Jump to content

Sister group: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous edit
Content deleted Content added
VisualWikitext
m wording
m Style
 
(39 intermediate revisions by 19 users not shown)
Line 1: Line 1:
{{Short description|The closest relative(s) of another given taxon in a phylogenetic tree}}
{{Short description|The closest relative(s) of another given taxon in a phylogenetic tree}}
A '''sister group''' or '''sister taxon''' is a [[phylogenetic]] term denoting the closest relative(s) of another given unit in an [[evolutionary tree]].<ref name=Fullerton>{{cite web |last=Eernisse |first=Douglas J. |title=Introduction to Phylogeny: What is a Sister Taxon? |url=http://biology.fullerton.edu/biol404/phylo/sisters.html |work=Biology 404 - Evolution |publisher=Department of Biological Science, [[California State University]], Fullerton |accessdate=4 January 2012}}</ref>
In [[phylogenetics]], a '''sister group''' or '''sister taxon''', also called an '''adelphotaxon''',<ref>[https://eurekamag.com/research/002/538/002538285.php Ultrastructural evidence for an adelphotaxon (sister group) to the Neodermata (Platyhelminthes)]</ref> comprises the closest relative(s) of another given unit in an [[evolutionary tree]].<ref name=Fullerton>{{cite web |last=Eernisse |first=Douglas J. |title=Introduction to Phylogeny: What is a Sister Taxon? |url=http://biology.fullerton.edu/biol404/phylo/sisters.html |work=Biology 404 - Evolution |publisher=Department of Biological Science, [[California State University]], Fullerton |access-date=4 January 2012}}</ref>


== Definition ==
== Definition ==
The expression is most easily illustrated by a [[cladogram]]:
The expression is most easily illustrated by a [[cladogram]]:


⚫
{{cladogram
{{barlabel
|title=Sister group relationships
|size=4
|at1=2
|align=center
|cladogram= {{small| }}
|color=red
{{clade | style=width:400px; thickness=1
|label1=Clade AB
⚫
|label1 = &nbsp; Root &nbsp;
⚫
|cladogram=
{{clade
|1={{clade |thickness=1
|label1=
|label1= &nbsp; Subtree &nbsp;
|1={{clade
|1={{clade |thickness=3
|style=background-color:#ffdddd;
|1={{clade
|grouplabelstyle1=background-color:#ffffcc; color:blue; vertical-align:middle;
⚫
|label1 = &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
|1= &nbsp; [[Taxon]] A &nbsp; |barbegin1=red
|grouplabel1=[[Clade]] <br> &nbsp; '''AB'''
|2= &nbsp; Taxon B &nbsp; |barend2=red
|1={{clade |thickness=3
|style=background-color:#ffffcc;
⚫
|label1 = &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
|1= &nbsp; [[Taxon]] '''A''' &nbsp; &nbsp;
|barbegin1=blue
|2= &nbsp; Taxon '''B''' &nbsp; &nbsp;
|barend2=blue
}}
|2= &nbsp; Taxon '''C''' &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
|label2 = &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
}}
}}
|grouplabelstyle1=background-color:#ffdddd;vertical-align:middle;
⚫
|2= &nbsp; Taxon C &nbsp;
|grouplabel1=Clade <br>&nbsp;'''ABC'''
|bar1=purple
|label2 = &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
|label2 = &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
|2= &nbsp; More tree branches &nbsp;
}}
}}
}}
}}
}}
}}


The sister group to [[taxon|taxon A]] is taxon B; conversely, the sister group to taxon B is taxon A. Taxa A and B, together with all other descendants of their [[most recent common ancestor]], form a [[monophyletic]] group, the [[clade]] AB. The sister group to clade AB is taxon C, and conversely, the sister group to taxon C is clade AB.
[[Taxon]] A and taxon B are sister groups to each other. Taxa A and B, together with any other [[Extant taxon|extant]] or [[Extinction|extinct]] descendants of their [[most recent common ancestor]] (MRCA),{{refn|group=Note|A tree diagram inevitably oversimplifies the complicated process of evolution.}} form a [[monophyletic]] group, the [[clade]] AB. Clade AB and taxon C are also sister groups. Taxa A, B, and C, together with all other descendants of their MRCA form the clade ABC.


The whole clade ABC is itself a subtree of a larger tree, which offers yet more sister group branches that are farther removed from the [[Tree_(data_structure)#Terminology_used_in_trees|leaf nodes]], such as taxa A, B, and C.
The whole clade ABC is itself a subtree of a larger tree which offers yet more sister group relationships, both among the [[Tree_(data_structure)#Terminology_used_in_trees|leaves]] and among larger, more deeply [[Phylogenetic tree#Rooted tree|rooted]] clades. The tree structure shown connects through its root to the rest of the [[Tree of life (biology)|universal tree of life]].


In [[cladistics|cladistic]] standards, taxa A, B, and C may represent specimens, [[species]], [[genera]], or any other taxonomic units. If they represent species, the term ''sister species'' is sometimes used.
In [[cladistics|cladistic]] standards, taxa A, B, and C may represent specimens, [[species]], [[genera]], or any other taxonomic units. If A and B are at the same taxonomic level, terminology such as ''sister species'' or ''sister genera'' can be used.


== Example ==
== Example ==
[[File:Dinosauria phylogeny (within Archosauriformes).png|thumb|A Dinosauria phylogeny including two extant taxa: birds ([[Theropoda]]) and crocodiles ([[Suchia]]).]]
[[File:Dinosauria phylogeny (within Archosauriformes).png|thumb|left|600px| {{center|A [[Dinosauria]] phylogeny including two extant taxa: birds ([[Theropoda]]) and crocodiles ([[Suchia]]).}} ]]
The term ''sister group'' is used in [[phylogenetic analysis]], however, only groups identified in the analysis are labeled as "sister groups".
The term "sister group" is used in [[phylogenetic analysis]], and only groups identified in the analysis are labeled as sister groups. An example is in [[birds]], whose sister group is commonly cited as the [[crocodilia|crocodiles]], but that is true only when dealing with [[extant taxa]].<ref>{{cite journal |last=Padian |first=Kevin |author2=Lindberg, David R. |author3=Polly, Paul David |title=Cladistics and the Fossil Record: The Uses of History |journal=Annual Review of Earth and Planetary Sciences |date=1 May 1994 |volume=22 |issue=1 |pages=63–89 |doi=10.1146/annurev.ea.22.050194.000431}}</ref><ref>{{cite journal |last=Kemp |first=T.S. |title=Haemothermia or Archosauria? The interrelationships of mammals, birds and crocodiles|journal=Zoological Journal of the Linnean Society |date=1 January 1988|volume=92|issue=1|pages=67–104|doi=10.1111/j.1096-3642.1988.tb01527.x}}</ref> The bird family tree is rooted in the [[dinosaur]]s, and there were a number of extinct groups branching off of dinosaurs before coming to the last common ancestor of birds and crocodiles.<ref>{{cite web|last=Hughes|first=J.M.|title=Ancient bird-crocdilian ancestor uncovered|url=http://www.avesvitae.org/www.avesvitae.org/News/Entries/2011/6/13_Ancient_Bird-Crocodilian_Ancestor_Uncovered.html|work=AVES VITAE - The lives of birds|accessdate=4 January 2012|url-status=dead|archiveurl=https://web.archive.org/web/20120426091546/http://www.avesvitae.org/www.avesvitae.org/News/Entries/2011/6/13_Ancient_Bird-Crocodilian_Ancestor_Uncovered.html|archivedate=26 April 2012}}</ref> Thus, the term sister group must be seen as a relative term, with the caveat that the sister group is the closest relative only among the groups/species/specimens that are included in the analysis.<ref>{{cite journal |last=Podani|first=János |title=Taxonomy in Evolutionary Perspective - An essay on the relationships between taxonomy and evolutionary theory |journal=Synbiologia Hungarica |year=2010 |volume=5 |pages=1–42 |url=https://www.scribd.com/doc/32972918/Podani-Taxonomy-in-evolutionary-perspective-Synbiol-Hung-6-1-42-2010}}</ref>

An example is [[birds]], whose commonly cited ''living'' sister group is the [[crocodilia|crocodiles]], but that is true only when discussing [[Neontology|extant organisms]];<ref>{{cite journal |author1=Padian, Kevin |author2=Lindberg, David R. |author3=Polly, Paul David |date=May 1994 |title=Cladistics and the fossil record: The uses of history |journal=Annual Review of Earth and Planetary Sciences |volume=22 |issue=1 |pages=63–89 |doi=10.1146/annurev.ea.22.050194.000431 |bibcode=1994AREPS..22...63P }}</ref><ref>{{cite journal |last=Kemp |first=T.S. |date=January 1988 |title=Haemothermia or Archosauria? The interrelationships of mammals, birds and crocodiles |journal=Zoological Journal of the Linnean Society |volume=92 |issue=1 |pages=67–104 |doi=10.1111/j.1096-3642.1988.tb01527.x}}</ref> when other, extinct groups are considered, the relationship between birds and crocodiles appears distant.
Although the bird family tree is rooted in the [[dinosaur]]s, there were a number of other, earlier groups, such as the [[pterosaur]]s, that branched off the line leading to the dinosaurs after the last common ancestor of [[archosaurs|birds and crocodiles]].<ref>{{cite news |last=Hughes |first=J.M. |date=2011-06-13 |title=Ancient bird-crocodilian ancestor uncovered |website=Aves Vitae - The lives of birds |url=http://www.avesvitae.org/www.avesvitae.org/News/Entries/2011/6/13_Ancient_Bird-Crocodilian_Ancestor_Uncovered.html |access-date=4 January 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120426091546/http://www.avesvitae.org/www.avesvitae.org/News/Entries/2011/6/13_Ancient_Bird-Crocodilian_Ancestor_Uncovered.html |archive-date=26 April 2012}}</ref>

The term ''sister group'' must thus be seen as a relative term, with the caveat that the sister group is only the closest relative among the groups/species/specimens that are included in the analysis.<ref>{{cite journal |last=Podani |first=János |year=2010 |title=Taxonomy in evolutionary perspective - An essay on the relationships between taxonomy and evolutionary theory |journal=Synbiologia Hungarica |volume=5 |pages=1–42 |url=https://www.scribd.com/doc/32972918/Podani-Taxonomy-in-evolutionary-perspective-Synbiol-Hung-6-1-42-2010}}</ref>

==Notes==
{{reflist|group=Note}}


== References ==
== References ==
{{Reflist}}
{{reflist|22em}}


{{Phylogenetics}}
{{Phylogenetics}}

Latest revision as of 05:17, 2 January 2025

In phylogenetics, a sister group or sister taxon, also called an adelphotaxon,[1] comprises the closest relative(s) of another given unit in an evolutionary tree.[2]

Definition

[edit]

The expression is most easily illustrated by a cladogram:

Sister group relationships

  Root  
  Subtree  
         

  Taxon A    

  Taxon B    

Clade
  AB
         

  Taxon C            

Clade
 ABC
         

  More tree branches  

Taxon A and taxon B are sister groups to each other. Taxa A and B, together with any other extant or extinct descendants of their most recent common ancestor (MRCA),[Note 1] form a monophyletic group, the clade AB. Clade AB and taxon C are also sister groups. Taxa A, B, and C, together with all other descendants of their MRCA form the clade ABC.

The whole clade ABC is itself a subtree of a larger tree which offers yet more sister group relationships, both among the leaves and among larger, more deeply rooted clades. The tree structure shown connects through its root to the rest of the universal tree of life.

In cladistic standards, taxa A, B, and C may represent specimens, species, genera, or any other taxonomic units. If A and B are at the same taxonomic level, terminology such as sister species or sister genera can be used.

Example

[edit]
A Dinosauria phylogeny including two extant taxa: birds (Theropoda) and crocodiles (Suchia).

The term sister group is used in phylogenetic analysis, however, only groups identified in the analysis are labeled as "sister groups".

An example is birds, whose commonly cited living sister group is the crocodiles, but that is true only when discussing extant organisms;[3][4] when other, extinct groups are considered, the relationship between birds and crocodiles appears distant. Although the bird family tree is rooted in the dinosaurs, there were a number of other, earlier groups, such as the pterosaurs, that branched off the line leading to the dinosaurs after the last common ancestor of birds and crocodiles.[5]

The term sister group must thus be seen as a relative term, with the caveat that the sister group is only the closest relative among the groups/species/specimens that are included in the analysis.[6]

Notes

[edit]
  1. ^ A tree diagram inevitably oversimplifies the complicated process of evolution.

References

[edit]
  1. ^ Ultrastructural evidence for an adelphotaxon (sister group) to the Neodermata (Platyhelminthes)
  2. ^ Eernisse, Douglas J. "Introduction to Phylogeny: What is a Sister Taxon?". Biology 404 - Evolution. Department of Biological Science, California State University, Fullerton. Retrieved 4 January 2012.
  3. ^ Padian, Kevin; Lindberg, David R.; Polly, Paul David (May 1994). "Cladistics and the fossil record: The uses of history". Annual Review of Earth and Planetary Sciences. 22 (1): 63–89. Bibcode:1994AREPS..22...63P. doi:10.1146/annurev.ea.22.050194.000431.
  4. ^ Kemp, T.S. (January 1988). "Haemothermia or Archosauria? The interrelationships of mammals, birds and crocodiles". Zoological Journal of the Linnean Society. 92 (1): 67–104. doi:10.1111/j.1096-3642.1988.tb01527.x.
  5. ^ Hughes, J.M. (2011-06-13). "Ancient bird-crocodilian ancestor uncovered". Aves Vitae - The lives of birds. Archived from the original on 26 April 2012. Retrieved 4 January 2012.
  6. ^ Podani, János (2010). "Taxonomy in evolutionary perspective - An essay on the relationships between taxonomy and evolutionary theory". Synbiologia Hungarica. 5: 1–42.
Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Sister_group&oldid=1266778657"