martes, 28 de octubre de 2008

BCS, conservation biology and biodiversity.

Always a biologist is faced with the problem of identification of species of a particular group of organisms, the first tool to determinate is the morphology as decisive criterion of species, however, the existence of sibling species, different morphological types or individual genetic variations as a consequence of the mosaic evolution, becomes this approach arbitrary at the time of determinate species. Thus, the concept of biological species (BCS) arose, as a result of the unsatisfactory inference of morphological species concept, since the BCS takes other factors such as their genetic identity.

Mayr's BCS is from my point described as an evolutionary strategy to keep the genetic identity certain populations, or as he says: "keep the gene pool well-balanced and well-adapted genotypes or harmonics," (Mayr, 1996), whose mechanism of protection against any kind of destabilization by recombination, diminishes the frequency of the exchange of genes between the groups, is interbreeding isolation. Likewise, the definition and the operation of BCS consistent with one another. However, the main problem is its application, because if we follow the BCS cannot go beyond the organisms with sexual reproduction, so those asexual organisms would be excluded, that would become impractical for studies of conservation and biodiversity, since the latter seeking a universal definition and objective, thus, as a consensus of species richness and biodiversity hotspots (Agapow, 2004).

Otherwise, the geography is an unsolved problem for the BCS, as far as allopatric populations are concerned (in addition to any already existing applicability problems), according to Mayr these populations are those that have not reaching or ever reach the status of species, characterized by a certain kind of continuous isolation. However, Zink in 2004 from a study using mitochondrial DNA, argue against considering subspecies as proxies for units of conservation because he demonstrates that certain avian subspecies do not have a clear population genetic structure, and that it is inconsistently related to subspecies boundaries sensu Mayr.

Hence, as far as I’m concerned the BCS is a vicious circle around the sexual organisms (is logical that the genetic barrier to sexual organisms, is the interbreeding isolation), which more than a practical concept of demarcation is an evolutionary strategy of sexual stabilization gene, that becomes in the game of apply and not apply, turning both ambiguous and expensive for two primary approaches where the concept of species is critical and decisive, biodiversity and conservation.


Agapow, PM. Bininda, OR. Crandall, KA. Gittleman, JL. Mace, GM. Marshall, JC. & Purvis, A. 2004. The impact of species concept on biodiversity studies. Q Rev Biol. 79:161-79.

Mayr, E. 1996. What is a species and what is not?. Philosphy of Science. 63: 262–277.

Zink, R. 2004. The role of subspecies in obscuring avian biological diversity and misleading conservation policy. Proc. R. Soc. Lond. B 271, 561–564

lunes, 27 de octubre de 2008

Biological Species Concept

Morales-Guerrero, A. M.
Universidad Industrial de Santander
“The BSC can illuminate
only a small fragment
of the Tree of Life” (Agapow et al. 2004).
There are two different questions involved to the Species Concept:
I. The question concerning the reality of phenomena or of objects in nature we want to name with the term “species” (this is the theoretical problem).
II. The criteria for the identification of species (and this is practical problem) (Wolfgang, 2005).

The solution of the practical problem depends on the definition of the term “species” we want to use (Wolfgang, 2005); currently the issue of species “reality” is central to decision of how to approach species delimitation and to understand the ontology of species (Goldstein & DeSalle, 2000). I share the view that species are spatio-temporally bounded entities (rather than classes defined by some common property), that species per se are not involved in processes - they are effects, not effectors (Kluge, 1990).

A short definition of the BSC is: ‘‘Species are groups of interbreeding natural populations that are reproductively isolated from other such groups’’ (Mayr, 1996). In this definition of the BSC, the species are considered as “kinds” (i.e. categories or classes) distinguishable from other species by the criterion of reproductive isolation and not overall phenotypic similarity.

The biological species concept is important because it places the taxonomy of natural species within the conceptual scheme of population genetics but has been criticized for several reasons; including the lack of a temporal dimension (Balakrishnan, 2005), for this reason is not possible to talk about age of the species or origin of the species, as a consequence the BSC definition may be only for populations that coexist in time-space and which live in sympatry. In this way the BSC also denies any idea about the fossil species due to the inability to measure its reproductive potential (Fernández et al. 1995), others problems are the practical impossibility of ascertaining reproductive isolation between populations in the wild and the inapplicability concept for asexual organisms (Balakrishnan, 2005), so this definition leaves a vast number of organisms with a nebulous status (Agapow et al. 2004). Finally there are also problems in the structure of the concept, because the BSC confuses the pattern with the process or the isolation with the speciation (Fernández et al. 1995).

The criteria for the identification of species or Operational methods (concerned with how a species may be delimited rather than what it represents) are a necessity (Sites & Crandall, 1997). Today, the empirical issue of the species delimitation is receiving increased attention and several methods have been proposed for delimiting species in a statistically rigorous framework.

According to Site & Marshall (2004), the methods for species delimitation are divided into two:
“Nontree-based methods delimit on the basis of gene flow assessments, whereas tree-based methods delimit species as historical lineages”

Templeton (2001) recently advocated application of his NCA method (Templeton et al. 1995) to the problem of species delimitation; this method is based in the reconstruction of tree and reproductive isolation and was designed for the concept of cohesive species. NCA takes into account all of the available information on the geographic and phylogenetic position of haplotypes and statistically tests for their association, and it can be applied to many different levels within a clade to determine whether a speciation event can be inferred with significant statistical support given the data available (Templeton, 2001). Though this was developed for tests cohesive species, is applicable to delimit species according to BSC, because this indirectly estimating gene flow within and between hypothesized species, so the reproductive isolation may thus be looked upon as a informative but not necessary condition for delimiting species boundaries, where it does exist, it is likely to unambiguously delimit species.
-Agapow, PM. Bininda, OR. Crandall, KA. Gittleman, JL. Mace, GM. Marshall, JC. & Purvis, A. 2004. The impact of species concept on biodiversity studies. Q Rev Biol. 79(2):161-79.
-Balakrishnan, R.2005. Species concepts, species boundaries and species identification: A view from the tropics. Systematic biology. 54: 689-693.
-Fernandez, F., Hoyos, J.M. & D.R. Miranda. 1995. Especie: Es o Son? Número especial Evolución. Innovación y Ciencia. Colombia. 4(1):32-37.
-Goldstein, P. & DeSalle, R. 2000. Phylogenetic species nested hierarchies and character fixation. Cladistic. 16: 364-384.
-Kluge, AG. 1990. "Species as historical individuals." Biology and Philosophy. 5 (4): 417-431.
-Mayr, E. (1996): What is a species and what is not?. Philosphy of Science. 63: 262–277.
-Sites, JW. Jr, & K. A. Crandall. 1997. Testing species boundaries in biodiversity studies. Cons. Biol. 11:1289–1297.
-Sites JW Jr, Marshall, JC. 2004. Operational criteria for Delimiting Species. Annu. Rev. Ecol. Evol. Syst. 35:199–227.
-Templeton, AR. 2001. Using phylogeographic analyses of gene trees to test species status and boundaries. Mol. Ecol. 10:779–91.
-Templeton, AR. Routman, E. & CA. Phillips 1995. Separating Population Structure from Population History: A Cladistic Analysis of the Geographical Distribution of Mitochondrial DNA Haplotypes in the Tiger Salamander, Ambystoma tigrinurn. Genetics. 140: 767-782.
-Wolfgang Wagele, J. 2005 Foundations of Phylogenetic Systematics. verlag Dr. friedrich pfeil. Munchen.