Nearly every organism has to cope with harmful infections from pathogens. Organisms can respond by either killing invading pathogens ('resistance') or by reducing the damage caused by pathogens ('tolerance'). Among animals, resistance has been well studied, but relatively little is known about the causes and consequences of tolerance. This project focuses on a bacterial disease that emerged in the mid-1990s in a common backyard songbird, the house finch, causing rapid population declines. This infection causes severe tissue damage, in the form of conjunctivitis (pink-eye). 'Tolerance' is likely an important way to mitigate this harmful infection. Because the disease reached parts of the house finch range at distinct times, the proposed work uses comparisons among geographically separated finch populations to uncover 1) how quickly 'tolerance' evolves in response to a novel pathogen, 2) the gene expression mechanisms important for tolerance, and 3) the consequences of 'tolerance' for disease spread within flocks. This project also crafts innovative means to communicate its scientific findings with the public. The researchers have joined a global network of science enthusiasts by founding a program that hosts monthly public events where short presentations by scientists or other experts are separated by musical or artistic interludes. Multiple events will feature results from this project. In addition, through a graduate-level course at Virginia Tech this project will train young scientists and educators to design their own programs that enhance public engagement with science.
Infectious diseases are among the most powerful and pervasive selective forces on the planet. Because vigorous resistance mechanisms, such as inflammatory immune responses in vertebrates, can reduce host fitness by damaging an animal's own tissues, selection should favor some degree of tolerance of infection across diverse hosts. To date, however, work on animals has focused almost exclusively on resistance. By combining molecular techniques and inter-population comparisons, this project directly advances our knowledge of three of the most critical, open issues in the study of animal tolerance: how selection shapes this host strategy following disease emergence, the immune mechanisms underlying tolerance, and the consequences of host tolerance for pathogen transmission. The work utilizes a number of techniques to assess immune responses rarely tested in non-model organisms (e.g., expression of songbird cytokine genes through qPCR and expression of myriad other host genes through RNA-seq). In addition, this project uses experimental epidemics to link differences in individual host responses with pathogen transmission dynamics. Through this combination of comparative, molecular, and experimental techniques, this project integrates the concept of tolerance across levels of biological organization, linking the causes and consequences of this defense strategy from molecules to populations, all in a naturally occurring host-pathogen system. Ultimately, this work will significantly advance knowledge of how tolerance of infection arises in animals and how this host response impacts the dynamics of pathogen epidemics.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
