Autapomorphy

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In biology - especially in cladistics - an autapomorphy is a derived ( apomorphic ) trait that distinguishes a monophyletic group from related taxa. Derived means that the feature is new compared to the evolutionary predecessors. Both anatomical and physiological or direct genetic characteristics such as e.g. B. DNA sequences into consideration. The loss of a feature can also be assessed as an autapomorphism. Whether a feature is to be regarded as autapomorphism is the subject of evolutionary research and biological systematics .

The term autapomorphy depends on the considered level of the phylogenetic system. An autapomorphy as a derived feature of a taxon appears on the next lower level of the system as a synapomorphy of the two sister groups that make up this taxon. On the other hand, at even deeper levels, the agreement represents a symplesiomorphism .

Examples

human

Humans ( Homo sapiens ) and their closest extinct relatives (the Hominini ) can serve as an example . The hominini include the genera Ardipithecus , Australopithecus , Paranthropus, and Homo . Autapomorphies of this family are:

  • Lengthening of the rear extremities and transforming them into walking legs
  • Reshaping the rear feet by lengthening the metatarsals and shortening the toes
  • Redesign of the pelvis with the shape of the socket of the hip joint to accommodate larger loads
  • Conversion of the female pelvis in particular by enlarging the pelvic blades and the birth canal
  • Reshaping the hands of the front extremities into grasping organs (instead of climbing) by shortening the metacarpal bones

These anatomically recognizable features are related to the ability to walk and stand upright for long periods of time. They cannot be found in the other representatives of the superfamily of the human race (Hominoidea). Gibbons (Hylobatidae) are also able to walk upright over shorter distances, but they do not have the anatomical features listed above. Older fossils of monkeys, which are close relatives of the hominini's predecessors, do not show these characteristics either.

Tardigrade

All tardigrades (Tardigrada) have calcareous stilettos as mouth parts. The structure of all species of this animal strain is very similar, which means that they can be regarded as homologous to one another . While stilettos are also used in other animals such as insect larvae or nematodes before (Nematoda), but these stilettos differ both in the fine structure and in the development. Therefore, the tardigrade's specially built stilettos can be rated as autapomorphism.

Differentiation of analogies

When evaluating characteristics, it must be borne in mind that convergent evolution can create similar ( analogous ) organs, e.g. B. hem fins in squids (Theutida) and fish (Pisces) or the four-chambered heart in mammals (Mammalia) and birds (Aves). It is likely that a trait is autapomorphic of a taxon if it is homologous within the taxon and does not appear in any closely related groups . The probability of homology increases with the complexity of the feature.

However, an autapomorphism can also be the lack of a feature. If there are missing features, the assessment of homology is logically not possible because only existing features can be compared.

Related topics

swell

  1. ^ W. Hennig (1982): Phylogenetic Systematics. Paul Parey Publishing House, Berlin. P. 94.
  2. ↑ P. Ax (1988): Systematics in Biology. Gustav Fischer Verlag, Stuttgart. P. 69ff.
  3. ↑ B. Wood & N. Lonergan (2008): The hominin fossil record: taxa, grades and clades. In: Journal of Anatomy , Volume 212, No. 4. pp. 354–376, DOI: 10.1111 / j.1469-7580.2008.00871.x , PDF online ( Memento from October 20, 2012 in the Internet Archive )
  4. ^ P. Ax (1999): The system of the Metazoa II. Gustav Fischer Verlag, Stuttgart. P. 354.
  5. ^ W. Sudhaus & K. Rehfeld (1992): Introduction to Phylogenetics and Systematics. Gustav Fischer Verlag, Stuttgart. P. 116f.