Resource availability and the evolution of host resistance to parasites: within individuals, trade-off shapes and the genetic basis of resistance

Context of the research
Recent epidemics continue to emphasise the importance of infectious disease such as SARS to human health and agricultural production. It is also clear that most if not all animals, plants and microbes are infected by a wide variety of infectious diseases. These diseases whether they are caused by bacteria, viruses or nematode worms often cause significant harm to their hosts. In particular they may shorten their life or reduce the number of offspring that the infected individual host can produce. As a consequence individuals have evolved a wide variety of ways of resisting infection. They can avoid becoming infected, recover more quickly or reduce the damage that the host causes them. Understanding what factors determine resistance is vital if we are to manage disease in natural and agricultural systems. In particular, in natural environments there is considerable variability in the resources that are available at any particular time in any given place. Since individuals have limited resources and they must allocate them to competing demands - such as the maintenance of body condition - such variation in resources is critical to the impact of disease. It is therefore important to understand the role that resources play in the evolution of resistance.

Aims and objectives
In order to understand the role that resources have on immunity it is necessary to carry out experiments where resources are altered. This requires the use of a model empirical system where the necessary control of resources can be achieved. We propose a set of detailed experiments using such a model based on an insect and its viral pathogen. First we will develop a number of genetic tools based on the advances in sequencing technology that have occurred in recent years. We will measure the genetic basis of the costs and benefits of immune function. Our approach is to control the breeding of the insect so that we can examine the immune function within families. This allows us to determine how much of the variation is due to relatedness and therefore genetics. By carrying out these experiments in different environments, we can work out how the nature of genetic variation changes under different circumstances. We will also look at how the immune response changes under different resource environments during the time course of the infection within single individuals. Finally we will allow evolution to occur in the laboratory under good and bad environments and see if the resistance that occurs comes about due to different mechanisms.

Potential applications and benefits
The fundamental application of this work is that it will help us to understand how immunity evolve. This can then reduce the harm that disease causes in natural systems and to people. In particular our results may enable us to predict how we can better manage disease through changes in diet. We will also have a better chance of predicting when and how the man made changes in the environment that are occurring may lead to disease outbreaks. Human activity is changing many environments and often leading to a reduction in the available resources for hosts. As such we need a better understanding of the implications of this to disease in order to manage and conserve natural resources. The laboratory model system that we use is a major agricultural pest and therefore our results also have the potential to help in its control.

Our proposal has the potential to make an impact within a wide range of different disciplines. We are addressing a phenomenon that is applicable to a wide range of infectious disease in human and agricultural as well as natural systems. As such we will aim to raise awareness of our work with ecologists and evolutionary biologists interested in disease, immunologists and parasitologists, insect physiologists, virologists, medical entomologists studying arbovirus transmission, epidemiologists and conservationists. Our approach is to develop a strong web presence with a dedicated website where data, scripts and results are presented in an accessible form for researchers from divers disciplines.

The proposed work will also have direct application in the development of novel control mechanisms for this important pest (Plodia interpunctella) other stored product pests and insect pests more widely. There is a clear need for new control agents of insects and viruses have considerable potential, but a lack of understanding of resistance mechanisms has contributed to the failure of a number of products to be commercialised. We have established a new collaboration with a commercial partner interested in the development of such novel controls. Our impact plan is to develop this relationship through meetings and the employment of short term RAs to establish knowledge gaps and determine a pathway to providing key information for product development.