martes, 31 de agosto de 2010

SPECIES CONCEPT.

Jiménez- Silva C. L.


A specie is the smallest diagnosable group identified as an ancestor-descendant populations evolving separately from others (Cacraft, 1983).The species is diagnosable by a unique combination of characters to compare individuals who achieve this identity is owned by the agency and not the investigator.

The actual existence of the species gives genealogical relationships with other group of organisms, their historical behavior, so it is considered that the species are different because they have diverged evolutionarily. Wiley (1978) supports this assertion by suggesting that the species is a single lineage of ancestral-descendant populations, they retain their identity from other lineages and have their own evolutionary tendencies and historical fate. A realistic notion of species derived from its interactions with the environment and other species (Mayr, 1942).

The species is monophyletic given that can be considered as a species level, among all that exist in the phylogenetic hierarchy. Only monophyletic groups can be recognized and formally named taxa.This principle is based on the groups which include all the descendants of a single common ancestor are the only groups with real and natural existence in relation to the evolutionary process (De Luna & Mishler, 1996).The phylogeny, or search for parsimonious cladograms is the only formal and robust procedure to discover monophyletic groups and build a classification according to Mishler.

The species concept of Rosen (1978.1979) states that the basis for grouping the cladistic system is synapomorphies. A monophyletic group consists of a cross section of a race and only includes members coexisting at the time (Sober, 1998). Empirically synapomorphies are known for, as these are the only evidence of recent common ancestry.Taxa at the species level, must also be distinguished by discrete apomorphic states rather than by total or plesiomorphic similarity (Theriot, 1992).According to Mishler and Donoghue (1982) separated two operational aspects of species recognition. First, agencies may be grouped into species on the basis of evidence monofilesis (autopomorphies), as is the case in other taxonomic levels. The criteria for crossover in particular should not be used for purposes of grouping. Second, the criteria to assign species status to certain monophyletic groups should be pluralistic, they vary in different organisms.

In the biological species concept, according to Mayr (1963) states: "Species are groups of interbreeding natural populations that are reproductively isolated themselves from other groups", I don´t consider it appropriate because it does not provide mechanisms for the recognition of species( Sneath & Sokal, 1973),applies only to individuals with sexual reproduction, it doesn´t solve the problems of parthenogenetic forms groups or developmental stages of a simple line.(Coyne et al., 2004); Furthermore, the similarity does not indicate reproductive membership in the same lineage or monophyletic group, since the ability to interbreed is a plesiomorphic often.( Bremer y Wanntorp, 1979; Donoghe, 1985; Rosen, 1979).

Over the genealogical history, phylogenetic species concept Biological has no clear meaning, for example: itself a kind A, extinct, resulting in two species: B and C by cladogenesis, then you can apply the biological species concept to the stem species to extinction of A makes it meaningless words "that are reproductively isolated from other groups".

In conclusion the concept of species must be based on a real group, Diagnosable, ancestor-descendant populations evolving separately from others, is monophyletic are recognized by discrete synapomorphies and apomorphic states instead of all or plesiomorphic similarity.

References

Bremer, K. & Wanntorp, H.-E. 1979. Hierarchy and reticulation in systematics. Systematic Zoology 28: 624—627.

Cracraft, J. 1983. Species concepts and speciation analysis. Current Ornithology, 1, 159–187.

Coyne, J.A. & Orr, H.A. 2004. Speciation. Sinauer Associates, Inc. Sunderland, Massachussets.

de Queiroz, K., and M. J. Donogue. 1988. Phylogenetic systematics and the species problem. Cladistics 4:317±338.
Haro, J.J. 1999. ¿Qué es una especie?.Bol. S.E.A. 26:105-112

Mayr, E. 1942. Systematics and the Origin of Species from the Viewpoint of a Zoologist. Columbia University Press: New York.

Mayr, E. 1963. Animal species and evolution. Cambridge: Belknap Press of Harvard University Press.

Mishler, B. D., and E. de luna. 1997 Sistemática Filogenética y el concepto de especie.Bol. Soc. Bot. México 60: 45-57

Mishler, B.D. & M.J. Donoghue. 1982. Species concepts: a case for pluralism. Systematic Zoology 31: 491-503.

Nixon, K. C., and Q. D. Wheeler. 1990. An amplification of the phylogenetic species concept. Cladistics 6:211±223
Rosen, D. E. 1978. Vicariant patterns and historical explanation in biogeography. Systematic Zoology 27: 159±188.
Sokal, R.R. & Rohlf, F.J. 1966. Random scanning of taxonomic characters. Nature 210: 461-462
Theriot, E. 1992. Clusters, species concepts and morphological evolution of diatoms. Systematic Biology 41:141-157.
Wiley, E. O.,1978. The evolutionary species concept reconsideres. Syst. Zool., 27: 17-26.