Define monophyletic | Dictionary and Thesaurus

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« Define monophthongalDefine monophyletismGo to User ContributedDictionaryGo to ExtensiveDefinitionUser ContributedDictionaryEnglishAdjectiveOf, pertaining to, or affecting a single phylum (or other taxon) of organismsDeriving from a single biological sourceRelated termsmonophylyExtensive DefinitionA clade is a taxonomic group (such as one oforganisms) comprising asingle commonancestor and all the descendants of that ancestor. Any suchgroup is considered to be a monophyletic group, and can berepresented by both a phylogenetic analysis, asin a tree diagram, and by a cladogram (see cladistics), or simply as ataxonomic reference. If a clade proves robust in alternatecladistic analyses using different sets of data, it may be adoptedinto taxonomy and become a taxon. Not all taxa, however, are considered to beclades. Reptiles, forexample, are a paraphyletic group becausethey do not include aves(birds), which are thoughtto also have evolved from the common ancestor of thereptiles.In cladistics, a clade that islocated within another more inclusive clade is said to be "nested"within that clade. Nested clade analysis is beneficial in manyways. For instance, it enables the detection of range expansions inisolated geographic areas.Phylogenetic nomenclaturePhylogeneticnomenclature is formulated in terms of evolution and commondescent rather than the typespecimens, categorical ranks, and morphologicalcharacters.The latter is used most commonly in cladistic analysis. Taxon namesare strictly connected to phylogenetictree topology and evolutionary history. In taxonomy, each nameis attached to a clade taxonomic group containing a common ancestorand all its descendants. Phylogenetic nomenclature discardscategorical ranks. The problem with ranks are evident when oneconsiders biodiversity lineages andclades. Questions like "how many lineages are there?" or "how manyclades are there?" become pointless, since there are no answers.These are relative concepts, illustrating the fractal nature of thetree of life and the need to let a phylogenetic hypothesis be thefocus, rather than the categories, when biodiversity is quantified.Phylogenetic nomenclature helps to put focus on phylogenetic treesby offering an explicit link between names and parts of specieshistory, that is, clades.Traditional binomial nomenclatureIn phylogenetics, binomialnames are associated with the relationships of each describedspecies. But this creates a problem because it makes assumptionsabout relationships about the description of the speciesidentification. It suggests that species or genera are a uniquecategory, and this contradicts the idea of recognizing only cladesand lineages.Relation to paraphyletic and polyphyletic groupsGroupsthat do not include all the descendants of the most recent commonancestor are said to be paraphyletic. For example,as shown in the adjacent illustration, reptiles are paraphyleticbecause that group excludes birds. A group that does not containthe most recent common ancestor of its members is said to bepolyphyletic (Greekpolys = many). An example of a polyphyletic group is thewarm-blooded animals.Phylogenetic alternativesTo avoid the pitfalls of traditional Linnaeantaxonomy in phylogenetic nomenclature, three new methods ofphylogenetic naming have been proposed: node-, stem-, andapomorphy-based. In node-based naming, taxon name A might refer tothe least inclusive clade containing X and Y. In stem-based naming,A would refer to the most inclusive clade containing X and Y butnot Z. In apomorphy (derived feature)-based naming, A would referto the clade identified by a feature synapomorphic (sharing aderivation) with a feature in specimen (taxon) X. Differencesbetween a traditional approach and these phylogenetic alternativesbecome obvious when the phylogenetic hypothesis changes. Comparisonbetween the traditional Linnaean approach to nomenclature and aphylogenetic alternative (node-based naming). Suppose that all wewant to do is to give a name ("A") to a clade containing X and Y.In the Linnaean system this means that we have to introduce namesfor sister taxa, assigning all taxa to the categories species,genus, and family, and designate type species. No explicitreference to phylogeny is made. The phylogenetic alternativeprovides an explicit reference to evolutionary history, and nothingbut the clade containing X and Y needs to be named. When thehypothesis of relationship changes, the phylogenetic alternative iscleaner and more explicit about what it refers to.ReferencesExternal linksEvolvingThoughts: CladeAposter-sized cladogram showing the Tree of Life (Evolution)DMHillis, D Zwickl R Gutell: ~3000 species Tree of Life Acladogram?Phylogenetic systematics, an introductory slide-show onevolutionary trees University of California, Berkeleymonophyletic in Arabic: كليدmonophyletic in Catalan: Clademonophyletic in German: Monophyliemonophyletic in Spanish: Cladomonophyletic in Estonian: Klaadmonophyletic in Esperanto: Kladomonophyletic in French: Clademonophyletic in Indonesian: Kladmonophyletic in Italian: Clademonophyletic in Hungarian: Kládmonophyletic in Maltese: Kladmonophyletic in Malay (macrolanguage):monophyletic in Dutch: Clademonophyletic in Norwegian: Klademonophyletic in Polish: Kladmonophyletic in Portuguese: Cladomonophyletic in Russian: Кладаmonophyletic in Simple English: Clademonophyletic in Slovenian: Kladmonophyletic in Finnish: Kliinimonophyletic in Swedish: Kladmonophyletic in Ukrainian:Клада

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