Διαφορά μεταξύ των αναθεωρήσεων του «Κλάδος»

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αρχή μτφρ από το en:Clade
(αρχή μτφρ από το en:Clade)
[[File:Clade-grade II.svg|thumb|right|334 px|Κλαδόγραμμα (οικογενειακό δέντρο) μίας βιολογικής ομάδας. Τα επισημασμένα με κόκκινο και μπλε τμήματα αναπαριστούν ''κλάδους''. Αυτά με πράσινο δεν αναπαριστούν κλάδο, αλλά μία [[εξελικτική βαθμίδα]], μία ατελή ομάδα, επειδή ο μπλε κλάδος κατάγεται από αυτήν αλλά αποκλείεται.]]
[[File:Clade-grade II.svg|thumb|right|334 px|Cladogram (family tree) of a biological group. The red and blue boxes represent ''clades'' (i.e., complete branches). The green box is not a clade, but rather represents an ''[[evolutionary grade]]'', an incomplete group, because the blue clade descends from it, but is excluded.]]
A '''cladeΚλάδος'''<ref group=note>(fromείναι [[Ancientμία Greek]]ομάδα ''{{Polytonic|κλάδος}}'',που ''klados'',αποτελείται "branch")</ref>από isένα aοργανισμό groupκαι consistingόλους ofτους anαπογόνους organism and all its descendantsτου. InΣε theόρους terms ofτης [[systematics|biological systematicsσυστηματική]]ς, aο cladeκλάδος isείναι aένα singleμονό "branch"κλαδί onτου the "[[Treeδέντρο ofτης life (science)ζωής|treeδέντρου ofτης lifeζωής]]".<ref name=Dupuis>{{cite journal | last=Dupuis | first=Claude | year=1984 | title=Willi Hennig's impact on taxonomic thought | journal=Annual Review of Ecology and Systematics | volume=15 | pages=1–24 | issn=0066-4162}}</ref> TheΗ ideaιδέα thatότι suchμία aτέτοια "naturalφυσική group"ομάδα ofοργανισμών organismsθα shouldέπρεπε beνα groupedομαδοποιείται togetherκαι andτης givenδίνεται aένα [[Taxonomyταξινομία|taxonomicταξινομικό]] nameόνομα είναι isκεντρική centralιδέα toτης [[biologicalβιολογική classificationταξινόμηση|βιολογικής ταξινόμησης]]. InΣτην [[cladisticsκλαδιστική]] (whichη takesοποία itsπήρε nameτο fromόνομά theτης termαπό τον όρο), cladesοι κλάδοι areείναι theοι onlyμόνες acceptableαποδεκτές unitsμονάδες.
TheΟ termόρος wasεισήχθη coined inτο 1958 byαπό [[England|English]]τον Άγγλο biologistβιολόγο [[JulianΤζούλιαν HuxleyΧάξλεϊ]].<ref name=Dupuis/>
== Ορισμοί ==
[[File:Cladogram Crocodilia NL.PNG|thumb|right|200 px|[[Κλαδόγραμμα]] των κροκοδείλων, οπτική αναπαράσταση των σχέσεών τους.]]
{{main|Phylogenetic nomenclature#Phylogenetic definitions|l1=Phylogenetic definitions}}
[[File:Cladogram Crocodilia NL.PNG|thumb|right|200 px|A [[cladogram]] of crocodiles, a visual representation of their relationship]]
===Clade and ancestor===
A clade is termed [[monophyletic]], meaning it contains one ancestor which can be an organism, [[population]], or [[species]] and all its descendants.<ref group=note>
A semantic case has been made that the name should be "holophyletic," but this term has not yet acquired widespread use. For more information, see ''[[holophyly]]''</ref><ref>{{cite web|title=The PhyloCode, Chapter 1|url=http://www.ohio.edu/phylocode/art1-3.html#chapter1|year=2009|publisher=International Society for Phylogenetic Nomenclature|accessdate=23 January 2010}}</ref><ref>{{cite journal
| doi = 10.1111/j.1095-8312.2008.00984.x
| title = On the difference between mono-, holo-, and paraphyletic groups: a consistent distinction of process and pattern
| year = 2008
| last = Envall
| first= Mat S.
| journal = Biological Journal of the Linnaean Society
| volume = 94
| page = 217 }}</ref> The term clade refers to the grouping of the ancestor and its living and/or deceased descendants together. The ancestor can be a theoretical or actual species.
===Κλάδος και πρόγονοι===
===Clade definition===
Ένας κλάδος είναι εξ ορισμού [[μονοφυλετικός]], καθώς περιέχει ένα πρόγονο ο οποίος μπορεί να είναι ένας οργανισμός, ένας [[πληθυσμός]] ή ένα [[είδος (βιολογία)|είδος]] και όλοι τους οι απόγονοι..<ref group="Σημ.">
Three methods of defining clades are featured in [[phylogenetic nomenclature]]: node-, stem-, and apomorphy-based:
Έχει διατυπωθεί η άποψη ότι το όνο θα έπρεπε να είναι «ολοφυλετικός» αντί για «μονοφυλετικός», όμως αυτός ο όρος δεν έχει ακόμα ευρεία χρήση.</ref><ref>{{cite web|title=The PhyloCode, Chapter 1|url=http://www.ohio.edu/phylocode/art1-3.html#chapter1|year=2009|publisher=International Society for Phylogenetic Nomenclature|accessdate=23 January 2010}}</ref><ref>{{cite journal | doi = 10.1111/j.1095-8312.2008.00984.x | title = On the difference between mono-, holo-, and paraphyletic groups: a consistent distinction of process and pattern | year = 2008 | last = Envall | first= Mat S. | journal = Biological Journal of the Linnaean Society | volume = 94 | page = 217 }}</ref> Ο όρος κλάδος αναφέρεται στον πρόγονο και τους επιζώντες ή/και εκλιπώντες απόγονούς του. Ο δε πρόγονος μπορεί να είναι θεωρητικό είτε πραγματικό είδος.
* In node-based definition, clade name A refers to the ''least inclusive'' clade containing taxa (or specimens) X, Y, etc., and their common ancestor. The ancestor is the branch point, or ''node''.
* In stem-based definition, A refers to the ''most inclusive'' clade containing X, Y, etc., and their common ancestor, down to where Z branches off below A. Taxa are included between the node of A and down to (but not including) the branching point to Z; that is, the ''[[Crown group#Stem groups|stem]]'' of A.
* In [[apomorphy]]-based definition, A refers to the clade identified by an apomorphy (a trait) found in X, Y, etc., and their common ancestor.
===Οι κλάδοι ως δομές===
In [[Linnaean taxonomy]], clades are defined by a set of traits (apomorphies) unique to the group. This system is basically similar to the apomorphy-based clades of phylogenetic nomenclature. The difference is one of weight: While phylogenetic nomenclature bases the group on an ancestor with a certain trait, Linnaean taxonomy uses the traits themselves to define the group.
Στην [[κλαδιστική]], ο κλάδος είναι μία υποθετική δομή, βασιμένη σε πειραματικά δεδομένα. Οι κλάδοι υπολογίζονται με την χρήση πολλαπλών (κάποιες φορές εκατοντάδων) χαρακτηριστικών ενός αριθμού ειδών (ή δειγμάτων) και την [[στατιστική]] τους ανάλυση ώστε να βρεθεί το πιο πιθανό φυλογενετικό δέντρο για την ομάδα. Αν και παρόμοια κατά κάποιο τρόπο με την [[συστηματική ταξινόμηση]], η μέθοδος είναι πιο ανοικτή στον αυστηρό έλεγχο από ότι οι παραδοσιακές μέθοδοι. Παρόλο που οι ταξινομιστές χρησιμοποιούν τους κλάδους ως εργαλεία στην ταξινόμηση όποτε είναι αφικτό, το ταξινομικό [[δέντρο της ζωής]] δεν είναι το ίδιο με το κλαδιστικό. Τα παραδοσιακά γένη, οικογένειες, κτλ δεν είναι κατ' ανάγκη κλάδοι, αν και συχνά είναι.
=== Ονόματα κλάδων ===
===Clades as constructs===
Στη συστηματική του Λινναίου, οι διάφορες ομάδες ταξινομούνται σε μία σειρά από [[ταξινομική βαθμίδα|ταξινομικές βαθμίδες]] (όπως [[τάξη (βιολογία)]], [[οικογένεια (βιολογία)|οικογένεια]] κτλ). Υπάρχει σύμβαση το όνομα κάποιων ομάδων να εξαρτάται από την βαθμίδα. Για τους κλάδους από την φύση τους αυτό δεν ισχύει, και δεν υπάρχει κάποιος περιορισμός ως προς το όνομά τους στην [[κλαδιστική]]. Υπάρχει ωστόσο σύμβαση για την ονομασία λιγότερο ή περισσότερο περιεκτικών ομάδων, στις οποίες δίνονται προθέματα όπως ''crown-'' ή ''pan-''.
In [[cladistics]], the clade is a hypothetical construct based on experimental data. Clades are found using multiple (sometimes hundreds) of traits from a number of species (or specimens) and [[analysis|analysing]] them [[statistics|statistically]] to find the most likely phylogenetic tree for the group. Although similar in some ways to a [[biological classification]] of species, the method is statistical and more open to scrutiny than traditional methods. Although taxonomists use clades as a tool in classification where feasible, the taxonomic "[[Tree of life (science)|tree of life]]" is not the same as the cladistic. The traditional genus, family, etc. names are not necessarily clades; though they will often be.
== Σημειώσεις ==
===Clade names===
In Linnaean systematics, the various groups are ordered into a series of [[taxonomic rank]]s (the familiar [[order (biology)|order]], [[family (biology)|family]] etc). These ranks will by convention dictate the ending to names for some groups. Clades do not by their nature fit this scheme, and no such restriction exists as to their names in [[cladistics]]. There is however a convention for naming more or less inclusive groups, which are given prefixes like ''crown-'' or ''pan-'', see [[Crown group]].
== Παραπομπές ==
==Taxonomy and systematics==
[[File:Haeckel arbol bn.png|thumb|right|Early phylogenetic tree by [[Ernst Haeckel|Haeckel]], 1866]]
The idea of "clade" did not exist in pre-[[Charles Darwin|Darwinian]] [[Linnaean taxonomy]], which was based only on [[morphology (biology)|morphological]] similarities between organisms, though many of the better known animal groups in Linnaeus' original [[Systema Naturae]] (notably among the [[vertebrate]] groups) represent clades. With the publication of Darwin's [[Evolution|theory of evolution]] in 1859, taxonomy gained a theoretical basis, and the idea that systematic units represent branches on the evolutionary [[tree of life]] was born. In the century and a half since then, taxonomists have worked to make the taxonomic system reflect evolution. However, as the Tree of Life branches rather unevenly, the [[hierarchy]] of the Linnaean system does not always lend itself well to represent clades. When it comes to [[Nomenclature#Biology|naming]], [[cladistics]] and [[Linnaean taxonomy]] are not always compatible. Particularly higher level taxons in Linnaean taxonomy often represent [[evolutionary grade]]s rather than clades, i.e. clades where one or two sub-branches have been excluded. Typical examples include [[Osteichthyes|bony fishes]], who include the ancestor of [[tetrapoda|tetrapods]], and [[reptiles]], ancestral to both [[bird]]s and [[mammal]]s.<ref group=note>The term "reptile" is here to be understood as traditionally defined, e.g. Romer & Parson (1985): ''The Vertebrate Body.'' (6th ed.) Saunders, Philadelphia. There are other (cladistic) definitions of "reptile" that exclude the first [[amniote]]s and the [[synapsid]] line, see [[Sauropsida]].</ref>
In [[phylogenetic nomenclature]], clades can be nested at any level, and do not have to be slotted into a [[ranking|rank]] in an overall hierarchy. In contrast, the Linnaean units of "[[order (biology)|order]]", "[[class (biology)|class]]" etc. must be used when naming a new taxon. As there are only seven formal levels to the Linnaean system (whereof [[species]] is the lowest), there is a finite amount of sub- and super-units that can be applied. As taxonomic trees ([[cladogram]]s) become more detailed, some researchers intimately familiar with the topography of the trees they are working with have opted to dispense with the ranks all together, using clade names without Linnaean ranks. The preference of one system over the other is mainly one of application: Cladistics give details, but require intimate knowledge; the Linnaean system gives a well ordered overview, at the expense of details of the phylogenetic tree.
In a few instances, the Linnaean system has actually impeded our understanding of the phylogeny and broad evolutionary patterns. The best known example is the interpretation of the strange [[fossils of the Burgess Shale]] and the subsequent idea of a "[[Cambrian Explosion]]"
<ref name=Budd2000>{{Cite journal
| last1 = Budd | first1 = G.E.
| last2 = Jensen | first2 = S.
| year = 2000
| title = A critical reappraisal of the fossil record of the bilaterian phyla
| journal = Biological Reviews
| volume = 75
| issue = 02
| pages = 253–295
| url = http://journals.cambridge.org/production/action/cjoGetFulltext?fulltextid=624
| doi = 10.1017/S000632310000548X
With the application of cladistics, and the rejection of any significance of the concept of [[Phylum|Phyla]], the confusion of the late 20th century over the Burgess animals has been resolved. It appears there never was an "explosion" of major [[bauplan]]s with subsequent [[extinction]]s.<ref>{{cite journal | author = Erwin, D.H.| year = 2007| doi = 10.1111/j.1475-4983.2006.00614.x| title = Disparity: Morphological Pattern And Developmental Context| journal = Palaeontology| volume = 50| pages = 57 }}</ref> The seemingly weird critters themselves have been found to be representatives of a group, the [[Lobopodia]], that includes [[Arthropoda|arthropods]], [[Tardigrada|water bears]] and [[Onychophora|velvet worms]].<ref>{{Cite journal
| author1 = | first1 = R. J.
| author2 = | first2 = S. E.
| author3 = | first3 = R. J.
| last1 = Whittle
| author4 = | first4 = J.
| title = An Ordovician Lobopodian from the Soom Shale Lagerstätte, South Africa
| journal = Palaeontology
| volume = 52
| pages = 561–567
| year = 2009
| doi = 10.1111/j.1475-4983.2009.00860.x
| last2 = Gabbott
| last3 = Aldridge
| last4 = Theron
In most instances the two systems are not at odds, however. The cladistic statement, that the clade Lobopodia contains (among others) the Arthropoda, Tardigrada and Onychophora, is factually identical to the Linnaean evolutionary statement that the group Lobopodia is ancestral to the phyla Arthropoda, Tardigrada and Onychophora. The difference is one of semantics rather than phylogeny.
== See also ==
* [[Cladistics]]
* [[Phylogeny]]
* [[Paraphyly]]
* [[Polyphyly]]
* [[Phylogenetic nomenclature]]
* [[Binomial nomenclature]]
* [[Crown group]]
<references group=note/>
==References==<!-- OrgDiversEvol8:17. ZoolScripta36:607,37:337,38:101. -->
==External links==
* [http://scienceblogs.com/evolvingthoughts/2007/01/clade_1.php Evolving Thoughts: Clade]
* DM Hillis, D Zwickl & R Gutell. "[http://www.zo.utexas.edu/faculty/antisense/DownloadfilesToL.html Tree of life]". An unrooted cladogram depicting around 3000 species.
* [http://evolution.berkeley.edu/evolibrary/article/0_0_0/phylogenetics_01 Phylogenetic systematics, an introductory slide-show on evolutionary trees] [[University of California, Berkeley]]
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