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.

Phylogenetic Species Concepts: Diagnosable Version

Gualdrón-Diaz J. C.

Since of need individual for different researchers, have been development at least 22 concepts of species to characterize diversity, some of these researchers have been motivated by operational or empirical definitions, others by theoretical necessity, while some encouraged by peculiarities of organisms studied (Mayden 1997). However, all the concepts to present problems and disadvantage, some more than others, many of these are notably incompatible in the accounts the diversity and not all concepts have been equally well characterized or explicitly defined (Mayden 1997). Despite this, all attempts to define species depending on the needs and interests of each.

Of all the concepts raised, I agree with the definition of phylogenetic species. The phylogenetic species concept (PSC) has its origin in the writing of Willi Hennig (1966) and subsequent transformations of phylogenetic theory. Hennig recognized that the Biological Species Concept (Mayr, 1942-1963) was problematic with relative to the chronological history of species and proposed modifications designed to fix this species concept.

Several positive aspects of the PSC make them particurly attractive as operations in discovering biodiversity, and resolving some of the perceived problems with other concepts (Mayden and Wood, 1995). Currently at least three different concepts of species are identified as phylogenetic.The different PSCs form three general classes; one emphasizing monophyly, one emphasizing diagnosable, and one emphasizing both (Mayden 1997).

I concur with the diagnosable version of phylogenetic species concept, which have been proposed by several authors who defined the species as: “...a diagnosable cluster of individuals within which there is a parental pattern of ancestry and descent, beyond which there is not, and which exhibits a pattern of phylogenetic ancestry and descent among units of like kind” (Eldredge and Cracraft, 1980); ...”the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent”(Cracraft, 1983); “...simply the smallest detected samples of self perpetuating organisms that have sets of characters” (Nelson and Platnick, 1981); “...the smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals (semaphoronts)” (Nixon and Wheeler, 1990; Wheeler and Platnick, 2000).

This definition emphasizes that a priori species are diagnosable regardless of a criterion of monophyly. Although the correspondence between characters, homologs, and apomorphies is of critical importance to cladistics (Patterson 1985), such distinctions are irrelevant to species recognition. In this sense, this concept differs from other proposed phylogenetic concepts, which require identification apomorphies to diagnose species; According to this, those not possesing autapomorphic attributes do no constitute a species.The monophyly, for proponents of this concept, apply only at a level of organization above species. Species are delimited by the distributions of fixed, diagnostic characters across populations (Mayden 1997) and there is no inherently arbitrary divergence or distinction between species or subspecies in a polytypic species (Cracraft, 1983, Warren, 1992). subspecies have no ontological status.

The positive aspects to this concept over others are: First, process is not invoked before patters is observed, to initially distinguish species, this do so in preparation for and prior to a cladistic analysis (Wheeler and Platnick, 2000). Second, phylogenetic methodologies are argued to be applicable only to genealogical relationships of species and supraspecific taxa, not below the level of integration of species wherein tokogenetic relationships of infraspecific entities are the norm (Wheeler and Nixon, 1990; Nixon and Wheeler, 1990).

Finally, this concept also have the ability to recognize both biparental and uniparental species, and possess no implied modes of selection nor speciation, besides it is more compatible with phylogenetic theory because speciation events are marked by character transformations (Mayden 1997, Wheeler and Platnick, 2000).

References

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.

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

Mayden, R. L., and R. M. Wood. 1995. Systematics, Species Concepts, and the Evolutionarily Signficant Unit in Biodiversity and Conservation Biology. Special Publication, American Fisheries Society, Bethesda, Maryland. (No. 17: 58-113).

Mayden, R. L. 1997. A hierarchy of species concepts: the denouement in the saga of the species problem. In Species:The units of biodiversity. Edited by M. F. Claridge, H. A. Dawah, and M. R. Wilson. London: Chapman & Hall. pp. 381-424.

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.

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

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

Paterson, H. 1985. The recognition concept of species. Pp. 21-29 in E. Vrba, ed. Species and speciation. Transvaal Museum, Pretoria.

Warren, M. L., 1992. Variation of the spotted sunfish, Lepomis punctatus complex (Centrarchidae): meristics, morphometrics, pigmentation and species limits. Bull. Ala. Mus. Nat. Hist. 12:1-47.

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.

Who is Right?

Susana Ortiz B.

Although it is true the species concept has been controversial and approached from multiple perspectives throughout history, its applicability and acceptance depends on how well to recognize, identify and understand the species in nature hence its relevance in areas like conservation, ecology, evolution, taxonomy and of course systematic. The Biological Species Concept (BSC) is perhaps the most widely accepted species concept in biology, it defines species in terms of interbreeding and reproductive isolation (Mayr, 1963). This lats feature based on barriers to gene flow between populations includes not only geographic isolation but also prezygotic factors such mate choice, and fertilization incompatibilities and postzygotic factors i.e., hybrid inviability and sterility caused by genomic incompatibilities (Dobzhansky, 1937). However, in practice this concept involves some difficulties mainly in relation to hybridization, asexual populations, adimensionality and not distinction between reproductive isolation and the speciation´s process (Mallet, 2007; Fernandez et al., 1994; Templeton, 1989).

In view of this scenario, emerges the Phylogenetic Species Concept (PSC), which stablishes the recognition as criterion for species delimitation through characters; despite the multiple versions, the PSC proposed by Eldredge and Cracaft (1980) and later rephrased by Cracraft (1983) conceives the specie as “…the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent”, the above entails some operational advantages, such as its applicability to fossils and all evolving systems of living things whether sexual and asexual populations and you do not need to know or understand the process driving speciation in order to recognize species (Claridge et al. 1997; Nelson and Placnick, 1981) . Under this concept the pattern of characters distribution in nature provides testable evidence of the existence of species in nature (Wheeler, 1999), additionally it seems to return to typological species concept given its confinement to diagnostic characters, nonetheless, the PSC emphasizes the relationship between unique combination of inherited characters either molecular or morphological and an ancestral–descendant sequence.

According to Cracraft (1989), species defined under this diagnostic criterion are real taxa suitable for phylogenetic analysis and evolutionary studies, being so is necessary to take special care of strict application rather in small groups and polymorphic species if unknown genetics aspects, geographic distribution and demography of the group, this in order to avoid underestimating the intraspecific variation and therefore the wrong multiplication of species (Mallet, 2007; Fernadez et al., 1995); However, to counteract such diagnosable groups have no authentic parental pattern of ancestry and descent (Cracraft, 1989). Another relevant aspect of the diagnostic species concept is the fundament of this diagnosticability that is the characters as synapomorphies or autapomorphies or simply characters as descriptors indistinctly of their historical background. This latest maybe is the most permissive given that it has not conflict in to recognize cladogenesis or anagenesis indistinctly and can be monophyletic or non-monophyletic. On this basis, also the concept is ambiguous because it could behave like synapomorphy, autapomorphy or simplesiomorphy in the same branch, also the major practical difficulties include determining whether shared traits have attained fixation in the population (Wiens and Servedio, 2000) and the inapplicability of this approach to most continuously varying quantitative traits (Willmann and Meier, 2000).

The monophyly criterion of species is an important component in synapomorphic and autapomorphic versions of the PSC, thus, they do not recognize the phyletic change or anagenesis, just the cladogenesis as evolutionary process. Following the above, in cladogenesis from a stem species, subspecies may first appear and then a new species with acquisition of apomorphies, nevertheless, the autapomorphic concept could recognize subspecies as species before the consolidation of the cladogenesis (De Haro, 2005); other problem is that it excludes the existence of stem-species by definition, since these can neither be monophyletic, nor can they possess autapomorphies, relative to its own descendant species since they inherit their "autapomorphies", so that the former autapomorphies of the stem-species become the autapomorphies of the resulting monophylum and thus become symplesiomorphies of the stem-species (Wheeler, 1999; Wheeler and Meier, 2000). On the other hand, the PSC based on synapomorphy, addresses the species problem from a perspective different, perhaps this is synapomorphy and monophyly in terms of relations among species and their characters (Hennig, 1966), but at this level should reflect the branching, or cladistic, relationships among species (Goldstein and De Salle, 2000), ie, the synapomoraphies may show the phylogenetic relationships of two or more species belong to a monophyletic group, then take this group as a single species is inadequate and even more when the historical status may be unresolved. Maybe, monophyly is an ambiguous concept whose problem lies a fundamental distinction between species and monophyletic taxa, where species form mutually exclusive reticulated systems, while higher taxa form inclusive hierarchical systems (Rieppel, 2009).

Finally, although in many contexts the PSC emphasizes a diversity of mechanisms that can give rise to real species in nature and that are not all recognized by the BSC (Claridge et al. 1997), operational difficulties exist for the identification of distinct historical entities in nature regardless of the phylogenetic species concept applied (Frost and Kluge, 1995), however, seems that the most adequate species concept is perhaps the autapomorphic concept in despite of its difficulties, without this meaning that it is the right or the universal criteria by which species may be delimited, it is just a good approximation to define and recognize the diversity of life.

References

Claridge, M. F., H.A. Dawah, and M. R.Wilson. 1997a. Practical approaches to species concepts for living organisms. Pp. 1–15 in Species: The units of biodiversity. Edited by M. F. Claridge, H. A. Dawah, and M. R. Wilson. London: Chapman & Hall.

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

Cracraft, J. (1989). Speciation and its ontology: The empirical consequences of alternative species concepts for understanding patterns and processes of differentiation. In Speciation and its Consequences (D. Otte and J. A. Endler, Eds.), pp. 28–59. Sinauer Associates, Sunderland, MA

Dobzhansky, T. 1937. “Genetics and the Origin of Species.” Columbia Carpenter, J. M. (1992). Random cladistics. Cladistics 8, 147–153.

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

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

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Murphy, F. A., C. M. Fauquet, D. H. L. Bishop, S. A. Ghabrial, A. W. Jarvis, G. P. Martelli, M. A. Mayo, and M. D. Summers (ed.). 1995. Virus taxonomy: classification and nomenclature of virus, p. 415±421. Spring-Verlag, New York, N.Y.

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

Rieppel, O. 2009. Species monophyly. Journal of Zoological Systematics and Evolutionary Research. 48 (1), 1-8.

Templeton, A. R. 1989. The meaning of species and speciation: A genetic perspective. In “Speciation and Its Consequences” (D. Otte and J. A. Endler, Eds.), pp. 3–27. Sinauer Associates, Sunderland, MA.

Van Regenmortel, M. H. V. 1990. Virus species, a much overlooked but essential concept in virus classification. Intervirology 31:241±254.

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

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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.

Wiens, J. J., and M. R. Servedio. 2000. Species delimitation in systematics: inferring diagnostic differences between species. Proc. R. Soc. London, Ser. B 267:631-636.

Species Concept: position

D.F.Silva