Pathogen-induced tension between ecological and evolutionary conservation priorities

Group Leader: Drew Harvell email: cdh5@cornell.edu

Rapporteur: Sonia Altizer email: saltizer@princeton.edu

Other participants: Peter Hudson, Priyanga Amarasekare, Per Arneberg, Armand Kuris

 

Disease transmission in single host populations or species will be influenced by genetic and ecological components of host population structure. Demographic variables that influence population structure and disease spread include local extinction-colonization dynamics and host dispersal in heterogeneous environments. Genetic heterogeneity in host resistance will also affect the invasion and persistence of disease, and may be particularly important in small, subdivided populations. Although evolutionary history can be difficult to infer from contemporary host-parasite systems, future population trajectories will be strongly modified by genetic processes acting on ecological time scales. Understanding the evolutionary potential of host populations in relation to disease is therefore vital to current conservation efforts. Our objectives focus on particular ecological and evolutionary factors that govern the spread and impact of pathogens in heterogeneous host populations, and understanding the conditions for which each of these priorities will be of overriding importance in developing conservation strategies.

In many species, ecological complications can affect the within-population dynamics of disease. We will review how metapopulation dynamics and habitat heterogeneity influence the invasion and persistence of pathogens. In particular, we will explore the interaction between local density dependence and host dispersal, and the likelihood that pathogens generate allee effects or host population crashes. We will also examine empirical patterns of disease spread associated with transmission foci and discuss their implications for controlling epidemics. Our ultimate goal is to understand how demographic or spatial structure influence host-parasite interactions, and apply this knowledge to conservation issues such as the design of reserves, consequences of habitat fragmentation, and invasion by novel pathogens.

Genetic heterogeneity in host resistance will also affect the invasion and persistence of disease, and may be particularly important in small, subdivided populations where genetic drift leads to inbreeding depression and reduced heterozygosity. Here we will review the consequences of genetic variation within and among host populations for disease dynamics. In particular, we will address the relative importance of inbreeding depression, costs of resistance, and the underlying genetic basis for resistance in determining disease prevalence and host-parasite coevolution. We will also examine empirical examples where genetic differences among populations contribute to geographical variation in parasite abundance and virulence.

Host resistance can be a rapidly evolving character in host pathogen interactions, and this evolutionary potential is vital to conservation efforts. We will review theoretical and empirical observations concerning the strength of parasites as selective agents in free-living host populations. Of particular importance are the predicted rates of evolution of resistance to pathogens, particularly in response to ecological changes that precipitate widespread epidemics. We will discuss the implications of genetic factors for managing threatened populations, including recommendations for captive breeding programs and managing threats from new or emerging diseases.