Craniofacial morphology varies considerably between primate species with many aspects of structural variation occurring within the masticatory apparatus. These variations in masticatory fonn are frequently attributed to differences in diet however elucidating the relationship between masticatory form and function is complex. This study combines the techniques of shape analysis in a comparative study of the primate masticatory apparatus with three-dimensional biomechanical modelling of primate jaw mechanics. The relationship between masticatory form and function is investigated within a subfamily ofprimates, the Cercopithecinae. Species within this group display a range of masticatory forms, inhabit a wide range of environments, have varying diets and share close phylogenetic relationships making them an ideal group to investigate the relationship between structure and function. Using the techniques of geometric morphometrics a shape analysis was conducted in which variations within the masticatory forms of the Cercopithecinae were quantified. Functional predictions of observed shape differences were made and considered in light of known environmental and ecological factors with particular emphasis on dietary specialisations and fall back foods. The results of the shape analysis indicate that differences in body size, strata utilisation, and diet appear to play a major role in structuring adult morphological diversity within and among the Cercopithecinae. Many of the shape differences associated with an increased body size appear to reflect the selective pressures of increased predation risk, including increases in the length ofthe jaw and canine teeth. These morphological traits are associated with the production of a large gape and are hypothesised to be functional adaptations to the use of canines as weapons. Other major shape differences apparent between the Cercopithecinae were those associated with the proportion of leaves and fruit in the diet. The highly frugivorous Mandril/us species possessed features associated with increasing gape and retractile motions of the mandible ideal for incision of large fruits. By contrast the dietary specialist Theropithecus gelada possessed features associated with increasing the efficiency of food breakdown and muscle force production, necessary to process their more abrasive foodstuff (i.e. grasses).

No description available.

Bilateral symmetry is the simplest and most common type of symmetry in organisms and for this reason it has been extensively studied in many biological contexts. Geometric morphometrics is concerned with the quantification of morphological variation in organisms and has been specifically developed for studies of symmetry and asymmetry. Most studies of symmetry have focused on bilaterally symmetric structures (e.g., human faces). However, bilateral symmetry is not the only type of symmetry in biological shapes and other types of symmetry exist as well (e.g., radial symmetry in flowers). So far, there are no general methods for morphological analysis of these types of symmetry. Here, I propose a new and general approach for norphological analysis of structures with any type of symmetry. This framework combines the tools of geometric morphometries with a mathematical definition of symmetry. Depending on the type of symmetry under study, this method can separate a component of symmetric variation among individuals from one or more asymmetry components.

A number of problems concerned with the process of regeneration in lizards have been considered in this thesis. Various factors were found to influence the rate of tail regeneration in L. dugesii. In Anguis the rate of regeneration was always very low; reasons for this are discussed in the light of the histological appearances of the regenerate. An electron microscopical investigation of the normal skin of the tail has been presented; the features observed have been compared with those in other keratinising epithelia. The way in which the structure of the epidermis of regenerating tails differs from the normal condition is discussed with reference to the role of the epidermis in regeneration. The tails of embryo lizards have been shown to possess limited powers of regeneration; the inhibiting effects of the embryonic membranes are discussed. The process of healing of amputated embryonic limbs has been considered. The changes which occur in the limb stumps and digits of lizards after amputation have been described with reference to their almost complete lack of regenerative ability.

Aspects of the biology of foliage-fregenting Psocoptera were studied at Silwood Park, Ascot, Berkshire from Autumn 1965 to Spring 1965.These insects were considered especially in relation to the total arboreal psocid fauna and to their main habitat. i.e. the foliage of different tree species. Psocid samples from litter and from trees were taken concurrently and were counted and identified. Descriptions of the early stages and life histories of nine species are based on field and laboratory data. Several species were found only on some tree species and numbers of others showed large differences on different trees. Some of the factors that may influence the relative numbers of the same species of Psocoptera on different tree species were investigated. Counts of eggs on different tree species also revealed variations in psocid abundance. Aerial dispersal of Psocoptera was assessed with the aid of suction traps. The potential food supply of psocids on foliage of a range of tree species was compared at different times of the year and also with that consumed by psocids. The fecundity of several psocid species fed on foods from different trees was compared. Laboratory experiments showed that selection of oviposition site was related to characteristics of different leaf surfaces . The biology .of two groups of hymenopterous parasites of Psocoptera were examined, especially in relation to their fecundity and host specificity. A series of arthropods were identified as predators of psocids and their numbers on different species of trees were compared.

The prothoracic morphology of a wide range of Acalypterates has been examined, and is described in some detail. Conflicting terminologies for the various sclerites are discussed and a comprehensive system of nomenclature is proposed for them. The possible uses of prothoracic sclerites in Acalypterate systematics has been surveyed, leading to a detailed study of the probasisternum (or prosternum). The variability of the prosternum has been analysed, in an attempt to arrive at an understanding of the evolution of its shape and the relation between this and the evolution of Acalypterates. The methods by which it has been attempted to derive such information from modern forms are presented in full. The status and probable relationships of 23 Acalypterate families are discussed, comparing deductions made using prosternal shape with deductions based upon other characters. In conclusion it is suggested that variation in prosternal shape provides a reasonably reliable guide to Acalypterate inter-relationships, and could be especially useful in unravelling relations between families. Attention is drawn to the possible applications of methods used here in other studies, and to the differing information content of dimorphic and polymorphic taxonomic characters.

No description available.

A study is made of the general life history and behaviour of the larvae and adults of Pionea forficalis. Special emphasis is laid on oviposition and on the factors affecting fecundity. Investigations into the nature of diapause in P. forficalis and of the factors concerned with its inception and termination are described. These studies lead to a determination of the relative importance of genetic and environmental factors in the inception of diapause, and into its intensity as illustrated by family emergence distributions. An ecological appraisal of P. forficalis is made using data from the above investigations and from estimates of seasonal abundance based on field sampling. These are related to the characteristics of Brassica crop management to obtain a basis for the determination of the incidence and general abundance of this insect.

Histological examinations of the central nervous system of Dysdercus fasciatus revealed neurosecretory activity throughout nymphal and adult development. Four types of neurosecretory cells, A, B, C and D cells, were described in the pars intercerebralis but largely A cells were observed in other sites of the brain and ventral ganglia. Neurosecretion was not found in the embryo. In the first instar, only A and D cells were observed; B and C cells appeared in subsequent stadia and in adults. The numbers of each cell type increased during development. Two modes of secretion are postulated; neurohaemal release from the corpora cardiaca into the aorta, and direct trans-port through extended axons embedded in the aortal walls to the fat body. Secretory cycles based on histological changes in cell and nuclear volumes and appearance of the neurosecretory product were observed over the following four time intervals of different durations. Stress conditions lasting several hours induced immediate activity in A, B, C and D cells which increased as stress was prolonged. Median neurosecretory cell breis from stressed insects accelerated heart beat. Over twenty-four hours, the onset of light coincided with maximum secretion in A, B and C cells but D cells were unaffected over the daylight period. Peak oxygen consumption coincided with maximum activity of A, B and C cells and implants of median neurosecretory cells and the corpora allata accelerated oxygen consumption. In each instar, maximum synthesis and release in A, B and C cells occurred just before the Mid-intermoult; D cells synthesized continuously but secreted only at the moult. Conelation was observed between neurosecretory activity and changes in the prothoracic glands, epidermis and oxygen consumption of each stadium. The necessity of the median neurosecretory cells for growth and metamorphosis was demonstrated. In adults, maturation of the ovaries in mating females coincided with periods of maximum secretory activity of A, B and C cells. Injection of cysteine-S35 into fourth instar nymphs revealed continuous synthesis and release throughout the stadium of the secretory product in A, B and C cells. Rates and amounts of uptake varied and were characteristic for each cell type. Peak uptake coincided with histologically-defined periods of maximum secretory activity. It is concluded that histological and physiological criteria are useful and complementary methods of assessing neurosecretory activity. The view that all histologically-recognisable cell types occurring in Dysdercus are distinct forms rather than phases of one another is discussed, and the definition of a neurosecretory cell evaluated.

In their struggle for life, plants can employ sophisticated strategies to defend themselves against potentially harmful pathogens and insects. One mechanism by which plants can increase their level of resistance is by intensifying the responsiveness of their immune system upon recognition of selected signals from their environment. This so-called priming of defence can provide long-lasting resistance, which is based on a faster and/or stronger defence reaction upon pathogen or pest attack (Figure 1). Priming can target various layers of induced defence that are active during different stages of the plant-attacker interaction. Although it has been known for several years that priming can enhance the effectiveness of different plant defence responses, the underpinning molecular mechanisms have remained poorly understood. The main aim of the work described in this thesis was to explore the mechanisms controlling the establishment and long-term maintenance of defence priming. Chapter describes the early signalling events leading to broad-spectrum defence priming after treatment with the chemical agent BABA, whilst the subsequent experimental chapters focus on long-term maintenance of defence priming (Figure 1). Chapter 2 describes the isolation and characterization of the Impaired in J1.ABA induced Immunity (ibi 1) mutant, which was selected for loss of BABA-induced resistance against the oomycete Hyaloperonospora arabidopsidis. Map-based cloning of fBll revealed that this gene encodes a pathogen-inducible aspartyl tRNA synthetase, which mediates esterification of L-aspartic acid to its cognate tRNA. The results in Chapter 2 suggest that IBI I exhibits an additional non-canonical function as a receptor of BABA and a native regulator of basal resistance. Importantly, t.he work described in this Chapter provides evidence that the stress response triggered by relatively high concentrations of BABA is under separate genetic control than BABA-induced priming of broad-spectrum defence. This outcome provides exciting scope to exploit IBI I-dependent resistance in crops, particularly against plant diseases that are difficult to control by fungicides or single resistance genes. Recently, studies have emerged suggesting that long-lasting priming phenomena are controlled by epigenetic regulatory mechanisms. Priming of defence genes has been associated with modifications of histone proteins at defence-related gene promoters, which may facilitate access of the transcriptional machinery to gene promoters. Chapter 3 focuses on the durability of BABA-induced resistance in Arabidopsis. Treatment of 5 day-old Arabidopsis seedlings resulted in protection against H arabidopsidis and Pseudomonas syringae that lasted up to 4 weeks after BABA treatment. This long-lasting component is under the control of the NON-EXPRESS OR OF PR GENES 1 (NPRl) protein and is associated with priming of SA-inducible genes. Analysis of mutants in chromatin remodelling processes revealed that long-lasting induced resistance by BABA requires regulation by post-translational modification of Histone 3 Lysine 9 (H3K9) and H2A.Z occupancy. Conclusive evidence for an epigenetic basis of defence priming came very recently from independent laboratories across the world. Chapter 4 describes one of these studies and shows that defence priming can be transmitted to following generations from diseased Arabidopsis plants after fitness-reducing levels of disease by the bacterial pathogen P. syringae pv. tomato DC3000 (PstDC3000). Compared to progeny from control-inoculated plants (Cl), progeny from diseased plants (PI) expressed significantly higher levels of basal resistance to the oomycete pathogen H arabidopsidis and PstDC3000. In addition, the findings in this chapter demonstrate that PI plants are primed to respond to exogenously applied SA, but are repressed in their responsiveness of lA-inducible genes, which correlated with enhanced susceptibility to the necrotrophic fungus Alternaria brassicicola. Interestingly, the transgenerational SAR phenotype of PI plants is associated with permissive and repressive chromatin modifications at SA- and lA-inducible gene promoters, respectively. Finally, phenotypic analysis of the drmldrm2cmt3 mutant, which is impaired in non-CpG methylation, suggests an important role for this plant-specific form of DNA methylation in the transmission oftransgenerational SAR. Chapter 5 serves as an Addendum to the work described in the previous chapter, and describes further analysis of mutants in RNA-directed DNA methylation (RdDM) for their ability to express transgenerational SAR upon repeated infection by PstDC3000. The results indicate that transgenerational SAR is regulated by the RdDM pathway and likely transmitted through hypomethylation of genomic DNA at CpHpG sites. How all the various molecular and epigenetic mechanisms of priming relate to each other remains unknown and will require further research, which is a critical first step towards large-scale exploitation of the phenomenon in sustainable agriculture. In Chapter 6, I describe how long-lasting induced resistance can be applied to protect the crop Solanum lycopersicum (tomato). The costs (plant growth reduction) and benefits (effectiveness and durability of the induced resistance) of different resistance-inducing treatments have been studied. Seed treatment with jasmonic acid (lA) or f3-aminobutyric acid (BABA) rendered long-lasting protection that was not associated with major costs. However, the consistency of the induced resistance was rather low and was cultivar-dependent. Also, the incubation of seeds for prolonged periods with lA provided long-lasting protection against the necrotrophic pathogen B. cinerea with no adverse effects on seed germination or plant growth. Treatment of tomato seedlings with lA and BABA resulted in a more pronounced resistance response that lasted up to 5 and 6 weeks after the treatment, respectively. However, the disease protection upon these application methods was associated with residual fitness costs. Finally, the possibility of transgenerational induced resistance in tomato was investigated. The results in Chapter 3 set the basis to integrate long-lasting induced resistance in conventional strategies of tomato protection (Chapter 6). Food security is one of the most challenging issues faced by humanity in this century, and is likely to become further aggravated by climate change that can render agricultural lands less suitable for crop production. Consequently, there is a pressing need to improve the efficiency of sustainable food production, including intensification of durable crop protection strategies. Integration of long-lasting induced resistance into existing disease management schemes would allow lower energy costs to reach similar levels of disease protection. My Ph.D project has uncovered different regulatory mechanisms of long-lasting indu~ed resistance based on priming of defence. Future research will be necessary to narrow down the mechanisms by which genetics and epigenetics mediate priming of defence. I hope that these new insights will help to optimise the efficiency of robust and durable induced resistance in plants.