Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Keyghobadi, Nusha


Understanding how much genetic diversity exists in populations, and the processes that maintain that diversity, has been a central focus of population genetics. The evolutionary processes that determine patterns of genetic diversity depend on underlying ecological processes such as dispersal and changes in population size. In this thesis, I examine the influence of dispersal and population dynamics on neutral and adaptive genetic variation in a naturally occurring network of populations of the alpine butterfly, Parnassius smintheus.

My first objective was to determine the combined consequences of demographic bottlenecks and dispersal on neutral genetic variation within and among populations. Using microsatellite markers, I genotyped samples collected from across the network over multiple years and tracked changes in genetic diversity and differentiation of populations across two documented bottlenecks. I also drew on long-term mark-recapture data characterizing population size and movement. I demonstrated that connectivity among populations rescues genetic diversity that is lost as a result of demographic bottlenecks. I also showed that levels and spatial patterns of genetic differentiation in the network change cyclically due to continual shifts in the relative dominance of genetic drift versus gene flow as populations fluctuate in size.

My second objective was to examine relationships between adaptive genetic variation and dispersal among populations. Using RNA sequencing, I compared gene expression patterns among individuals with differing dispersal histories. Individuals that had moved between patches (dispersers) upregulated genes involved in energy metabolism, muscle development and stress responses compared to individuals that remained in the same patch (non-dispersers). I also examined whether variation at a candidate locus, the gene encoding the metabolic enzyme phosphoglucose isomerase (PGI), is associated with dispersal and movement. I found that individuals possessing the rare allele at each of two non-synonymous Pgi single nucleotide polymorphisms were either more likely to disperse or dispersed longer distances.

My work demonstrates how population size fluctuations, dispersal, and landscape structure interact to shape levels and patterns of genetic diversity. My work also provides insight into how two key global change factors, habitat fragmentation and climate change, may work synergistically to erode genetic diversity in natural populations.