Principios de Taxonomia

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92j 4 What are Traits in Taxonomy? method in <strong>de</strong>fining what a species is: (1) Speciation does not always require a long period of time; (2) reproductive isolation can exist between populations having only small genetic differences; (3) genetic divergence does not necessarily lead to reproductive isolation between species; and (4) premating and postmating reproductive isolation have a markedly different genetic basis.
5 Diversity within the Species: Polymorphisms and the Polytypic Species 5.1 Preliminary Note Even today, it is still a common view that organisms that are clearly different with regard to traits are different species and that organisms that are less different with regard to traits are subspecies; this belief system does not withstand a persistent examination. Even on the DNA level, the extent of the differences and the certainty that they indicate the status of species cannot be equated. There are groups of individuals that differ genetically but belong to the same species, and there are groups of individuals that are similar in their DNA sequences but belong to different species. The first are evolutionarily old species, and the second are young species. Only a tiny fraction of the genome is involved with species differences (Orr, 1991). Species arise and are maintained by the action of very few genes, which have earned the moniker speciation genes. Speciation genes are genes for which the phenotypic traits cause reproductive isolation (see Section Speciation genes, pre- and postzygotic barriers in Chapter 6). Speciation genes are often responsible for the speciesspecific choice of food plants or for the occupation of a specific ecological niche. Speciation genes are also responsible for the choice of the correct species-specific sexual partner and hence are responsible for the perpetuation of species barriers. Speciation genes constitute only a small fraction of the genome (Orr, 2001). The vast majority of the genome is not involved in differentiating species and keeping them separate to prevent the merging of diverged populations (Chapter 4). One should not confuse the species-specific traits that cause reproductive isolation, and thus are responsible for maintaining species barriers, with those species-specific traits that became different by chance, that is, as a consequence of long-term separation leading to the cessation of sexual reproduction and gene exchange. The latter traits characterize the different species only arbitrarily, because they play no necessary role in blocking the gene flow. Evolutionarily young species differ in only a few traits, and these are mainly the traits for the maintenance of the species barriers (Schliewen et al., 2001). Evolutionary old species also differ in those traits that are not involved with keeping species separate from each other but which became different just by chance (Ferguson, 2002). Do Species Exist? Principles of Taxonomic Classification, First Edition. Werner Kunz. Ó 2012 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2012 by Wiley-VCH Verlag GmbH & Co. KGaA. j93
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Werner Kunz Do Species Exist?
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Werner Kunz Do Species Exist? Princ
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Contents Foreword XI Preface XV Col
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5.5 Are Carrion Crow and Hooded Cro
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7.8 Gene Trees are not Species Tree
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XIIj Foreword formed out in various
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Preface What is water? You would no
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Color Plates Do Species Exist? Prin
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Color PlatesjXIX
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230j Scientific Terms Autapomorphy
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232j Scientific Terms Gene-flow com
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234j Scientific Terms Monophylum A
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236j Scientific Terms barriers prev
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238j Scientific Terms Universal Uni
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2j Introduction would be sufficient
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4j Introduction A number of the col
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6j 1 Are Species Constructs of the
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2 Why is there a Species Problem? 2
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2.2 Can Species be Defined and Deli
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2.3 What Makes Biological Species s
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These conclusions indeed sound para
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2.4 Species: To Exist, or not to Ex
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If the species concept is, or even
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2.6 The Constant Change in Evolutio
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2.7 Can a Scientist Work with a Spe
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2.8 The Species as an Intuitive Con
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Contrary to this, it is always auto
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2.9 Taxonomy s Status as a Soft or
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2.11 Sociological Consequences of a
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Races are not populations of indivi
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2.12 Species Pluralism: How Many Sp
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2.12 Species Pluralism: How Many Sp
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2.13 It is One Thing to Identify a
Page 82 and 83: 2.14 The Dualism of the Species Con
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Page 86 and 87: 3 Is the Biological Species a Class
Page 88 and 89: 3.2 Class Formation and Relational
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Page 92 and 93: 3.4 The Difference Between a Group
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Page 96 and 97: 3.5 Artificial Classes and Natural
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Page 102 and 103: 3.9 The Linnaean System is Based on
Page 104 and 105: 3.10 Comparison of the System of Or
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142j 6 Biological Species as a Gene
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7 The Cohesion of Organisms Through
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7.2 The Problem of Displaying the P
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level of organisms with the next-hi
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Figure 7.4 Classification of organi
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7.4 How is a Cladistic Bifurcation
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7.5 Descent is not the Same Thing a
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Figure 7.7 Paraphyletic classificat
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7.6 Why are Paraphyla used Despite
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Figure 7.8 Phylogenetic trees at di
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Figure 7.10 Gene trees are not spec
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7.9 The Concepts of Monophyly and P
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7.10 Paraphyly and Anagenesis are M
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7.11 The Cladistic Bifurcation of a
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7.12 The Phylocode j213 Thus, if th
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7.12 The Phylocode j215 Figure 7.13
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8 Outlook What is a species? The an
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Index a aberration 96 Acinonyx juba
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essence 45, 46, 56, 58, 64, 65 esse
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Old World Ruddy Duck 150 Old World
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v vague boundaries 21, 184 vaguenes
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Principios de Taxonomia

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