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For other uses, see Clade (disambiguation).

A clade (from Ancient Greek: κλάδος, klados, "branch") or monophylum (see monophyletic) is a group consisting of an ancestor and all its descendants, a single "branch" on the "tree of life".[1] The ancestor may be an individual, a population or even a species (extinct or extant). Many familiar groups, rodents and insects for example, are clades; others, like lizards and monkeys, are not (lizards excludes snakes, monkeys excludes apes and humans).

Cladogram (family tree) of a biological group (ancestor at the bottom). The red and blue boxes at right and left represent clades (i.e., complete branches). The green box in the middle is not a clade, but rather represents an evolutionary grade, an incomplete group, because the blue clade at left is descended from it, but is excluded.

Increasingly, taxonomists try to avoid naming taxa that are not clades.

Etymology[edit]

The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis, a concept Huxley borrowed from Bernhard Rensch.[1][2]

Definitions[edit]

Gavialidae, Crocodylidae and Alligatoridae are clade names that are here applied to a phylogenetic tree of crocodylians.

Clade and ancestor[edit]

A clade is by definition monophyletic, meaning it contains one ancestor (which can be an organism, a population, or a species) and all its descendants.[note 1][3][4] The ancestor can be known or unknown; any and all members of a clade can be extant or extinct.

Clades and phylogenetic trees[edit]

Main article: Phylogenetics
Main article: Cladistics

The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics, the latter term being derived from "clade" by Ernst Mayr (1965). The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms; they, and all their branches, are phylogenetic hypotheses.[5]

Three methods of defining clades are featured in phylogenetic nomenclature: node-, stem-, and apomorphy-based (see here for detailed definitions).

Terminology[edit]

Cladogram of the primates, showing the nested nature of the primate tree

The relationship between clades can be described in several ways:

  • A clade located within a clade is said to be nested within that clade. In the diagram, the hominoid clade, the apes and humans, is nested within the primate clade.
  • Two clades are sisters if they have an immediate common ancestor. In the diagram, lemurs and lorises are sister clades.
  • A clade A is basal to a clade B if A branches off the lineage leading to B before the first branch leading only to members of B. In the diagram to the right, the strepsirrhine clade, including the lemurs and lorises, is basal to the hominoids, the apes and humans. Some authors have used "basal" differently, using it to mean a clade that is "more primitive" or less species-rich than its sister clade; others consider this usage to be incorrect.[6]

Nomenclature and taxonomy[edit]

Early phylogenetic tree by Haeckel, 1866

The idea of a clade did not exist in pre-Darwinian Linnaean taxonomy, which was based by necessity only on internal or external morphological similarities between organisms – although as it happens, many of the better known animal groups in Linnaeus' original Systema Naturae (notably among the vertebrate groups) do represent clades. The phenomenon of convergent evolution is however responsible for many cases where there are misleading similarities in the morphology of groups that evolved from different lineages.

With the publication of Darwin's theory of evolution in 1859, the idea was born that groups used in a system of classification should represent branches on the evolutionary tree of life. In the century and a half since then, taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming, however, this principle is not always compatible with the traditional rank-based nomenclature. In the latter, only taxa associated with a rank can be named, yet there are not enough ranks to name a long series of nested clades; also, taxon names cannot be defined in a way that guarantees them to refer to clades. For these and other reasons, phylogenetic nomenclature has been developed; it is still controversial.

See also[edit]

Notes[edit]

  1. ^ A semantic case has been made that the name should be "holophyletic," but this term has not acquired widespread use. For more information, see holophyly

References[edit]

  1. ^ a b Dupuis, Claude (1984). "Willi Hennig's impact on taxonomic thought". Annual Review of Ecology and Systematics 15: 1–24. doi:10.1146/annurev.es.15.110184.000245. 
  2. ^ Huxley, J. S. (1957). "The three types of evolutionary process". Nature 180: 454–455. doi:10.1038/180454a0. 
  3. ^ "International Code of Phylogenetic Nomenclature. Version 4c. Chapter I. Taxa.". 2010. Retrieved 22 September 2012. 
  4. ^ Envall, Mats (2008). "On the difference between mono-, holo-, and paraphyletic groups: a consistent distinction of process and pattern". Biological Journal of the Linnean Society 94: 217. doi:10.1111/j.1095-8312.2008.00984.x. 
  5. ^ Nixon, Kevin C.; Carpenter, James M. (1 September 2000). "On the Other "Phylogenetic Systematics"". Cladistics 16 (3): 298–318. doi:10.1111/j.1096-0031.2000.tb00285.x. 
  6. ^ Krell, F.-T. & Cranston, P. (2004). "Which side of the tree is more basal?". Systematic Entomology 29 (3): 279–281. doi:10.1111/j.0307-6970.2004.00262.x. 

External links[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Clade — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.

96 news items

 
Nature.com
Tue, 26 Aug 2014 23:17:00 -0700

... the highest 16S rRNA gene similarity of 98.8% to A. albata and clustered with A. albata and A. multivorans in the 16S rRNA gene tree, which formed a well separated clade supported by a 99% bootstrap value in the family Pseudonocardiaceae (Figure 1).
 
Nature.com
Fri, 22 Aug 2014 06:57:19 -0700

Bacteria of the marine Roseobacter clade are characterised by their ability to utilise a wide range of organic and inorganic compounds to support growth. Trimethylamine (TMA) and trimethylamine N-oxide (TMAO) are methylated amines (MA) and form part of ...
 
Sci-Tech Today
Wed, 20 Aug 2014 09:41:15 -0700

In what was once a desert in southern Brazil, scientists have discovered a lizard with a wingspan of 2 to 8 feet. The Caiuajara dobruskii is a a member of the order Pterosauria, a clade of flying lizards that lived during the time of the dinosaurs ...

Scientific American (blog)

Scientific American (blog)
Wed, 20 Aug 2014 18:34:41 -0700

Tits are passerines, and are undeniably and obviously part of Passerida, the great clade that includes sparrows, finches, thrushes, larks, swallows, Old Word warblers and so on. But where do they belong within this group? That's been hard to answer ...
 
GhanaWeb
Fri, 22 Aug 2014 17:00:00 -0700

Let us look at the question from another angle: Given that the sick “scholar” is a primate himself, what makes him think he is more intelligent and more human than his primatial clade? The latter defines the national dilemma, a blurry overlap between ...

Sci-News.com

Sci-News.com
Thu, 14 Aug 2014 06:49:06 -0700

“Several features of the Caiuajara dobruskii head differ from all other members of this clade, including the presence of a bony expansion projecting inside the large opening in the skull in front of the eyes, and the rounded depressions in the outer ...
 
Investing.com
Sun, 10 Aug 2014 01:03:45 -0700

An agreement has been signed granting rights to Valneva's EB66 cell line for clinical and commercial production of the MVA component of Geovax Labs Inc's (OTC:GOVX) preclinical clade C HIV vaccines for the developing world. This will allow for ...

Tech Times

Tech Times
Sat, 16 Aug 2014 20:00:48 -0700

Many features of its head vary from the other members of this clade, such as the strange bony expansion that project inside the big skull opening in front of the eyes as well as the rounded depressions seen in the outer surface of its jaw. Both young ...
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