematic biology", Systematic Zoology 8 (1): 4-22, p. 4
- ↑ (25 June 2007)Reappraisal of the parrots (Aves: Psittacidae) from the Mascarene Islands, with comments on their ecology, morphology, and affinities. Zootaxa (1513): 1–76.