Restricted (Penn State Only)
Weathers, Thomas Casey
Graduate Program:
Wildlife and Fisheries Science
Doctor of Philosophy
Document Type:
Date of Defense:
December 14, 2018
Committee Members:
  • John Edward Carlson, Dissertation Advisor
  • John Edward Carlson, Committee Chair
  • Timothy Lee King, Committee Member
  • Jesse R Lasky, Committee Member
  • Ephraim Mont Hanks, Outside Member
  • Matthew A Kulp, Special Member
  • Population genetics
  • Genetic differentiation
  • Isolation
  • Fragmentation
  • Riverscape genetics
  • Conservation
Many range-restricted species, particularly mountaintop species, are often the first groups in which entire species experience extinction due to range contractions and perturbations. Rear-edge, lower latitude, salmonid populations often occupy fragmented habitats and may in turn exhibit more pronounced signatures of isolation than higher latitude conspecifics. Therefore, rear-edge populations present significant conservation challenges to biologists interested in identifying and maintaining ecological and evolutionary processes within and among such populations. Brook Trout (Salvelinus fontinalis), the only endemic salmonid to southern Appalachia, are rich in ecologically and evolutionarily interesting traits such as multiple life history forms, broad latitudinal and elevational distribution, and prodigious neutral genetic differentiation. Causes of continual Brook Trout population and range declines include overharvest, acid precipitation, habitat degradation, competition with non-native species, and climate change. Such declines have led to the increased isolation of many populations of Brook Trout. In the absence of gene flow many isolated populations of Brook Trout may exhibit rapid genetic drift or inbreeding, thus resulting in subsequent losses of adaptive potential. Consequently, there is considerable demand for the implementation of restoration programs that maximize population recovery and resilience of wild Brook Trout. As such, resource managers must plan for an evolutionary future for such a trust species. While the current paradigm of conservation places emphasis on recognition and protection of irreplaceable evolutionarily distinct lineages, the precise and accurate delineation of populations must become a priority. Once populations are identified the best strategy for future conservation may be to enhance connectivity via restoration or translocation efforts rather than protecting specific genotypes. Elucidating spatial clusters of Brook Trout is critical to their conservation, particularly regarding unprecedented environmental change. Therefore, I have combined informative microsatellite data with riverscape genetics approaches to assess whether functional (meta)population assemblages exist among rear-edge populations of Brook Trout sampled across southern Appalachia in the following research chapters. My research elucidates the effects of isolation and fragmentation on Brook Trout genetic and phenotypic (i.e., morphometric and meristic) differentiation, whether neighboring populations exhibit enough gene flow to warrant being considered metapopulations, and the effect of potential barriers to gene flow upon subsequent metapopulation dynamics and genetic diversity. My research largely suggests that rear-edge populations of Brook Trout exhibit extensive neutral genetic differences and appear to be prodigiously isolated. My findings provide biologists a reference when setting management and conservation priorities and may foster more aggressive efforts focused on restoring connectivity among many populations of rear-edge Brook Trout. Further, by demarcating population and subpopulation clusters across riverscapes I provide resource managers information needed to enhance future Brook Trout conservation outcomes. I sought to document existing patterns of genetic variation within and among populations of Brook Trout and then translate my results into an approachable format for managers to access for future management and conservation decision making and to further encourage managers to implement population genetic monitoring programs. My work supports that non-native trout removals combined with habitat restorations could improve connectivity and enhance the outlook for many fragmented populations of wild, native brook trout across southern Appalachia. Moreover, it is my hope that the results from these studies can be used by Brook Trout biologists to select local restoration source stocks used to potentially bolster the effectiveness of different conservation strategies (i.e., founder translocations and genetic rescue).