Principios de Taxonomia

Recommendations

Info

150j 6 Biological Species as a Gene-Flow Community incompatibility is not a straightforward consequence of evolutionary divergence, which is the spatial and temporal distance of the populations from each other. No biological law necessitates that phylogenetically distant populations must automatically be reproductively incompatible. The organisms in evolutionary distant strains become reproductively incompatible only by chance, not by any biological law, as the largest proportion of the genes has nothing to do with species barriers. It would be too easy to interpret the situation such that, in the case of reproductive incompatibility, the two populations just had diverged far enough from each other that they were no longer genetically compatible. Genetic incompatibility is not a necessary consequence of the divergence between two populations. Instead, reproductive incompatibility is the result of the mutual incompatibility of the alleles of a few particular genes, the interactions of which lead to restrictions on vitality or fertility. Such genes are called speciation genes. Speciation genes are responsible for speciation. They are responsible for keeping two species segregated from each other. These genes cause the splitting of species. They include, for example, the genes that control the mating choice. Their task is to prevent mating with different species. Speciation genes also control adaptation to species-specific food plants, habitats or climates. It is an important task of modern taxonomy to find genes of this kind (Wu, Johnson, and Palopoli, 1998). The statement that speciation is primarily founded on very few particular genes, not on overall genetic divergence, is substantiated by the example of the New World Ruddy Duck (Oxyura jamaicensis) and the Old World Ruddy Duck (Oxyura leucocephala) (see below). The species were separated from each other for a long time. They are phylogenetically distant and became phenotypically very different; however, after the New World Ruddy Duck was introduced to Europe, it began to hybridize with the endemic European Old World Ruddy Duck. Presently, the latter is seriously endangered as a separate species because there appears to be no hybridization barrier. Despite a long period of separation, no genetic incompatibility has evolved between these two species. If the further expansion of the New World Ruddy Duck cannot be stopped, the Old World Ruddy Duck may become extinct by hybridization in the next few decades. Speciation genes must be separated into prezygotic and postzygotic speciation genes. Prezygotic speciation genes are those that control the processes that are responsible for the final goal of sperm-egg fusion and, therefore, zygote formation between two organisms. For this reason, they are called prezygotic genes. In the case of external fertilization, prezygotic speciation genes code for signaling molecules that allow sperm cells to fuse with the eggs of the correct species or that prevent sperm cells from fusing with the eggs of the wrong species. Furthermore, they code for receptor molecules on the egg s surface that control the fusion of sperm cells with egg cells of the correct species. These receptor molecules could also inhibit zygote formation between different species. In the case of internal fertilization, prezygotic speciation genes control copulation. If two organisms belong to different species, the prezygotic speciation genes prevent a successful copulation. Therefore, in the case of internal fertilization, the term
prezygotic barrier is almost synonymous with the term premating barrier. For example, prezygotic speciation genes regulate species-specific plumage and song traits in birds, which serve partner identification and stimulate the willingness of the female to mate. Prezygotic speciation genes cause assortative mating; assortative mating refers to the selective choice of a sexual partner of the correct species and a sexual aversion towards the members of a different species. Prezygotic barriers also include structural traits of the copulation apparatus; for example, in the case of many insects, there are purely mechanical reasons to not be able to copulate with a foreign species. In many cases, prezygotic barriers are a complex combination of several distinguished behavior patterns that interact between the mating partners. That is the reason why prezygotic barriers often cannot be reproduced under experimental conditions with animals in captivity. In addition to prezygotic barriers, there exist postzygotic barriers that also prevent crossing among the members of different species. Similar to the prezygotic barriers, the postzygotic barriers are regulated by specific genes, called postzygotic speciation genes. Postzygotic barriers are those that become noticeable only after hybrid formation has already occurred. In other words, postzygotic barriers can only be effective if prezygotic barriers do not exist or if the prezygotic barriers were imperfect ( leaky ). Postzygotic speciation genes are responsible for any type of hybrid dysgenesis, which means properties of the F1 offspring that disadvantage a hybrid, compared to purebred offspring. In many cases, species hybrids are not able to effectively compete with purebred offspring with respect to their vitality and/or fertility. In extreme cases, a reduction in vitality appears already in early embryonic development; the coordinated development of specific cells or tissues is deranged. In other cases, however, postzygotic barriers become noticeable only after several generations because the reduction in the vitality or fertility is faint and is not easy to observe. The result only has an impact from competition with purebred rivals. That is the reason why postzygotic barriers often cannot be reproduced under experimental conditions with animals in captivity. 6.15 Hybrid Incompatibility 6.15 Hybrid Incompatibilityj151 Hybrid incompatibility is one of the possible reasons why two organisms belong to different species. However, it has to be considered that that are many examples that isolation by distance also includes hybrid incompatibility. Alternatively, it has to be considered that that are many examples of allopatrically separated organisms that are not incompatible. Hence, hybrid incompatibility is not the same as speciation. Until today, little has been known about genes that lead to allelic incompatibility in a species hybrid and, thus, about postzygotic disturbances. Little is known with respect to how many genes are involved and what, in each case, leads to the discrepancies. It is not very scientific to say that phylogenetically distant organisms have simply drifted far apart from each other genetically and that the drift causes the hybrids to be reduced in vitality and fertility. Instead, it should be one of the first tasks
Page 2 and 3:
Werner Kunz Do Species Exist?
Page 4 and 5:
Werner Kunz Do Species Exist? Princ
Page 6 and 7:
Contents Foreword XI Preface XV Col
Page 8 and 9:
5.5 Are Carrion Crow and Hooded Cro
Page 10 and 11:
7.8 Gene Trees are not Species Tree
Page 12 and 13:
XIIj Foreword formed out in various
Page 14 and 15:
Preface What is water? You would no
Page 16 and 17:
Color Plates Do Species Exist? Prin
Page 18 and 19:
Color PlatesjXIX
Page 20 and 21:
Color PlatesjXXI
Page 22 and 23:
Color PlatesjXXIII
Page 24 and 25:
Color PlatesjXXV
Page 26 and 27:
Color PlatesjXXVII
Page 28 and 29:
Color PlatesjXXIX
Page 30 and 31:
Color PlatesjXXXI
Page 32 and 33:
Color PlatesjXXXIII
Page 34 and 35:
230j Scientific Terms Autapomorphy
Page 36 and 37:
232j Scientific Terms Gene-flow com
Page 38 and 39:
234j Scientific Terms Monophylum A
Page 40 and 41:
236j Scientific Terms barriers prev
Page 42 and 43:
238j Scientific Terms Universal Uni
Page 44 and 45:
2j Introduction would be sufficient
Page 46 and 47:
4j Introduction A number of the col
Page 48 and 49:
6j 1 Are Species Constructs of the
Page 50 and 51:
2 Why is there a Species Problem? 2
Page 52 and 53:
2.2 Can Species be Defined and Deli
Page 54 and 55:
2.3 What Makes Biological Species s
Page 56 and 57:
These conclusions indeed sound para
Page 58 and 59:
2.4 Species: To Exist, or not to Ex
Page 60 and 61:
If the species concept is, or even
Page 62 and 63:
2.6 The Constant Change in Evolutio
Page 64 and 65:
2.7 Can a Scientist Work with a Spe
Page 66 and 67:
2.8 The Species as an Intuitive Con
Page 68 and 69:
Contrary to this, it is always auto
Page 70 and 71:
2.9 Taxonomy s Status as a Soft or
Page 72 and 73:
2.11 Sociological Consequences of a
Page 74 and 75:
Races are not populations of indivi
Page 76 and 77:
2.12 Species Pluralism: How Many Sp
Page 78 and 79:
2.12 Species Pluralism: How Many Sp
Page 80 and 81:
2.13 It is One Thing to Identify a
Page 82 and 83:
2.14 The Dualism of the Species Con
Page 84 and 85:
2.14 The Dualism of the Species Con
Page 86 and 87:
3 Is the Biological Species a Class
Page 88 and 89:
3.2 Class Formation and Relational
Page 90 and 91:
3.3 Is the Biological Species a Uni
Page 92 and 93:
3.4 The Difference Between a Group
Page 94 and 95:
3.4 The Difference Between a Group
Page 96 and 97:
3.5 Artificial Classes and Natural
Page 98 and 99:
3.6 The Biological Species Cannot b
Page 100 and 101:
3.7 The Biological Species as a Hom
Page 102 and 103:
3.9 The Linnaean System is Based on
Page 104 and 105:
3.10 Comparison of the System of Or
Page 106 and 107:
3.11 The Relational Properties of t
Page 108 and 109:
68j 4 What are Traits in Taxonomy?
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
94j 5 Diversity within the Species:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141: 100j 5 Diversity within the Species
Page 168 and 169: 128j 6 Biological Species as a Gene
Page 226 and 227: 7 The Cohesion of Organisms Through
Page 228 and 229: 7.2 The Problem of Displaying the P
Page 230 and 231: level of organisms with the next-hi
Page 232 and 233: Figure 7.4 Classification of organi
Page 234 and 235: 7.4 How is a Cladistic Bifurcation
Page 236 and 237: 7.5 Descent is not the Same Thing a
Page 238 and 239: Figure 7.7 Paraphyletic classificat
Page 240 and 241:
7.6 Why are Paraphyla used Despite
Page 242 and 243:
Figure 7.8 Phylogenetic trees at di
Page 244 and 245:
Figure 7.10 Gene trees are not spec
Page 246 and 247:
7.9 The Concepts of Monophyly and P
Page 248 and 249:
7.10 Paraphyly and Anagenesis are M
Page 250 and 251:
7.11 The Cladistic Bifurcation of a
Page 252 and 253:
7.12 The Phylocode j213 Thus, if th
Page 254 and 255:
7.12 The Phylocode j215 Figure 7.13
Page 256 and 257:
8 Outlook What is a species? The an
Page 258 and 259:
Index a aberration 96 Acinonyx juba
Page 260 and 261:
essence 45, 46, 56, 58, 64, 65 esse
Page 262 and 263:
Old World Ruddy Duck 150 Old World
Page 264:
v vague boundaries 21, 184 vaguenes
show all

Principios de Taxonomia

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?