Bangor University DOCTOR of PHILOSOPHY Reciprocal
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Bangor University DOCTOR OF PHILOSOPHY Reciprocal transplantations to study local specialisation and the measurement of components of fitness. Mackenzie, Susan Award date: 1985 Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 05. Oct. 2021 RECIPROCAL TRANSPLANTATION TO STUDY LOCAL SPECIALISATION AND THE MEASUREMENT OF COMPONENTS OF FITNESS A thesis presented for the degree of Philosophiae Doctor of the University of Wales by Susan Mackenzie 1985 School of Plant Biology, University College of North Wales, Bangor, Gwynedd, United Kingdom. BEST COpy AVAILABLE TEXT IN ORIGINAL IS CLOSE TO THE EDGE OF THE PAGE CONTENTS AclmoPll ecig8IIIeD ts Chapter 1 General Introduction 1 Chapter 2 Reciprocal traosplant'expert.eDts 17 with 2 contrasting species Transplant experiments in Primula vulgaris 18 Transplant experiments in RsnUDculus repens 27 Discussion 38 Chapter 3 PhytOll8ter experiments 46 The influence of neighbours on the growth of 48 R. repens genets The influence of small-scale biotic and edaphic 52 variation on the growth of individual ramets Discussion 61 Chapter 4 Introduction to plant viruses 65 Chapter 5 The incidence and effect. of plant virusea 86 in natural populations Discussion 109 Chapter 6 The carryover of phenotypic differences 119 betweeD transplants Discussion 125 Chapter 7 General Discussion 131 Appendix I Appendix II References ACKNOWLEDGEMENTS I would like to thank my supervisor Professor J.t. Harper for his invaluable assistance throughout the duration of this study. I am also extremely grateful to Dr. J.I. Cooper for providing the stimulus and supervision of all the work on plant viruses. I thank Dr. Cooper, Dr. M.L. Bdwards, Dr. P. Massalski and the staff of the N.B.R.C. Institute of Virology in Oxford for their help with the virological techniques. Statistical advice was gratefully received from Chris Whitaker and John Connolly on numerous 'occasions and Steve Jones of the U.C.H.W. Computer Centre helped with some of the computing. In producing this thesis I am greatly indebted to Penny Anderson for allowing me to use her word processor and to Julia Watson for her help and co-operation whilst I was typing. Finally, the help and support my family and friends at all times is gratefully acknowledged. The study was supported by a grant fram the N.B.R.C. StMttARy Reciprocal transplant experiments have been made to investigate the .intra-specific variation in two clonal species, Primula vulgaris and RBDUDculus repens. Primula transplants performed best when returned to their native populations, indicating that they were differentia~ed in response to local conditions. There was marked variation in the degree of local specialisation of plants in different primrose populations and possible causes of this variation are discussed. Although buttercup transplants also showed great variability, there was no evidence that they were specialised, either between, or within, local populations. The lack of genetic specialisation in RBDUDculus repens may be due to its spreading growth form, widespread distribution and low level of seedling recruitment. In glasshouse experiments, the presence or absence of neighbours affected many parameters of buttercup growth. Within a genet the effect of edaphic and biotic heterogeneity was integrated, so that ramets in favourable conditions supported interconnected ramets in less favourable sites. Plants of R. repens vary phenotypically in different environments but appear to respond to heterogeneous local conditions by phenotypic plasticity of individual ramets rather than genetic specialisation. The assumption that differences between transplants are solely indicative of genetic specialisation has been questioned. Virus infection was detected in 7 of 14 primrose populations surveyed. Infected plants showed no symptoms of disease, yet they produced significantly fewer but larger leaves than uninfected plants. Differences between transplants which could easily be attributed to genetic variation may be due to differential virus infection. Furthermore, viruses may ultimately contribute to genetic differentiation and have a role as selective forces in the environment.. Phenotypic differences between ramets of the same genet of R. repens were maintained and even increased after 26 week's growth in a cammon environment. It is clearly imPortant in transplant experiments to use comparable phenotypes and virus-free plants when determining the role of genotype in the match between organism and environment. CHAPTER 1 General Introduction Introduction Over a' 1/4 of a million plant species have been distinguished by taxonomists attempting to order and classify the great variety of living plants. The taxonomists have defined these species on the basis of stable characteristics, mostly of floral morphology, and members of the same species are seen as differing "only in minor details" (Oxford English Dictionary, Concise Edition). Conspicuous morphological and physiological differences between the individuals within a species have frequently been ignored, as they concern taxono~ically "bad'"characters (see Snaydon, 1973) i.e. they show high genetic variability and are modified by environmental conditions. Yet, it is this variation which is important to the ecologist as it reflects the interaction between the plant and its environment. Characteristics such as: palatibility or toxicity; tall plants or short and different times of germination or flowering are crucial to plant performance. 'The study of intra-specific variation focusses attention on these ecologically-important differences whereas the taxonomic species may be too broad a category for the ecologist who is concerned with the actual variability expressed in the field. Darwin (1859) emphasised the importance of intra-specific variation in evolution: "No-one supposes that all the individuals of the same species are cast in the very same mould. These individual differences are highly important for us, as they afford materials for'natural selection to accumulate." Phenotypic differences between individual plants are indicative of the proximal effect of the environment on a plant's behaviour whereas, their genetic variability may reflect differential selection which has ultimately occurred in response to different habitat factors. This environmentally- induced genetic variation is frequently based on complex multiple gene 1 systems (Grant, 1971), unlike the big gene blocks on which the taxonomists' genetically stable characters are based, and alters in time and space with the heterogeneity of many environmental factors. Some genetic differences will also result from the chance fixation of different alleles (drift) and from pre-determined genetic characteristics (e.g. the founder effect). Consequently, it may be impossible to resolve intra-specific variants into discrete, stable units analogous to those of conventional taxonomy. However, by identifying the present pattern of intra-specific variation between and within natural populations and relating this to current environmental factors, we can gain a valuable insight into the forces of natural selection. The locally-differentiated population is a fundamental unit for evolutionary study because it represents the product of evolutionary processes at present operating on individual plants. It is only by the proximal observation of evolution in action that we can hope to understand the mechanisms of natural se1ection~ Intra-specific variation has been studied on a geographical scale, in plants growing in different populations in the same locality and even within populations. Morphological and physiological variants of the same species have been described and, more recently, differences in plant enzyme systems have been investigated. This variation has been correlated with various climatic, edaphic and biotic aspects of the environment. A number of these studies are reviewed below. 2 Experimental Studies of Intra-specific Variation in Plants I.Transplant Studies Morphological Modifications Early investigations of intra-specific variation considered the morphological diversity of plants growing in different climatic conditions. Plants were cultivated from seed and grown in experimental gardens at contrasting altitudes: 180m; 56S. and 2l95m (Kerner, 1895). Individuals of the same species varied in morphological characteristics when grown in the different sites. These intra-specific differences were not transmitted to the progeny but represented temporary (phenotypic) modifications in response to environmental forces. The effects of contrasting environments were compared within a single genet by transplanting c~ones, or ramets, of the same plant into different altitudinal locations (Bonnier, 1890). A number of modifications were noted·,