Evolución converxente: Diferenzas entre revisións

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! Estas dous xéneros de [[planta suculente|plantas suculentas]], ''[[Euphorbia]]'' e ''[[Astrophytum]]'', pertencen a liñaxes bastante afastadas en canto o seu parentesco, pero converxeron independentemente adoptando unha forma moi similar.

Convergent evolution is commonly noted when considering the morphology of animal species, but there are many diverse examples of the phenomenon in [[plant biology]] as well. A true [[fruit]] such as an apple incorporates one or more [[ovule]]s and their accessory tissues, but many edible plant-derived tissues commonly regarded as fruits actually arise from different embryological structures. This implies a convergent process in which genetically unrelated precursors assume a common form under selective pressure, in this case the competition for seed dispersal through consumption by animals.<ref name="evolution_seed">{{cite journal | author = Lorts C, Briggeman T, Sang T | title = Evolution of fruit types and seed dispersal: A phylogenetic and ecological snapshot | journal = Journal of Systematics and Evolution | volume = 46 | issue = 3 | pages = 396–404 | year = 2008 | doi = 10.3724/SP.J.1002.2008.08039 | url = http://www.plantsystematics.com/qikan/manage/wenzhang/jse08039.pdf}}</ref>

 

[[File:Evolutionary trends.svg|left|frame|Evolution at an [[amino acid]] position. In each case, the left-hand species changes from incorporating alanine (A) at a specific position within a protein in a hypothetical common ancestor deduced from comparison of sequences of several species, and now incorporates serine (S) in its present-day form. The right-hand species may undergo [[divergent evolution|divergent]], parallel, or convergent evolution at this amino acid position relative to that of the first species.]]

 

Similar to convergent evolution, evolutionary relay describes how independent species acquire similar characteristics through their evolution in similar ecosystems, but not at the same time ([[dorsal fin]]s of [[shark]]s and [[ichthyosaur]]s).

 

[[File:Beutelwolf fg01.jpg|upright|thumb|The skulls of the [[thylacine]] (left) and the [[gray wolf]] are quite similar, although the species are only distantly related. Studies show the skull shape of the [[red fox]] is even closer to that of the thylacine.<ref>{{cite journal|journal=Australian Journal of Zoology|volume=34|issue=2|year=1986|pages=109–117|title=Comparison of Skull Shape in Marsupial and Placental Carnivores|author=L Werdelin|doi=10.1071/ZO9860109}}</ref>]]

 

Convergence is difficult to quantify, so progress on this issue may require exploitation of engineering specifications (as of wing aerodynamics) and comparably rigorous measures of "very different course" in terms of phylogenetic (molecular) distances.

 

From a [[cladistic]] or [[phylogenetic]] point of view, homoplasious traits or changes (derived trait values acquired in unrelated organisms in parallel) can be compared with [[synapomorphy]] (a derived trait present in all members of a [[monophyletic]] [[clade]]), [[autapomorphy]] (derived trait present in only one member of a clade), or [[apomorphy|apomorphies]], derived traits acquired in all members of a monophyletic clade following divergence where the [[most recent common ancestor]] had the ''ancestral'' trait (the ancestral trait manifesting in [[paraphyletic]] species as a [[plesiomorphy]]).