Apomorphism

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Apomorphy (from ancient Greek από apo "from, away" and μορφή morphē "form, shape") is a fundamental concept of cladistics (method of biological systematics ). It contains a newly acquired (“progressive”, “derived” ) characteristic in the course of the phylogenesis of a taxon . The corresponding adjective for such a feature is apomorphic . In contrast, there is plesiomorphism , the original (“primitive”) feature. All of these concepts and names go back to the German entomologist and founder of cladistics Willi Hennig .

Sub-terms

Simple example cladogram with description of the characteristics. Features 3 to 6 are each autapomorphies of the four terminal taxa A to D. Features 1 and 2 are each autapomorphism of clades A + B and C + D and at the same time synapomorphies of terminal taxa A and B or C and D. Note, that for the topology (the shape of the branches) only the two synapomorphies are decisive. The four autapomorphies of the terminal taxa are uninformative in this regard .
In the event that the terminal taxa A and B each had a sister group (A ′ and B ′), which also each had characteristic 1, this characteristic would be plesiomorphic for the four terminal taxa A to B ′.

Depending on whether the characteristics of an individual taxon are compared to other taxa or the common characteristics of the subtaxa of a taxon are compared, one speaks of either autapomorphies or synapomorphies :

  • An autapomorphism is an apomorphic feature that appears in the basic pattern of a species * or a (more inclusive) monophyletic taxon and distinguishes this taxon from other taxa. Autapomorphies are therefore essential for the identification and description of newly discovered taxa.
  • A synapomorphism is the common appearance of an apomorphic trait in directly related taxa that they inherited from their most recent common ancestor . The term synapomorphism thus forms at least an intersection with the term homology . Synapomorphies therefore establish a sister group relationship and are therefore essential for the determination of phylogenetic hypotheses (mostly visualized by cladograms ) in cladistics.

Which of the two terms is to be used for a characteristic in a specific case, autapomorphism or synapomorphism , depends on whether the delimiting character of the characteristic of an individual taxon or the unifying character of this characteristic is to be emphasized on the next more exclusive hierarchical level: hair is an autapomorphy of the taxon mammals , but in a comparison of the two main lines of mammals, hair is a synapomorphism of the taxa monotones and theria ( marsupials + placentas ).

The concept of apomorphism is relative to a similar extent, because the autapomorphy at the base of a clade has the character of a (sym-) plesiomorphism within the less inclusive clades it contains, i.e. H. the hairs, which are autapomorphic at the base of the mammals, are (sym-) plesiomorphic in the subgroups of the Theria. This also means that symplesiomorphies are also homologous, although they do not go back to the most recent common ancestor.

*In cladistics, a distinction is sometimes made between species and monophyletic taxa on the basis of the concept of the (inevitably paraphyletic ) parent species.

Examples

Note that higher ranking taxa in particular are often named after their apomorphism or one of their most striking apomorphisms.

  • The possession of mammary glands in the chest and abdomen is a common characteristic of all mammals , which distinguishes them from the rest of the terrestrial vertebrates ( amphibians , reptiles and birds ).
  • The flowering plants (angiosperms) differ from the other seed plants by the transformation of the female reproductive system to a carpel (carpel) containing the ovules and the pollen receives for fertilization.
  • The apomorphic characteristic of the flying insects (pterygota) consists in the presence of veined wings that are attached to the thoracic segments .
  • The loss of structures ( "negative feature") can be a apomorphy: So is in the slugs , the housing completely regressed. However, negative traits alone are unsuitable to justify taxa, as it is more likely that reductions occur independently of one another in different lines of development than that identical complex structures arise independently of one another ( convergent ) in different lines of development. In fact, a comparison of additional and “positive” features shows that the reduction in the shell of the slugs cannot be a synapomorphism of a monophyletic group, but has occurred several times in different lines of the slugs.

See also

Web links

  • Apomorphy in the spectrum Online lexicon of biology

Individual evidence

  1. ^ Stefan Richter, Rudolf Meier: The development of phylogenetic concepts in Hennig's early theoretical publications (1947–1966). Systematic Biology. Vol. 43, No. 2, 1994, pp. 212-221, doi: 10.2307 / 2413462 (alternative full-text access : ResearchGate )
  2. ^ Mario GG de Pinna: Concepts and tests of homology in the cladistic paradigm. Cladistics. Vol. 7, No. 6, 1991, pp. 367-394, doi: 10.1111 / j.1096-0031.1991.tb00045.x (alternative full text access : CiteSeer X ), p. 369 ff.
  3. ↑ a b c Olivier Rieppel: Introduction to computer-aided cladistics. Pfeil, Munich 1999, ISBN 3-931516-57-1 , p. 30 f.
  4. ^ John S. Wilkins: Species: A History of the Idea. University of California Press, 2009, ISBN 978-0-520-26085-6 , p. 206