Plant variation and evolution

Transcription

1 Plant variation and evolution D. BRIGGS S.M. WALTERS SECOND EDITION UNIVERSITATS- BIBLIOTHEK The right of the University of Cambridge all manner of books was granted by Henry VIII in The University has printed and published continuously since CAMBRIDGE UNIVERSITY PRESS Cambridge London New York New Rochelle Melbourne Sydney

2 Preface Acknowledgments Note on names of plants xi xiv xv 1 Looking at variation 1 'Kinds', species and natural classification 1 Individual variation 6 The nature of species 6 2 From Ray to Darwin 8 Ray and the definition of species 8 Linnaeus 10 Buffon and Lamarck 17 Darwin 20 Tests of specific difference 30 3 Early work on biometry 33 Commonest occurring variation in an array 35 Estimates of dispersion of the data 36 Histograms, frequency diagrams and the normal distribution curve 37 Other types of distribution 41 Comparison of different arrays of data 42 Complex distributions 44 Local races 46 Correlated variation 48 Problems of biometry 50 4 Early work on the basis of individual variation 52 Phenotype and genotype 53 Transplant experiments 55 The work of Mendel 58 Pangenesis 64

3 viii Contents Mendelian ratios in plants 65 Mendelism and continuous variation 68 Physical basis of Mendelian inheritance 74 5 Post-Darwinian ideas about evolution 80 Experimental investigation of evolution 80 The mutation theory of evolution 85 Neo-Darwinism 88 6 Modern views of the basis of variation 90 Chemical nature of the gene 90 Mutation and abnormalities 95 Molecular basis of mutation 98 Genetic and chromosomal differences between plants 99 Non-Mendelian inheritance 104 Phenotypic variation 105 Developmental variation 107 The control of phenotypic plasticity Breeding systems 115 Outbreeding 115 Inbreeding 122 Apomixis 125 Consequences of different reproductive modes 134 Breeding systems in wild populations Infraspecific variation and the ecotype concept 148 Turesson's pioneer studies and other experiments 148 Experiments by American botanists 158 The widespread occurrence of ecotypes 164 Clines 164 Factors influencing the variation pattern Species and speciation 172 The species concept 172 Gradual speciation 177 Abrupt speciation Gradual speciation and hybridisation 185 Evidence for gradual speciation 186 Natural hybridisation 191 The consequences of hybridisation: some theoretical considerations 196 Introgression and other patterns of hybridisation 201 Genetic investigations of hybridisation 208 Chemical studies of hybridisation 209 Interpretation of complex patterns of variation as cases of introgression 211

4 ix 11 Abrupt speciation 216 Polyploidy 216 Auto- and allopolyploidy ' 219 Experimental studies of polyploids 220 Reconstruction of the ancestry of polyploids 236 Properties of polyploids 242 The delimitation of taxonomic species in polyploid groups 244 Abrupt speciation at the diploid level Taxonomy and biosystematics 252 The success of biosystematics 252 The species concept 255 Biosystematics and phylogeny 258 Classification and phylogeny 259 The future of experimental studies Experimental methods in genecology 265 The term 'population' 266 Gamodemes in theory and practice 266 Experimental studies of gene flow 267 Sampling populations 274 Cultivation experiments 279 The designed experiment 283 The interpretation of experiments 289 Enzyme polymorphism Recent advances in genecology 294 The direction of genecological research 294 Examples of recent experiments 300 The speed of microevolutionary change 314 Results of disruptive selection in polymorphic populations 318 Patterns of variation in response to seasonal or irregular extreme habitat factors 319 Phenotypic plasticity 320 Population variation 321 The effects of chance in populations 329 Conclusions ' Evolution: some general considerations 332 The fossil record 333 Rates of evolution and the origin of angiosperms 334 Polyploid evolution and apomixis 340 The domestication of plants 347 Variety of patterns of evolution 350

5 16 Plant variation, nature conservation and the future 351 The nature conservation movement 351 What can the keen amateur contribute? 353 Prospects for the future 355 Further reading 356 Appendix 358 Glossary 361 References 366 Index 401