Testing evolutionary hypotheses for the long-term maintenance of balanced immunogenetic polymorphisms in a wildlife model
Lead Research Organisation:
UNIVERSITY OF EXETER
Department Name: Biosciences
Abstract
Infectious diseases are a major cause of morbidity and mortality in humans, livestock and wild animals. Although the immune system has evolved as a defence against infection and plays a key role in influencing host health and survival, it is not perfect, and substantial genetic variation in disease vulnerability is typically observed among hosts. To date it is not well understood why and how genetic variation in immune function is preserved over extended (i.e. evolutionary) timescales. Understanding the factors that maintain genetic variation in immune function within a species will tell us why vulnerability to infectious diseases is not eliminated by selection, why some populations are more susceptible to infectious diseases than others, and how environmental change and newly emerging diseases influence the costs and benefits associated with different immune gene variants, and thus affect immune system evolution.
In our project we will use wild bank voles, an exceptionally tractable wild rodent model that shows a distinct genetic polymorphism at an immune receptor involved in the defence against bacterial pathogens, to test why and how genetic variation in immune function is maintained in populations.
Hosts are typically exposed to a wide range of pathogens simultaneously. If being resistant to one pathogen comes at the cost of being susceptible to another, these diverse pathogen communities can maintain immune gene variation in host populations. Using next-generation sequencing technology, we will characterise entire microbial communities within voles to test if their genetic makeup influences pathogen-specific infection, either directly or indirectly by affecting their commensal microbes.
Alternatively, immune gene variation may be maintained because of a resistance - 'harm-to-self' trade-off. Although powerful immune responses are required to prevent or clear an infection, they may act as a double-edged sword and also cause 'harm-to-self'. To date it is not known if immune gene variants differ in the amount of collateral damage they cause when they are activated. By experimentally activating the immune system of voles that differ in their genetic makeup, we will test if immune gene variants that confer pathogen resistance also cause more collateral damage to the host.
Ultimately, these trade-offs can maintain genetic variation in immune function because they ensure that immune gene variants are not absolutely good or bad, but that their costs and benefits are dependent on either the host's external environment, or on intrinsic host characteristics, such as sex. We will experimentally test this by manipulating population density and pathogen infection risk in large outdoor enclosures and quantify survival and reproduction of males and females with different genetic makeup. This will allow us to test if the fitness outcomes of genetic variants are context-dependent.
The outcome of the project will be an improved understanding of the mechanisms and selective forces that contribute to the maintenance of genetic variation in immune function and disease vulnerability in natural populations, with broad cross-disciplinary implications for evolutionary biology, disease ecology, wildlife conservation, and human and animal health.
In our project we will use wild bank voles, an exceptionally tractable wild rodent model that shows a distinct genetic polymorphism at an immune receptor involved in the defence against bacterial pathogens, to test why and how genetic variation in immune function is maintained in populations.
Hosts are typically exposed to a wide range of pathogens simultaneously. If being resistant to one pathogen comes at the cost of being susceptible to another, these diverse pathogen communities can maintain immune gene variation in host populations. Using next-generation sequencing technology, we will characterise entire microbial communities within voles to test if their genetic makeup influences pathogen-specific infection, either directly or indirectly by affecting their commensal microbes.
Alternatively, immune gene variation may be maintained because of a resistance - 'harm-to-self' trade-off. Although powerful immune responses are required to prevent or clear an infection, they may act as a double-edged sword and also cause 'harm-to-self'. To date it is not known if immune gene variants differ in the amount of collateral damage they cause when they are activated. By experimentally activating the immune system of voles that differ in their genetic makeup, we will test if immune gene variants that confer pathogen resistance also cause more collateral damage to the host.
Ultimately, these trade-offs can maintain genetic variation in immune function because they ensure that immune gene variants are not absolutely good or bad, but that their costs and benefits are dependent on either the host's external environment, or on intrinsic host characteristics, such as sex. We will experimentally test this by manipulating population density and pathogen infection risk in large outdoor enclosures and quantify survival and reproduction of males and females with different genetic makeup. This will allow us to test if the fitness outcomes of genetic variants are context-dependent.
The outcome of the project will be an improved understanding of the mechanisms and selective forces that contribute to the maintenance of genetic variation in immune function and disease vulnerability in natural populations, with broad cross-disciplinary implications for evolutionary biology, disease ecology, wildlife conservation, and human and animal health.
