A lifetime of attrition: post-genomic analyses of ecological and evolutionary processes in nematode - vertebrate systems.

Virtually every species of terrestrial, freshwater and marine vertebrate is parasitized by nematodes (roundworms). Nematode infections exhibit persistent infection and re-infection throughout the life of a host, with strong sex, age and season effects on intensities of infection. These parasites therefore constitute an important component of the environment of vertebrates and affect the fitness of individuals and the dynamics of populations. There is now a timely opportunity to apply new methods from genomics to explore the ecological and evolutionary consequences of vertebrate-nematode interactions in the natural environment. Such work holds great promise but extending genomics from the bench-top to natural populations also presents significant challenges. In particular, the variation between individuals that makes research in natural populations so important also makes it difficult to apply some genomics methods, such as high throughput gene expression (microarray) analyses. Our response to these challenges is to build a consortium based around three well-characterised vertebrate - nematode systems, the Soay sheep and Teladorsagia circumcincta, the red grouse and Trichostrongylus tenuis and the brown rat and Strongyloides ratti. We will use a series of approaches ranging from microarray studies within laboratory experiments that mimic the wild situation, through to microarray studies on individuals living in wild populations subject to experimental manipulations. As a result, we hope to learn from each other, and demonstrate to the research community, just how far these new methodologies can be applied to natural populations in situ. In the process, we expect to generate a trained group of workers with the skills to develop the field more widely in the UK. Work within the consortium will explore a set of related questions that, in combination, allow us to address two broad objectives that are crucial to advancing our understanding of host-parasite ecology and evolution: (1) To dissect and quantify the link between the genetic basis of host-parasite interactions and the population biology of hosts and parasites. Infection is a process that acts on individuals but impacts on the dynamics of populations; through the effects of infection on the growth, survival and reproduction of individuals. Equally, the density of a population will impact on the level of competition between individuals for food or mates and consequently on the condition of individuals and their susceptibility to infection. The key challenge now is to understand how individual processes of infection influence, and are influenced by, the population biology of hosts and parasites. (2) To examine the origins and maintenance of genetic diversity in host and parasite populations. Within a population, individual hosts exhibit genetic differences in their susceptibility to infection. Equally, populations of parasitic nematodes are genetically variable with consequences for the persistence and transmission of infection. The key challenges to be addressed now are to identify regions of vertebrate and nematode genomes where genetic diversity is maintained through the continued interaction between both antagonists, the consequences of this genetic diversity and the selective processes by which this diversity is maintained.