No description available.

No description available.

No description available.

Natural organisms are infected by many different parasites, and as a consequence, hosts have evolved a wide range of defences to cope with them. Resistance may be conferred through mechanisms that reduce susceptibility to infection ('avoidance') or increase the rate of clearance ('recovery'). Other forms of resistance reduce the deleterious effects of infection ('tolerance'), or inhibit the parasite's growth ('control'). In addition to these innate forms, hosts may also benefit from immunological memory ('acquired immunity'). The evolution of resistance is expected to be costly in terms of other life history traits. In the presence of such 'trade-offs', the host population may evolve towards an evolutionarily stable strategy (ESS) that balances the costs and benefits of resistance. Another possibility is that a process of evolutionary branching occurs, leading to polymorphism of distinct strategies. Parasites also show adaptation to their hosts and have generally not evolved to be avirulent. Again, this is the result of trade-offs between virulence and other aspects of life history. Often, a higher transmission rate is attained at the cost of increased virulence. This thesis uses a mathematical modelling approach to examine hostparasite interactions. The first part considers the evolutionary dynamics of quantitative host resistance and parasite traits, employing fitness expressions constructed using the techniques of adaptive dynamics. The second part examines the population dynamics of host-parasite interactions; in particular, how different assumptions about the nature of the transmission process may affect the dynamics.

No description available.

Natural organisms are infected by many different parasites, and how these parasites interact with each other has important ecological and evolutionary implications. This study is to understand how organisms with different transmission strategies effect the evolution of each other. Parasites that transmit vertically benefit from the host having a high reproductive rate whilst hosts that transmit horizontally are not affected by host reproduction. Some horizontal parasites may reduce host fecundity to benefit their own replication within the host. Therefore there will be clear conflict between vertically and horizontally transmitted parasites. The evolution of traits such as vertically transmitted `protection' and `sabotage' are likely to be costly in terms of other life history traits. In the presence of such `trade-offs,' the parasite population will evolve towards the evolutionarily stable strategy (ESS) that balances the costs and benefits of these strategies in response to a horizontally transmitted parasite. The ecology of the interaction of vertically and horizontally transmitting parasites is also examined. Further to this, field data is used to construct a model of two horizontally transmitting parasites, a pathogen and a parasitoid that occur on the Orkney Isles. We demonstrate how each of them, and both in combination, may have a large effect on resultant dynamics of winter moth, Operophtera brumata, populations.

No description available.

No description available.

Resistance to parasites is advantageous for most organisms but investing limited resources into defence depends on the selection pressure involved and the nature and magnitude of costs involved. The evolutionary interactions between hosts and their parasites have received much attention but the effect of intracellular parasites in such systems is far less understood. Microsporidia are intracellular parasites of vertebrates and invertebrates that have gained prominence both as a pathogen and a potential biocontrol agent. This thesis investigates evolution of resistance against intracellular parasites and the associated trade-offs in Drosophila melanogaster and Tubulinosema kingi system. Stage-specific susceptibility of the host to T. kingi infection and stage-specific within-host parasite proliferation; host tissue specificity and the impact of T. kingi on host sex ratio were also investigated in this system. Immune responses of D. melanogaster to T. kingi infection were examined. Increased haemocyte density and phenoloxidase activity was observed in infected flies and a negative effect of nitric oxide on parasite density was observed. Five pairs of replicate D. melanogaster lines were used for experimental evolution of resistance to T. kingi. The within-host parasite density decreased significantly in selected lines indicating the evolution of resistance. The early fecundity and longevity of selected lines were significantly higher than of control lines when infected by T. kingi. Trade-offs associated with increased resistance against microsporidia was investigated. The evolved resistance was negatively correlated with fecundity both under normal and stressed conditions of the host; the selected lines were also poor larval competitors for scarce food resources. The haemocyte density and phenoloxidase activity in haemolymph of larvae from selected lines was higher than in control lines. The implications of these results are discussed in relation to other host-parasite systems and the possibility of using the system as a model insect-microsporidia system to explore ecological and evolutionary interactions.

Le mildiou de la vigne, causé par le pathogène Plasmopara viticola, est une maladie cryptogamique pouvant causer de sérieux dégâts sur les récoltes. Pour éviter ces pertes, il est nécessaire de recourir à des produits phytosanitaires. Outre leur coût financier, les questions sur la santé des viticulteurs et des populations vivant à proximité des vignobles, ainsi que la protection de l’environnement ne peuvent être ignorées. Cependant, toutes les variétés de vigne ne présentent pas la même sensibilité au pathogène. En effet, bien qu’elles soient moins appréciées pour leurs qualités organoleptiques, les variétés américaines sont résistantes à cette maladie. Les combiner par croisement variétal avec des espèces européennes peut constituer une alternative viable aux traitements antifongiques. Cependant, pour piloter effacement ces problèmes de sélection variétal, il est nécessaire de mieux appréhender la relation « hôte-pathogène ». C’est dans ce but que l’analyse par spectrométrie de masse a été employée sous différents aspects / Downy mildew, caused by the Plasmopara viticola pathogen, is a fungal disease which can induce serious harvest damages. To avoid these losses, it is necessary to use phytosanitary treatments. In addition to their financial cost, winegrower’s health issues and the environment protection cannot be ignored. However, all grapevine varieties do not present the same sensitivity to the pathogen. Indeed, despite of poor organoleptic qualities, American varieties are resistant to this disease. Combining them with European species by varietal crossing may be a viable alternative to these treatments. However, to lead efficiently these cross breeding programs, it is necessary to know more about the relationship "host-pathogen". In this context, analysis by mass spectrometry has been used under different aspects