Graduate Thesis Or Dissertation
 

Trade-offs in a pathogen-rich world : genetic and maternal drivers of variation in costly resistance and immunity in African buffalo (Syncerus caffer)

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xp68km53q

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  • Disease acts as a powerful selective force in natural systems, driving the rapid evolution of resistance in the host. In the face of a myriad of pathogenic challenges in natural systems, hosts must balance the energetic needs of maintenance and reproduction with costly resistance mechanisms. In this dissertation I will (1) characterize Mycobacterium bovis (bovine tuberculosis (bTB)) resistance strategies in African buffalo (Syncerus caffer) and determine associated costs that lead to the maintenance of variation in host response, (2) identify putative mechanisms of bTB infection resistance, and (3) determine the effects of maternal rearing environment on calf survival, growth, and immune development. Here I demonstrate measureable costs of a highly heritable form of bTB resistance in free-ranging African buffalo. Buffalo able to delay infection to a later age show reduced condition throughout life and reduced survival following infection, but a higher overall reproductive rate. Taken together, the costs and benefits of infection resistance imply a “fast” life history strategy in these animals as they reproduce early, die after infection, and show evidence of investment in highly costly immunity to prevent infection with bTB. I also present evidence that variation in infection resistance is mechanistically tied to phagocyte activation, with measurable differences in IL-12 production among genotypes at a locus associated with a four-fold increase in bTB risk. Additionally, I reveal that milk fat content is highly conserved across mothers, but immune components of milk vary in a resource-dependent manner with mothers of higher condition, size, and age provisioning higher concentrations of immune-active constituents. However, although milk fat positively impacts calf survival, associations of immune components are less clear. Generally, lactoferrin (an anti-microbial peptide) and immunoglobulin G (IgG) in milk associated with higher growth rates, but lower immune function in the calf, especially before weaning. These findings agree with theoretical predictions that maternal passive immunity acts to ‘free-up’ neonatal energetic resources for growth. Taken together, this body of work elucidates the roles of genetic background and maternal effects on disease susceptibility and early health and immunity and represents a unique validation of previously proposed theoretical and laboratory work. Additionally, patterns in disease response and maternal provisioning identified here contribute to our overall understanding of resource partitioning in stochastic systems.
  • Keywords: evolutionary ecology, host-parasite, ecoimmunology
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