Autapomorphy Explained

In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to the focal taxon (which may be a species, family or in general any clade).^[1] It can therefore be considered an apomorphy in relation to a single taxon.^[2] The word autapomorphy, introduced in 1950 by German entomologist Willi Hennig, is derived from the Greek words αὐτός, autos "self"; ἀπό, apo "away from"; and μορφή, morphḗ = "shape".^[3]

Discussion

Because autapomorphies are only present in a single taxon, they do not convey information about relationship. Therefore, autapomorphies are not useful to infer phylogenetic relationships. However, autapomorphy, like synapomorphy and plesiomorphy is a relative concept depending on the taxon in question. An autapomorphy at a given level may well be a synapomorphy at a less-inclusive level.^[4] An example of an autapomorphy can be described in modern snakes. Snakes have lost the two pairs of legs that characterize all of Tetrapoda, and the closest taxa to Ophidia – as well as their common ancestors – all have two pairs of legs. Therefore, the Ophidia taxon presents an autapomorphy with respect to its absence of legs.

The autapomorphic species concept is one of many methods that scientists might use to define and distinguish species from one another. This definition assigns species on the basis of amount of divergence associated with reproductive incompatibility, which is measured essentially by number of autapomorphies.^[5] This grouping method is often referred to as the "monophyletic species concept" or the "phylospecies" concept and was popularized by D.E. Rosen in 1979. Within this definition, a species is seen as "the least inclusive monophyletic group definable by at least one autapomorphy".^[6] While this model of speciation is useful in that it avoids non-monophyletic groupings, it has its criticisms as well. N.I. Platnick, for example, believes the autapomorphic species concept to be inadequate because it allows for the possibility of reproductive isolation and speciation while revoking the "species" status of the mother population. In other words, if a peripheral population breaks away and becomes reproductively isolated, it would conceivably need to develop at least one autapomorphy to be recognized as a different species. If this can happen without the larger mother population also developing a new autapomorphy, then the mother population cannot remain a species under the autapomorphic species concept: it would no longer have any apomorphies not also shared by the daughter species.^[7]

Phylogenetic similarities: These phylogenetic terms are used to describe different patterns of ancestral and derived character or trait states as stated in the above diagram in association with synapomorphies.

• Homoplasy in biological systematics is when a trait has been gained or lost independently in separate lineages during evolution. This convergent evolution leads to species independently sharing a trait that is different from the trait inferred to have been present in their common ancestor.^{[8] [9] [10]}
  • Parallel Homoplasy – derived trait present in two groups or species without a common ancestor due to convergent evolution.^[11]
  • Reverse Homoplasy – trait present in an ancestor but not in direct descendants that reappears in later descendants.^[12]
• Apomorphy  - a derived trait. Apomorphy shared by two or more taxa and inherited from a common ancestor is synapomorphy. Apomorphy unique to a given taxon is autapomorphy.^{[13] [14] [15] [16]}
  • Synapomorphy/Homology  - a derived trait that is found in some or all terminal groups of a clade, and inherited from a common ancestor, for which it was an autapomorphy (i.e., not present in its immediate ancestor).
  • Underlying synapomorphy  - a synapomorphy that has been lost again in many members of the clade. If lost in all but one, it can be hard to distinguish from an autapomorphy.
  • Autapomorphy – a distinctive derived trait that is unique to a given taxon or group.
• Symplesiomorphy  - an ancestral trait shared by two or more taxa.
  • Plesiomorphy  - a symplesiomorphy discussed in reference to a more derived state.
  • Pseudoplesiomorphy  - is a trait that cannot be identified as neither a plesiomorphy nor an apomorphy that is a reversal.^[17]
• Reversal  - is a loss of derived trait present in ancestor and the reestablishment of a plesiomorphic trait.
• Convergence  - independent evolution of a similar trait in two or more taxa.
• Hemiplasy^{[18] [19]}

Notes and References

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3. Book: Calow . Peter P. . vanc . Encyclopedia of Ecology and Environmental Management . 2009 . John Wiley & Sons . 978-1-4443-1324-6 . 1039167559 .
4. Book: Forey, Peter L. . vanc . History of the Coelacanth Fishes . Sprinter . 1st . 1997 .
5. Book: Howard . Daniel J. . Berlocher . Stewart H. . vanc . Endless Forms: Species and Speciation . Oxford University Press . USA . 1st . 1998 . 978-0-19-510901-6 . 60181901 . registration .
6. Book: Bull, Alan T. . vanc . Microbial Diversity and Bioprospecting . ASM Press . 2004 .
7. Web site: From Cladograms to Classifications: The Road to DePhylocode. . The Systematics Association . Platnick NI . 2001.
8. Web site: Similarity Happens! The Problem of Homoplasy . Ann . Gauger . vanc . April 17, 2012 . Evolution Today & Science News .
9. Book: Michael J. . Sanderson . Larry . Hufford . vanc . Homoplasy: The Recurrence of Similarity in Evolution . Elsevier . 21 October 1996 . 978-0-08-053411-4 . 173520205 .
10. Brandley MC, Warren DL, Leaché AD, McGuire JA . Homoplasy and clade support . Systematic Biology . 58 . 2 . 184–98 . April 2009 . 20525577 . 10.1093/sysbio/syp019 . free .
11. Archie . James W. . vanc . Homoplasy Excess Ratios: New Indices for Measuring Levels of Homoplasy in Phylogenetic Systematics and a Critique of the Consistency Index . Systematic Zoology . September 1989 . 38 . 3 . 253–269 . 10.2307/2992286 . 2992286.
12. Wake DB, Wake MH, Specht CD . Homoplasy: from detecting pattern to determining process and mechanism of evolution . Science . 331 . 6020 . 1032–5 . February 2011 . 21350170 . 10.1126/science.1188545 . 2011Sci...331.1032W . 26845473.
    • February 25, 2011 . Homoplasy: A good thread to pull to understand the evolutionary ball of yarn . ScienceDaily .
13. Book: Simpson, Michael G. . Plant Systematics . vanc . Amsterdam . Elsevier . 9 August 2011 . 9780080514048 .
14. Book: Peter J. . Russell . Paul E. . Hertz . Beverly . McMillan . vanc . Biology: The Dynamic Science . 978-1-285-41534-5 . Cengage Learning . 2013 .
15. Web site: Basics of Cladistic Analysis . Diana . Lipscomb . vanc . George Washington University . Washington D.C. . 1998.
16. Book: Choudhuri, Supratim . vanc . Bioinformatics for Beginners: Genes, Genomes, Molecular Evolution, Databases and Analytical Tools . 1st . Academic Press . 978-0-12-410471-6 . 950546876 . 51 . 2014-05-09 .
17. Book: David . Williams . Michael . Schmitt . Quentin . Wheeler . vanc . The Future of Phylogenetic Systematics: The Legacy of Willi Hennig . 978-1-107-11764-8 . 951563305 . 2016-07-21 .
18. Avise JC, Robinson TJ . Hemiplasy: a new term in the lexicon of phylogenetics . Systematic Biology . 57 . 3 . 503–7 . June 2008 . 18570042 . 10.1080/10635150802164587 . free .
19. Copetti D, Búrquez A, Bustamante E, Charboneau JL, Childs KL, Eguiarte LE, Lee S, Liu TL, McMahon MM, Whiteman NK, Wing RA, Wojciechowski MF, Sanderson MJ . 6 . Extensive gene tree discordance and hemiplasy shaped the genomes of North American columnar cacti . Proceedings of the National Academy of Sciences of the United States of America . 114 . 45 . 12003–12008 . November 2017 . 29078296 . 5692538 . 10.1073/pnas.1706367114 . free .