The Leaf Economics Spectrum (LES) describes the continuous range of leaf ecophysiological strategies that plants across the globe utilize to achieve a net-positive return on their resource investment. This spectrum is measured by traits such as leaf mass per area, leaf nitrogen, and leaf lifespan. Unsuitable leaf trait combinations are selected against in nature due to a net-loss on the return of initial resource investment, while some potentially extremely effective trait combinations may not be possible due to genetic constraints. Existing genetic variation in LES traits, however, suggests the spectrum may be less rigid than previously expected. To test this, we exploit phenotypic plasticity by subjecting cultivated sunflower, Helianthus annuus, to environmental stress to generate variability in LES traits. In a greenhouse experiment, treatment groups of Helianthus were exposed to six varying intensities each of four acute stress applications: nutrient limitation, high soil salinity, heat, and simulated herbivory. Leaves formed during the onset of stress and post-stress were sampled to measure leaf traits; changes in plant fitness were estimated through total plant biomass and the time of first flowering. Results from statistical analyses show a variety of significant effects that stress applications had on plant growth and LES traits. Our findings explore the possibility of achieving off-axis LES trait combinations through salt-induced trait plasticity, and if further studies are needed to reassess the rigidity of the spectrum.

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<p><strong>ABSTRACT</strong></p> <p>As plants are sessile organisms, detecting the presence of neighboring plants and exhibiting competitive behavior to acquire limiting resources is crucial. One of the ways plants respond to belowground competition is by allocation to fine roots in order to acquire the limited resources. However, this phenotypic plasticity can be costly as it assigns resources away from reproduction. Being able to recognize the relatedness of one′s neighbours and preferentially compete with strangers is a beneficial trait that can minimize the costs of competition with relatives and increases inclusive fitness. Many studies have looked at the association between resource availability and competition in plants while others have observed kin recognition in several plants species. However, no one has yet studied the effect of resource availability on kin recognition in plants. Here, I looked at root architecture to test if there is an association between kin recognition and nutrient availability in <em>Cakile edentula</em>.</p> <p>I found that the root system architecture is highly plastic and complex, showing variable responses to neighbour identity signals and resource availability. The results from the four experiments demonstrate that the responses of <em>C. edentula </em>to neighbour relatedness are dependent on nutrient availability. Additionally, this study also indicates that kin recognition in <em>C. edentula</em> does not require root contact; instead it occurs through a signal found in soluble compounds excreted from plants, possibly root exudates, as observed in <em>Arabidopsis thaliana</em> <em>(</em>Biedrzycki et al. 2010).</p> <p>In conclusion, this study provides novel findings regarding the dynamics of root behavior in response to nutrient availability and the relatedness of neighbours.</p> / Master of Science (MSc)

Animals display considerable phenotypic variation in their mating traits, and this variation can have important consequences for the evolution of dimorphic traits between the males and females within a species. In chapter 1, I outline the current state of our understanding of plasticity in reproductive phenotypes, and argue that more work needs to be done to connect the gap between plasticity in mating traits and the outcomes of sexual conflict. Across my four data chapters, I used the fruit fly as a model organism in series of experiments that attempt to better understand how plasticity in mating traits influences the fitness outcomes of both males and females. In chapter 2, I experimentally manipulated the outcome of a fighting experience, and found that males who win a previous fight have higher precopulatory reproductive success, but losers perform better in post-copulatory areas. In chapter 3, I manipulated the amount of competition that a male experiences and found that females mated to males who experience competition produce more early-life offspring but live shorter lives compared to females mated to males that experience no competition. In chapter 4, I manipulated the intensity of sexual conflict that a female experiences and found that males mated to females who experience high conflict have lower pre- and post-copulatory reproductive success compared to males mated to females who experience low conflict. In chapter 5. I manipulated the degree of sexual aggression that a female experiences, and found that females that experience harassment and mating from a male that displays high sexual aggression is subsequently less choosy compared to females that experience a less aggressive male. Finally, in chapter 6, I discuss the significance of my results as they relate to the evolution of reproductive traits in males and females. / Dissertation / Doctor of Science (PhD) / Considerable phenotypic variation exists both within and across species. Within species, one source of this variation is phenotypic plasticity, the ability for an individual to alter its phenotype based on environmental influences. When it comes to sex, both males and females in many species exhibit striking variation in their reproductive behaviour as a result of plasticity. However, the causes and consequences of this variation are not well understood. Throughout my doctoral dissertation, I used the fruit fly as a model to explore how various social experiences such as fighting, competition, sexual harassment, and mating shape the subsequent reproductive behaviour of males and females, and quantified the evolutionary consequences of this variation. The results of my studies have important implications for understanding the evolution of various behavioural strategies such as aggression and mate choice.

Thesis (MSc (Botany and Zoology))--Unkiversity of Stellenbosch, 2009. / Phylogeographic genetic structure has been documented for a number of southern African terrestrial taxa. Information regarding geographic population genetic structuring in multiple taxa, with differing life histories, can provide insights into abiotic processes such as vicariance. A fragment of the cytochrome b mitochondrial DNA gene of a plains-dwelling species, Otomys unisulcatus, was sequenced and analysed. Two closely related geographic assemblages were found. The first assemblage (lowland group) contains populations from both the eastern and western parts of the species range, and the second comprises populations from the Little Karoo (central group). The lowland group was shown to be in a state of population expansion after a relatively recent mitochondrial DNA (mtDNA) coalescence, while the genetic signature of the central assemblage was characterized by more genetic diversity indicative of an older lineage/genetic refuge. Areas of higher elevation (namely mountain ranges) appeared to be the main factor limiting gene flow between these two groups. Aridification cycles due to glacial maximum periods probably resulted in increased dispersal leading to the widespread distribution of common haplotypes throughout the lowland group. Morphological variation in skull shape and size has been shown to follow environmental clines in some rodents. Geometric morphometric analyses on the ventral and dorsal views of the craniums of O. unisulcatus were utilised to test whether the population groupings obtained in the genetic analyses would be recovered by morphometric analyses. In addition, it was also investigated which of the environmental factors investigated influenced skull shape and size. The genetic groupings were not recovered for either the cranial shape or size. Size variation in the females correlated positively with annual rainfall, and so by proxy with habitat productivity, indicating that females which inhabited areas with lower rainfall would be larger. The significant relationship between females’ centroid sizes and rainfall was thought to be as a result of the increased nutrient requirement by this gender in the production of offspring. The males did not show a significant correlation between any of the environmental variables and centroid size. There was a significant difference between the skull shapes of the genders, further verifying the sexual dimorphism in the species. Three major clusters were found (according to cranium shape) using a Two-Block Partial Least Squares Analysis (2B-PLS), which relate to the biome boundaries within the species’ range. Variations in shape were attributed to the varying needs for strong masticatory muscles resulting from differing diets. The skull shapes of specimens occurring along the escarpment were intermediate between the first two clusters. Cranial shape in the male dorsal view dataset was significantly correlated with the environmental variables block, possibly due to the much lower minimum temperature in the Sutherland population (a population which was not included in the female analyses). It was concluded that differing diets of individuals in the respective biomes influenced the shape of the cranium of both genders. The sexual dimorphism in the cranium shapes may be as a result of the females digging tunnels (using their teeth) underneath the stick nests. Otomys unisulcatus show high levels of phenotypic plasticity throughout the range and it thus appears that the species can adapt fast to the different environmental variables.

The Extended Evolutionary Synthesis (EES) is currently emerging as a theoretical alternative to the Modern Synthesis (MS) in which to frame evolutionary observations and interpretations. These alternative frameworks differ fundamentally in their understanding of the relative roles of the genotype, phenotype, development and environment in evolutionary processes and patterns. While the MS represents a gene-centred view of evolution, the EES instead emphasizes the interactions between organism, development and environment. This novel theoretical framework has generated a number of evolutionary predictions that are mutually incompatible with the equivalent of the MS. While research and empirical testing has begun on a number of these in a neontological context, the field of palaeontology has yet to contribute meaningfully to this endeavour. One of the reasons for this is a lack of methodological approaches capable of investigating relevant evolutionary patterns in the fossil record. In this thesis morphometric methods capable of providing relevant data are developed and employed in the analysis of Cambrian fossils. Results of these analyses provide empirical support for the process of evolution through phenotypic plasticity and genetic assimilation hypothesized by the EES. Furthermore, theoretical revision to the species concept in a palaeontological context is suggested. Finally, predictions of the EES specific to the fossil record are made explicit and promising directions of future research are outlined.

Animals and plants in temperate regions must adapt their life cycle to pronounced seasonal variation. The research effort that has gone into studying these cyclical life history events, or phenological traits, has increased greatly in recent decades. As phenological traits are often correlated to temperature, they are relevant to study in terms of understanding the effect of short term environmental variation as well as long term climate change. Because of this, changes in phenology are the most obvious and among the most commonly reported responses to climate change. Moreover, phenological traits are important for fitness as they determine the biotic and abiotic environment an individual encounters. Fine-tuning of phenology allows for synchronisation at a local scale to mates, food resources and appropriate weather conditions. On a between-population scale, variation in phenology may reflect regional variation in climate. Such differences can not only give insights to life cycle adaptation, but also to how populations may respond to environmental change through time. This applies both on an ecological scale through phenotypic plasticity as well as an evolutionary scale through genetic adaptation. In this thesis I have used statistical and experimental methods to investigate both the larger geographical patterns as well as mechanisms of fine-tuning of phenology of several butterfly species. The main focus, however, is on the orange tip butterfly, Anthocharis cardamines, in Sweden and the United Kingdom. I show a contrasting effect of spring temperature and winter condition on spring phenology for three out of the five studied butterfly species. For A. cardamines there are population differences in traits responding to these environmental factors between and within Sweden and the UK that suggest adaptation to local environmental conditions. All populations show a strong negative plastic relationship between spring temperature and spring phenology, while the opposite is true for winter cold duration. Spring phenology is shifted earlier with increasing cold duration. The environmental variables show correlations, for example, during a warm year a short winter delays phenology while a warm spring speeds phenology up. Correlations between the environmental variables also occur through space, as the locations that have long winters also have cold springs. The combined effects of these two environmental variables cause a complex geographical pattern of phenology across the UK and Sweden. When predicting phenology with future climate change or interpreting larger geographical patterns one must therefore have a good enough understanding of how the phenology is controlled and take the relevant environmental factors in to account. In terms of the effect of phenological change, it should be discussed with regards to change in life cycle timing among interacting species. For example, the phenology of the host plants is important for A. cardamines fitness, and it is also the main determining factor for oviposition. In summary, this thesis shows that the broad geographical pattern of phenology of the butterflies is formed by counteracting environmental variables, but that there also are significant population differences that enable fine-tuning of phenology according to the seasonal progression and variation at the local scale. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Increasing temperatures resulting from climate change have within recent years been shown to advance phenological events in a large number of species worldwide. Species can differ in their response to increasing temperatures, and understanding the mechanisms that determine the response is therefore of great importance in order to understand and predict how a warming climate can influence both individual species, but also their interactions with each other and the environment. Understanding the mechanisms behind responses to increasing temperatures are however largely unexplored. The selected study system consisting of host plant species of the Brassicaceae family and their herbivore Anthocharis cardamines, is assumed to be especially vulnerable to climatic variations. Through the use of this study system, the aim of this thesis is to study differences in the effect of temperature on development to start of flowering within host plant species from different latitudinal regions (study I), and among host plant species (study II). We also investigate whether different developmental phases leading up to flowering differ in sensitivity to temperature (study II), and if small-scale climatic variation in spring temperature influence flowering phenology and interactions with A. cardamines (study III). Finally, we investigate if differences in the timing of A. cardamines relative to its host plants influence host species use and the selection of host individuals differing in phenology within populations (study IV). Our results showed that thermal reaction norms differ among regions along a latitudinal gradient, with the host plant species showing a mixture of co-, counter- and mixed gradient patterns (study I). We also showed that observed differences in the host plant species order of flowering among regions and years might be caused by both differences in the distribution of warm days during development and differences in the sensitivity to temperature in different phases of development (study II). In addition, we showed that small-scale variations in temperature led to variation in flowering phenology among and within populations of C. pratensis, impacting the interactions with the butterfly herbivore A. cardamines. Another result was that the less the mean plant development stage of a given plant species in the field deviated from the stage preferred by the butterfly for oviposition, the more used was the species as a host by the butterfly (study IV). Finally, we showed that the later seasonal appearance of the butterflies relative to their host plants, the higher butterfly preference for host plant individuals with a later phenology, corresponding to a preference for host plants in earlier development stages (study IV). For our study system, this thesis suggest that climate change will lead to changes in the interactions between host plants and herbivore, but that differences in phenology among host plants combined with changes in host species use of the herbivore might buffer the herbivore against negative effects of climate change. Our work highlights the need to understand the mechanisms behind differences in the responses of developmental rates to temperature between interacting species, as well as the need to account for differences in temperature response for interacting organisms from different latitudinal origins and during different developmental phases in order to understand and predict the consequences of climate change. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p>

Comprendre quels mécanismes contrôlent la variabilité phénotypique et comment ces mécanismes influencent et contraignent la divergence interspécifique est un objectif important en biologie de l'Evolution. Dans cette thèse, nous avons essayé d'étudier comment l'histoire phylogénétique, la génétique, l'environnement, et le développement influencent l'évolution d'une structure morphologique complexe, en utilisant la mandibule de la souris domestique comme modèle.Afin d'étudier les processus qui contrôlent la variation phénotypique, des analyses de génétique quantitative ont été réalisées sur un pedigree obtenu à partir des individus sauvages d'une population de la souris domestique. Les descendants ont été divisés en deux, l'un suit un régime alimentaire dur et l'autre un régime alimentaire mou, pour que l'effet de la plasticité phénotypique puisse être considérée. On montre que le développement et les contraintes épigénétiques pourraient changer l'architecture génétique des traits morphologiques dans une population. En outre, les résultats suggèrent que la plasticité phénotypique pourrait être adaptative dans certaines conditions environnementales, mais pas dans d'autres.Ensuite, on a utilisé la mandibule de la souris domestique pour étudier les patrons de l'évolution morphologique des populations de cette espèce dans un contexte phylogéographique. Les résultats suggèrent que la divergence morphologique chez la souris domestique a suivi la différenciation génétique. On a aussi trouvé que la variation morphologique a augmenté au cours de l'expansion des sous-espèces sans qu'une convergence significative n'accompagne l'évolution vers le commensalisme avec l'homme. Finalement on a déterminé si l'hypothèse d'évolution de la mandibule sous l'effet de la dérive génétique peut expliquer la diversification morphologique au cours de la divergence et d'expansion de la souris domestique. Les résultats rejettent cette hypothèse et plaident en faveur d'autres forces évolutives telles que la sélection.Nos résultats, dans leur ensemble, montre une origine multifactorielle de la variation et permettent de mieux comprendre la diversification morphologique des populations et des sous-espèces de la souris domestique. / A major goal of evolutionary biology is to understand which mechanisms monitor phenotypic variation and how this variation can generate species diversity. In this thesis we tried to investigate how phylogenetic, genetic, environmental, and development influence the evolution of a complex morphological structure using house mouse mandible as a model.In order to study the processes monitoring phenotypic variation, quantitative genetic analyses were performed on a pedigree of wild captured specimens of house mouse. The progenies were divided into two groups followed two different diets (soft and hard), so that the effect of phenotypic plasticity can be regarded. We show that developmental and epigenetic factors could influence the genetic architecture of morphological traits in a population. Moreover, the results suggest that phenotypic plasticity might be adaptive in some environmental conditions but not in the others.We then used the house mouse mandible in order to study the patterns of morphologic evolution of the populations of this species in a phylogeographic context. Our results show that morphological divergence in the house mouse was followed the genetic differentiation. We also found that morphological variation was increased during the expansion of house mouse subspecies without a significant convergence due to commensalism with human. Finally, we investigated whether the hypothesis of genetic drift could explain the morphological diversification during the divergence and expansion of the house mouse. The results reject this hypothesis and argue for the interfering of other evolutionary forces like selection.Our results, all in all, show a multifactorial origin for phenotypic variation and permit us to better understand the morphological divergence of the population of the subspecies of house mouse.