Pluralism of concepts: the PCS

D.F.Silva

There are three basic concepts phylospecies. one of them, initially defined by Hennig, is the Henniano species concept (Meier & Willmann 2000). Henniana convention: if new species arise from division from a parent species, then I would say the parental species is not monophyletic (now paraphyletic), has been lost and now there are two new species. The second concept is called phylospecie Concept synapomorphic. A species is one in which no beyond there taxonomic division or subdivision is the phylogenetic analysis unit. The version of Mishler adds it on this concept, the vision of that species should be monophyletic. The phylospecie third concept of the so-called Autopomorphyic concept, according to one version of Wilkins. The concept is called diagnosis. this concept is derived from the work tends to Rosen.este rely on the diagnosis of taxa or is a completely epistemological notion of species. All concepts that rely on autapomorficos species is the terminal taxon in a cladogram.

Hennig is often read as: species cease to exist when they are divided bone when relationships end hologenetics be a simple set. hennig but assumes that species are reproductive communities genes harmonic butler, as he had said Dobzhansky, and that species are reproductive groups as Mayr said, however hennig assumes that species are reproductive lineages. but the most important aspect of the definition lies in the dimencion hennig time where the note that species have to be bounded by speciation event "The limits of the species in a longitudinal section through time could therefore be determined by two processes of speciation: one which rise as an independent reproductive community and one which travez the descendants of these initial populations ceased to exist as one homogeneous reproductive community. When some of the relationships between individuals tokogenetics of a species no longer exist, that breaks into two species and ceases to exist.

The criticisms have not been expected and appeared to be a delineation somewhat arbitrary to species taxa. this has come to call Hennig convention. the Hennig the concept of the species has been expanded by Meier & Willmann. hennnig proposed a modified concept: species are natural populations reproductively isolated groups of wild populations. they originate by way of the dissolution of the stem species of speciation events and cease to exist travez of speciation or extinction. hennig basically the concept of species is a concept of biomolecules as has hennig accepted that reproductively isolated species were exposed and that the criteria used identifying relevant edges of the clades are phylogenetic simply those of biospecies or BCS. The extinction is a taxonomic extinction.

Synapomorphic species

The Concept is special because although Brent Mishler has defined Cracraft the species taxon as the smallest diagnosable cluster organisms within which there is a pattern of ancestry or descent. Mishler and monophyletic version: a species is the most inclusive taxon recognized in a classification into which organisms are grouped together because evidence of monophyly (usually, but not restricted to the presence of synapomorphies) such that it is positioned as a species because it is the smallest lineage important. and redefine monophyly: A monophyletic taxon is a group that contains all and only descended from a common ancestor originandoce in the same event.

Synapomorphic species are usually based on historical lines ancestry current offspring that are represented in a cladogram. as a phylogenetic taxon species is a synapomorphy shared by agupada for individuals that show monophyly .The definition of Mishler and Theriot: a species is the most inclusive taxon recognized in a formal phylogenetic classification. As with all levels levels of taxa in such classifications grouped organisms within species because of evidence of monophyly. taxa are classified as species because they are the groups phylogenetic smaller. monophyletic conception here is explicit. dual nature of the epistemic and the ontological aspects are expressed notably marked and the range of species lineages is restricted to biologically important. De Queiroz and Donoghue [1988, 1990] do not think that species have to be monophyletic because the monophyly of the populations does not provide a way to specify which is the basis of the range.

Autapomorphyc Species or diagnostic.

Diagnosis of the species has been embroiled in a debate. species have diagnostic autapomorphies whereas higher taxa are synapomorphies Rosen noticed that the subspecies are by definition unobservable and indefinable. since they have no apomorphies. Nelson and Platnick tratarona species as shows just the smallest of organisms detected own perpetuation that have unique set of character . (Wheeler & Platnick 2000; 56) Almost contemporaneously Eldredge & cracaraft defined a species as a diagnosable cluster of individuals who within which there is a pattern of ancestry and descent.

PHYLOGENETIC SPECIES CONCEPT

Jiménez- Silva C. L.

The ratings are the historical framework for interpreting the patterns of similarities between taxa, ecological interactions and their geographic distribution (Brooks, 1981; Cracraft, 1983; Eldredge and Cracraft, 1980; Farris, 1979) The species has been considered the foundation in construction of classifications of the trees evolutivos.Las different versions of the phylogenetic species concept is characterized by accepting the evolutionary and biological conception and to delimit the species in one way or another. Hennig defined the species as "groups of individuals who are interconnected by tocogèneticas relations are called species (Hennig 1996). Then Hennig believed that: "The species should then be defined as a complex of spatially distributed reproductive communities, or if we call this relationship in the" vicariance "as a vicariant complex communities of reproduction" (Hennig 1966)

The species can be considered a species level, among all those available in the hierarhy filogenética. 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 and Mishler, 1996). The phylogeny or the search for parsimonious cladograms formal and robust only to discover monophyletic groups and build a classification according to Mishler. Mishler and Donoghue (1982) also split two operational aspects of species recognition. First, agencies may be grouped into species based over monofilesis evidence (autopomorphies), as is the case in the 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, ie, they vary in different organisms. Theriot is, agree to the taxa at the species level should be distinguished by discrete apomorphic states rather than by total or plesiomorphic similarity (Theriot, 1992).

Other authors such as Wiley says, "An evolutionary species is a single lineage of ancestral-descendant populations which maintains its identity from other lineages and have their own evolutionary tendencies and historical fate" (Wiley 1978). In this case the species is formed by organsmos evolve independently, while maintaining the identity to other lineages, which is maintained through relations that are generated lattice throught mating among similar organizations. From this it follows that the species is well defined independent biological units to be guided by evolution and that holds it together through reproduction (De Haro 1999)

Cacraft states that a species diagnosable smaller group of individual organisms in which there is a pattern of parental ancestor descendant (Cacraft 1983). To this author is an indispensable part of the definition to diagnose the species in question. For some like De Haro (1999) this is beyond the interest of the dynamics of the process since we are not able to diagnose the species exist and our limitations do not affect the process.



The phylogenetic species concept as Nixon and Wheeler: "the smallest aggregation of populations (sexual) or lineages, (asexual) diagnosable by a unique combination of character states in comparable individuals (semaforontes)" (Nixon and Wheller 1990). This definition of species differs little from the Cacraft in depth, but it is operationally more precise phylogenetic studies, which are those that may eventually shed light on these patterns of segregation and on the basis of which should be the separation of the species and is the grouping of these terminals evolving information which may eventually define a more precise and natural supraspecific categories. This definition creates a working tool for the detection of minimal terminals for phylogenetic analysis (Davis and Nixon 1992). Species are groups of organisms that evolve together and are able to maintain its own identity distinct from grups. These other species are different because they have diverged evolutionarily and not because they are different according to the human eye.


Haro, J.J. 1999. ¿Qué es una especie?.Bol. S.E.A. 26:105-112

Nixon, K. C., and Q. D. Wheeler. 1990. An amplification of the phylogenetic species concept. Cladistics 6:211±223

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

Hennig, W. 1966. Phylogenetic systematics. Urbana, IL: University of Illinois Press.

Wiley, E. O.,1978. The evolutionary species concept reconsideres. Syst. Zool., 27: 17-26.

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

Phylogenetic Species Concept

Gualdrón-Diaz J. C.

Several Phylogenetic Species Concept have been proposed. The first in applied cladistic methods to the species problem was Rosen (1978), who defined species as "a geographically constrained group of individuals with some unique apomorphous characters, is the unique evolutionary significance", after de Queiroz and Donogue (1988) argued that species should be based on monophyly and the grouping of populations supported on sinapomorphies. Although an ancestor must have existed ans must have been a species in its own time, an ancestral species according to phylogenetic theory has no autapomorphies in relation to their own descendant species (Wheeler 1999). According to this concept of the species are defined from the point of view phenotype, the level of state support monophyletic, nevertheless sometimes there is no evidence on monophyletic status of a group.

Also, Eldredge and Cracraft (1980) and Nelson and Platnick (1981) proposed similar species definitions, later amplified by Nixon and Wheeler (1990) and Wheeler and Platnick (2000); All based on defining species a unique combination of diagnosable characters; moreover, some of these concepts have in mind a pattern in the ancestor-descendant. Nevertheless this approach does emphasis in the capacity that is had to distinguish to a species of other one, which is a problem of the taxonomist and of the systematic one, which does not concern the existing organism in the nature (Haro 1999).

In spite of the different concepts proposed with relation to the phylogeny, the goal for developing a phylogenetic species concepts is to support the aims of phylogenetics systematics as the elements for reconstruction of phylogenetic history, distinguish among kinds of organisms, describe and predictively classify the diversity biological, and permit the study of evolution and comparison of clades (Wheeler and Platnick 2000).

References

Eldredge, N., and J. Cracraft. 1980. Phylogenetic patterns and the evolutionary process. New York: Columbia University Press.

Haro, J.J. 1999. ¿Qué es una especie?.Bol. S.E.A. 26:105-112

Nelson, G., and N. I. Platnick. 1981. Systematics and biogeography: Cladistics and vicariance. New York: Columbia University Press.

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.

Wheeler, Q. D. 1999. Why the phylogenetic species concept? -elementary. Journal of Nematology 31:13–141.

Wheeler, Q. D., and Platnick, N. I. 2000. A critique from the Wheeler and Platnick Phylogenetic Species Concept Perspective: Problems with Alternative Concepts of Species. In: Species Concepts and Phylogenetic Theory (Ed. Q. D. Wheeler and R. Meier), pp. 133-145, Columbia University Press, New York.

de Queiroz, K., and M. J. Donogue. 1988. Phylogenetic systematics and the species problem. Cladistics 4:317-338.

An approach from phylogenetic species concept

Susan@ Ortiz B.

Even though the species concept is an important topic in the recognition and conservation of biological diversity, presently there are no a universal concept and choosing one in particular is controversial in all cases. Perhaps, just like Wheeler (1999) mentioned, there are more species concepts in use today than any other time; however, the Phylogenetics Species Concept (PSC) could be considered a good approach. According to cladistic principles, the PSC suggested by Rosen (1978), is focused to population or group of populations geographically constrained defined by one on more unique apomorphous features. After a decade, a modified version was proposed by Queiroz and Donoghue (1988), as the smallest unit determined cladistically at least one specific character. Evidently, this concept is based on autapomorphic background and therefore the species are defined under monophyly criterion. However, some practical difficulties arise about recognition of ancestral species based on autapomorphies, since, the character becomes a synapomorphy and the ancestral taxon actually differs from its descendant due to lack of the evolutionary novelty. Additionally the PSC point out against BSC the absence of reproductive isolation as a plesiomorphic character inappropriate in the delimitation of species (Wheeler and Meier, 2000) and the absence of reproductive boundaries between ancestral and descendant populations (Hennig, 1966).

On the other hand, Eldredge and Cracraft (1980) and Cracraft (1983) addressed the PSC towards diagnosable characters, establishing the specie as a diagnosable cluster or the smallest diagnosable cluster of individuals within which there is a parental pattern of ancestry and descent. Afterwards Nelson and Wheeler (1990) redefine it as the smallest aggregation of populations or lineages diagnosable by a unique combination of character states. As well this concept also is based on the relationships between species and its characters, although not necessarily imply monophyly, being that the autapomorphic characters are diagnosable, but no all diagnosable characters can be autapomorphies. This approach seems to evoke the Typological Species Concept with regard to constant diagnostic differences to identify species (Mayr, 1991); nonetheless the measure is less arbitrary because it follows a parental pattern of ancestry and descent. A critique against this concept indicates that the species exist in nature independently of the systematic’s ability to diagnose them (Haro, 1999). Obviously, diagnosable apomorphies must be sought, but this is a systematic’s problem that does not affect the organism as real entity. Another difficulty is to define the boundaries of diagnostic in polytypic species with a wide variety, which could lead to false increases in diversity and underestimation of intraspecific variation (Fernandez et al., 1995).

Despite the above, the PSC is an operational concept compatible with phylogenetic theory designed to recognize and define the groups for any characteristic, from morphological to molecular. Some fundamental components of the PSC are the weighting of the recognition against reproductive isolation and lack of a temporal dimension under BSC (Willmann and Meier, 2000), its applicability to all evolving systems, whether sexual or asexual (Balakrishnan, 2005) and the recognition that species based on observable, testable characters simply avoid the confusion imparted by considerations of modes of speciation (Wheeler, 1999). Likewise, according to Balakrishnan (2005) the major practical troubles include determining whether shared traits have attained fixation in the population (Wiens and Servedio, 2000), determining how many diagnostic traits to consider and the inapplicability of this approach to most continuously varying quantitative traits (Willmann and Meier, 2000). Finally, although PSC has not completely solved the conflict between the real species existing in nature and the criteria and tool to recognize, it constitutes an attractive approach and a step in this direction. Also emphasize the diversity of mechanisms that can give rise to real species in nature and that are not all recognized by the BSC.

References

Balakrishnan, R. 2005. Species Concepts, Species Boundaries and Species Identification: A View from the Tropics. Syst Biol.2005; 54: 689 -693.

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

Eldredge, N., and J. Cracraft. 1980. Phylogenetic patterns and the evolutionary process. New York: Columbia University Press.

Fernández, F., Hoyos J. M. and D. R. Miranda. 1995. Especie. Innovacion y Ciencia. 32-37.

Haro, J.J. 1999. ¿Qué es una especie?.Bol. S.E.A. 26:105-112

Hennig, W. 1966. Phylogenetic systematics. Urbana, IL: University of Illinois Press.

Mayr , E. 1991. One long, argument, Charles Darwin and the genesis of modern evolutionary thought. Harvard University Press, Cambridge, Mass.

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.

Wheeler, Q. D. 1999. Why the phylogenetic species concept? -elementary. Journal of Nematology 31:13–141.

Wheeler, Q. D., and R. Meier. 2000. Species Concepts and Phylogenetic Theory. Columbia University Press, New York. pp. 133-145.

Willmann, R., and R. Meier. 2000. A critique from the Hennigian Species Concept Perspective. In: Species Concepts and Phylogenetic Theory (Ed. Q. D. Wheeler and R. Meier), pp. 101-108, Columbia University Press, New York.

de Queiroz, K., and M. J. Donogue. 1988. Phylogenetic systematics and the species problem. Cladistics 4:317±338.