Baecklund, Tristan Mackenzie

Heterogeneous environments impose discordant selective pressures on natural populations, where disparate biotic/abiotic factors and variable population connectivity, yield mosaic patterns of genetic variation on the landscape. The ability to maintain or change genetic mosaics of populations becomes key to persistence, as species increasingly need to adapt to rapidly changing environmental and human-associated selective pressures. Specifically, infectious diseases can impose strong and rapid selective pressures on populations, where anthropogenic disruptions of co-evolutionary patterns and altered distributions of hosts and pathogens exacerbate disease risk. Genomic tools provide means to evaluate disease-associated impacts on the genetic landscape of host populations and facilitate implementation of informed conservation efforts. In this thesis, I evaluate disease dynamics in: 1) a long-standing arctic rabies/arctic fox (Vulpes lagopus) system affected by influxes of red fox (V. vulpes), and 2) an invasive bat pathogen system, where the North American introduction of Pseudogymnoascus destructans (Pd) has had variable impacts on bat species and populations. In these systems, signatures of host selection were estimated from temporal and spatial shifts in allelic diversity within genomic regions associated with immune response, highlighting different host mechanisms to enzootic and invasive diseases. In the arctic rabies/fox system, pathogen variants did not influence red fox local disease responses, reflecting more recent expansions of this host to Arctic regions. In contrast, arctic fox revealed genomic patterns consistent with long-term, co-evolutionary processes. In Pd/bat systems, genomic evidence supported the hypothesis that eastern small-footed bats (Myotis leibii) were inherently resistant or tolerant to Pd, the causative agent of white-nose syndrome (WNS). In contrast, WNS-impacted little brown bat (M. lucifugus) populations had varied genomic impacts subsequent to strong selective sweeps from disease. My research illustrates how immunogenetic profiling, in context of demographic processes inferred from neutral genetics, enhances understanding of the varied impacts of changing disease landscapes on host populations/species; insights relevant to other host-pathogen systems. Building on this thesis, future explorations of low coverage genomes, host-imposed reciprocal selection, and impacts on methylation, transcriptomic and proteomic patterns associated with shifts in genetic diversity, would enable more holistic understanding of the geographic mosaics within these disease systems.

Author Keywords: Disease Dynamics, High-throughput Sequencing, Immune System, Natural Selection, Population Genetics, Reduced Representation Sequencing