Principios de Taxonomia

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126j 5 Diversity within the Species: Polymorphisms and the Polytypic Species females locate suitable nests by observing the host bird preparing its nest and beginning incubation, waiting for hours in a concealed place if necessary. Moreover, it is probable that the host birds are identified acoustically by their song. The ability to locate a proper nest must also be determined to a large extent hereditarily given that no parental instruction is possible and that the only available memories are from their own hatching and raising. Furthermore, brood parasitism can only be successful when the cuckoo s eggs mimic the eggs of the host birds with respect to size, color and pattern. In the Eurasian Cuckoo Cuculus canorus, there are more than a hundred genetic variations that determine the eggs sizes and colorations. The individual female, including its female descendants, only lays eggs of one particular type. This egg mimicry can only be explained by the presence of polymorphic alleles. With respect to understanding the species concept, the primary challenge is not simply explaining perfect adaptation but how this adaptation can be explained by a number of linked genes, all of which must work together as a linkage group in a cuckoo female. The time of egg deposition, the identification of the host and the coloration of the eggs are supported by genetic dispositions that must not be separated by genetic crossing-over events. This is because a particular cuckoo female cannot have half of its traits adapted to one host bird and the other half to another host bird. None of the adaptation traits that are attuned to a particular host bird can recombine. The sum of these traits must be inseparably and genetically linked to each other. Accordingly, there are genetically distinguishable Robin cuckoos, Black Redstart cuckoos, Thrush cuckoos, Reed Warbler cuckoos, and so on. Why, then, are not there 200–300 species of cuckoos in Eurasia? The answer to this question is as follows. The adaptation to a particular species of host bird is only maintained by the female cuckoos. In males, there is no host specificity. Accordingly, just as with the mimicry polymorphism of female Swallowtail butterflies (see above), the cuckoo morphs are sex-related. Why is it the female sex that exhibits polymorphism? It does not appear to be a coincidence that both butterfly and bird morphs are determined exclusively by the female sex. This is because in birds, just as in butterflies, females, as an exception, are the heterogametic sex. In butterflies and birds, the females are of the XYconstitution (occasionally referred to as ZW), whereas the males are of the homogametic XX constitution. The Y (or W) chromosome contains a large percentage of genes that are embedded in heterochromatin and thus are protected from recombination. These protected genes are referred to, in this instance, as a linkage group. It is a safe assumption that all of the genes that determine the distinct phenotype of a particular morph are located on the Y chromosome, the genes of which are generally protected from genetic crossing-over. This situation would explain (1) how an entire battery of genes is linked and inherited as a whole and (2) why these genes are inherited along the maternal line. If the cuckoo was homogametic in the female sex, as in mammals, brood parasitism likely could not exist.
6 Biological Species as a Gene-Flow Community 6.1 The Definition of the Gene-Flow Community The species concept of the gene-flow community has been established at the beginning of the twentieth century by the British scientist Edward Bagnall Poulton (Poulton, 1903; Poulton, 1938). It was then in 1937 substantially upgraded by Theodosius Dobzhansky, a geneticist who was born in the former Soviet Union, by combining taxonomy with genetics (Dobzhansky: Genetics and the origin of species 1937). In 1942 the concept received a successful advocate in Ernst Mayr who propagated this species concept for a broad audience (Mayr: Systematics and the origin of species 1942). Finally, Michael Ghiselin then substantiated this species concept philosophically in 1997 (Ghiselin: Metaphysics and the origin of species 1997). Despite its many fathers, the concept of the gene-flow community is today most of all associated with the name Ernst Mayr; for it was him who popularized this concept and referred to it as the actual biological species concept, so that Mayr is displayed in many textbooks as the originator of this species concept. A gene-flow community is a community of organisms that are connected by gene flow through sexual reproduction. Sexual gene flow is also called lateral gene flow and is opposed to vertical gene flow, which is the transfer of genes from parental organism to its filial generations. Interorganismic connection by lateral gene flow is a distinctive feature only for those organisms that have a biparental reproduction, (organisms that can only reproduce if there are two parents). Plants and animals that undergo only uniparental reproduction are clearly distinguished from biparental organisms because they are not connected by lateral gene flow. Those organisms that reproduce only vegetatively or parthenogenetically have no sexual gene transfer and therefore cannot be considered to form gene-flow communities. As the species concept of a gene-flow community cannot be applied to uniparental organisms, all of those organisms are, in the sense of a gene-flow community, species-less (Ghiselin, 1997). If the species definition of lateral gene flow were applied to 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. j127
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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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Color PlatesjXXI
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Color PlatesjXXIII
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Color PlatesjXXV
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Color PlatesjXXVII
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Color PlatesjXXIX
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Color PlatesjXXXI
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Color PlatesjXXXIII
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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
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2.14 The Dualism of the Species Con
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2.14 The Dualism of the Species Con
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3 Is the Biological Species a Class
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3.2 Class Formation and Relational
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3.3 Is the Biological Species a Uni
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3.4 The Difference Between a Group
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3.4 The Difference Between a Group
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3.5 Artificial Classes and Natural
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3.6 The Biological Species Cannot b
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3.7 The Biological Species as a Hom
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3.9 The Linnaean System is Based on
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3.10 Comparison of the System of Or
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3.11 The Relational Properties of t
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68j 4 What are Traits in Taxonomy?
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176j 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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