viernes, 25 de junio de 2010

Pluralism of concepts: the BSC

D.F. Silva

The idea that there is no single, right species definition, is known as pluralism, this being one response to the multiple species definitions (Maclaurin & Sterelny.2008). This pluralism is reflected in the diversity of species concepts. (Wilkins 2002) has listed 26 distinct species concepts along with synonyms. Here, I include one concepts broadly used and debated, in order to consider how to recognize species.

The BSC (biological species concept), is considered as an interbreeding concept or reproductive isolation concept (Lee 2003; Wilkins 2009 ) . The basis for this consideration lie in the concept´s specifications: Species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups (Mayr 1942),

So the reproductive isolation in nature, was the key factor in identifying and maintaining species as discrete entities (Claridge 2009). But this key factor, was the principal trouble at the time to recognize the species. Thus, in practice the BSC would recognize that different species are characterized by distinct barriers, isolating mechanism or by the SMRS (the Specific Mate Recognition System of Paterson). However the species taxa are only rarely recognized by direct studies of the SMRS (Claridge 2009). Further, neither asexual nor Parthenogenetic organism can be considered under the BSC because they don’t have a functional system of mate that leads to the fusion of gametes and the reproductive isolation. The geographical variation of the populations vary from almost nothing to large differences but the reproductive isolation in the field can be determined only for sympatric populations , then the allopatric forms began to be recognized with a pragmatic approach as subspecies (Mallet 2005).

Perhaps one of the principal problems with the BSC is the practical impossibility of establish the reproductive isolation between natural populations (Balakrishnan 2005). Another point of criticism, including lack of temporal dimensión, the BSC defines the species only in some point in time (Lee 2003; Balakrishnan 2005). Under the BSC, as the other concepts related to the interbreeding concepts, the species at a given point in time are groups of organisms which interbreed with each other and are reproductively isolated from other species. Likely employing gene flow would tend to delimit the same taxa as species, and thus to depict the boundary of the species rank in the same place (Lee 2003).

Claridge, M. 2009. Species Are Real Biological Entities. In: Contemporary debates in Philosophy of Biology. (Ed. F. Ayala and R. Arp). Wiley-Blackwell. p 91-109

Lee, M. S. 2003 Species concepts and species reality: salvaging a Linnaean rank. J. Evol. Biol. 16. Blackwell Publishing ltda.

Maclaurin, J. & Sterelny, K. 2008. What is biodiversity?. The University of Chicago Press, Ltd., London. p 31.

Mallet, J. 2005. Species Concept. p367-373.

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

Wilkins, J. 2002. Summary of 26 species concepts. Copyright © 2002 John S. Wilkins

Wilkins, J. 2009. Species: A History of the Idea. University of California Press, Ltd. London.p 197- 201.

jueves, 24 de junio de 2010

Biological Species Concept

Jimenez Silva, C. L.

Universidad Industrial de Santander
The biological species concept defeat the "typological thinking", Mayr's foundations to refute it was the population biology vision, with which reverses the meaning of species as type and replaced with a statistical group approach. the Population biologist emphasizes the uniqueness of each thing in the organic world. Individuals, or any kind of organic entity, build populations from which we can determine the arithmetic mean and the statistical variation. Averages are merely statistical abstractions, only individuals have actually made up of those populations. For the typology, the type (eidos) is real and the variation an illusion, while for the population biologist the type (average) is an abstraction and only the variation is real. (MAYR, E. 1959)

A population forms a "specie" only with respect to other populations. Belonging to a different specie is not about differences, it is about distinguish and relate. The Biological interpretation introduce to the multidimensional concept of species, which means that it should be considered as a group of stocks that actually or potentially interbreed. Such species, to preserve their identity, can't coexist in the same place at the same time, applying the concept to allopatric species is determined on the possibility of mutual intersection. As the concept of "species" as Mayr that applies to biological individual, acquires a double meaning: on the one hand it refers to the dimensionless-that Mayr interpreted as the reproductive continuum, and secondly, concerns to the multidimensional condition, whereby the possibility of gene flow can be almost unlimited. It also includes raising Population meaning: "The species are natural population groups really or potentially interbreeding , reproductively isolated from other similar groups" MAYR, E. (1942). Comparable to those proposed by Dobzhansky, 1941, stating: "A species is a reproductive community wider ... of sexual individuals and that fertilize each other, they share a common gene pool".

One of the problems of the species is limited to the consequences of consider it was the result of a "category of thought" taking it to an artificial incompatible condition with the biological reality. Mayr criticizes the taxonomists, who believe that this concept treats individuals as an aggregate of inanimate objects, taking it as inappropriate for the dynamic behavior of a population change. Affirming that "The species is therefore a dynamic concept, population, inextricably tied to genetic recombination events, whose meaning makes possible the emergence or splitting of one species into another" (MAYR, E 1968). Defending and a realistic notion of species derived from their interactions with the environment and other species. MAYR, E. (1949) In the biological species concept, although two species are morphologically indistinguishable, each one has a genetic system, behavioral and ecological separate, isolated by a real biological discontinuity in a meaningful context specific population based on genetic transformation.

DOBZHANSKY, T.-: (1941) Genetics and the Origins of Species. Columbia, Biological Series, N.XI, 2a

MAYR, E.: (1959) Species concepts and definitions. En E. MAYR, E.: The species problem (Amer. Assoc. Adv. Sci. Publ. No. 50), 1-22.

MAYR, E.: Animal Species and Evolution., Ariel, 1968. p. 32

MAYR, E.: (1942 ) T(Systematics and the Origin of Species. Columbia University Press. New York.

MAYR, E.: (1949) Speciation and selection. Proc. Amer. Phil. Soc. 93:514-519.

miércoles, 23 de junio de 2010

Biological Species Concept and Species Boundaries

Gualdrón-Diaz Juliette

Almost all studies in biology, whether at the level of molecules, cells, individuals or populations, are typically referenced to the level of the species. In the field of conservation biology, assessments of biodiversity are made at the level of the species: typical criteria include species richness, numbers of endemic species and the number or presence of endangered species in given areas (Myers et al. 2000). The accurate identification of species is crucial both to research in all areas of biology and to biodiversity conservation. Classical taxonomists classified individuals as members of a species based on a suite of shared morphological characters that were diagnostic and differentiated them from other such morphologically defined groups. In recent times, behavioural and ecological characters have also been increasingly used (Balakrishnan 2005).

One of the species concepts has been almost universally adopted by students of behavior, by most ecologist and those animal taxonomists, as well as by the molecular biologists (Avise and Ball 1990) is the Biological Species Concept (BSC). The BSC is most closely associated with Ernst Mayr (1942), who defines species based on their ability to interbreed: species are considered as “natural” entities distinguishable from other species by the criterion of reproductive isolation and not overall phenotypic similarity. The BSC has been criticised for several reasons: its inapplicability to asexual taxa (Mishler and Theriot 2000; Wheeler and Platnick 2000), lack of a temporal dimension (Willmann and Meier 2000), logical fallacy and the difficulty of applying it to allopatric populations (Mallet 1995).

One of the major problems, not only in BSC, but in any species concept is criterion for differentiating and delimiting species. If one accepts reproductive isolation as a sufficient criterion for delimiting species, then how recognize and delimit species using reproductive isolation?, a solution to this problem is delineate species boundaries using morphology, for this is necessary to examine the concordance between morphological and “biological” species boundaries (Balakrishnan 2005). Nevertheless, in certain groups is relatively easy such as crickets because the calling songs of cricket species are often reliable indicators of reproductively isolated populations (Shaw, 1999). Therefore the concordance in such behavioural and morphological characters would imply that phenetic clusters based on morphology correctly reflect the species boundaries defined by reproductive isolation. But for taxa that do not possess such behavioural associated with morphological is difficult to define species by BSC. In practice, even strong adherents of the BSC use phenetic similarities and discontinuities for delimiting species. If the organisms are phenotypically similar, they are considered conspecific until a reproductive barrier is demonstrated. However a practical difficulty encountered is that some populations may acquire reproductive isolation but minimal morphological difference, whereas other populations may acquire conspicuously different morphologies but no isolating mechanisms (Mayr 2000). Reproductive isolation may thus be looked upon as a sufficient but not necessary condition for delimiting species boundaries.

Although the BSC is the species concept most widely adopted, and is potentially useful in the analysis of speciation from the perspective of population genetics (Templeton 1989), it has some serious difficulties that make it inadequate, besides question unresolvable using the biological definition. As a result, most taxonomists, even those that accept the biological species concept, continue to use morphology and other phenotypic characters in order to delineate species boundaries.


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A perspective from the Biological Species Concept

Susana Ortíz B.

The hight biodiversity and complexity of the biological systems, is one of the greatest challenges at the time to recognize and delimit species as real entities in nature (Shcherbakov, 2010; Purvis and Hector, 2000; Sites and Crandall, 1997). Efforts to describe and identify these entities have resulted in the formulation of multiples species concepts contrasting with differents philosophical and epistemological approaches. Perhaps, the most widely discussed concept is the Biological Species (BSC). This concept stipulates the specie as a group of interbreeding natural populations that are reproductively isolated from other such groups and share a common place (Mayr 1942-1996). Although, the concept has been widely adopted in various areas is controversial and unyokeable under certain context. Criticism have been focused against some aspects including its lack of universality (Balakrishnan, 2005). This limitation is manifest by its inapplicability to sexual taxa (Wheeler and Platnick, 2000), and fossils; the latter, given the impossibility of identify its reproductive potential.

The capacity of interbreeding is the main criterion to define species in the BSC, which in theory implies that species no interbreed with members of other species, and they are reproductively isolated (Ayala, 2010). However, this does not mean only geographical isolation, structural and behavioral barriers could be considered prevent interbreeding. Based on the above, the concept is not clear in defining the causal order between interbreeding and reproductive isolation. This is consistent with the formation of hybrids and also the practical difficulty of determining a specie in allopatric populations, ignoring the potential to interbreed with other species under contingent conditions and the ability to produce real fertile offspring (Mallet, 1995). So, because mechanisms of reproductive isolation differ among taxa, the BSC cannot be absolute in the determination of species (Claridge, 1997).

An important aspect addressed in all conceptualizations of species is related to the definition of its status as a class or as individual. According to Goldstein & DeSalle (2000)the BSC defines the species as a class, which provides an ambiguous criterion to group organisms and result in the BSC might not be monophyletic (Donoghue, 1985). However, according to Dobzhansky (1950), the biological specie is the largest and most inclusive mendelian population then recognizes the evolution and thus the species as fundamental units of evolution, while higher taxonomic categories such as gender, cataloging families and orders are artificial, made for convenience and do not necessarily reflect evolutionary relationships (Jody, 2001). Moreover, the BSC concept is conceived in a population notion, where "populations" are seen as reproductive units which share a common gene pool in a context of reproductive isolation. Although the concept frames the unique properties of biological systems such as reproduction and crossover potential, other properties are not directly unlink, for example, recognition of conspecifics and gene flow (Mallet, 1995).

Additionally, the concept dispose that the taxonomy of natural species should be the conceptual schema of genetic populations, because a community of organisms that cross, is a gene pool which gives an identity that makes relatively recognizable species (Dobzhansky, 1937), but this appears not be the case in cryptic species. In despite of the mechanisms that can give rise to real species in nature and that are not recognized by the BSC, it have a strong theoretical component, which as Mayr (1996) said not only refers to the description and recognition of the species in nature, but the causes and processes associated with them.

Finally, the species concept can be extended to virology, but maybe the BSC is not the most adecuate; In the first place, viruses are genetic and evolutionary entities but is impetuous to affirm that are biological entities. Nonetheless, some features of BSC are applicable, for example, the specie is the evolutionary face, also as the BSC the members of a species resemble one another, and differ from other species. The difference between BSC and specie in viruses lies in some processes and mechanisms responsible of this identity. Obviously, viruses do not interbreed, but the recombination could be considered loosely as a mechanism that similarly allows genetic exchange, although this event is quite rare in viruses (Lai, 1992). To conclude, clearly these are just some aspects and implications of the BSC in virology, but probably there are many issues to be adressed in this and others areas, for now, even though the BSC is an important conceptual and operational base, it cannot offer universal yardstick to delimit species in nature.


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