Using Patterns of Genetic Diversity to Detect the Signal of Supplemental and Restorative Stocking Among Native Brook Trout Populations

The dramatic decrease in the range of Brook trout (Salvelinus fontinalis) combined with the historic use of hatchery-reared brook trout for supplemental and restorative stocking underscores the need to recognize the evolutionary relationship among stream populations.  A suite (N=13) of microsatellite DNA markers has been surveyed of allelic variation in over 13,000 fish from 370 collections comprising the species’ native range.  This survey identified evolutionary relationships among populations, yielded a wide range of allelic diversity, demonstrated high levels of genetic differentiation at all hierarchical levels studied (individual to watershed), and documented similar levels of differentiation among collections within drainages and among collections between drainage basins.  Retrospective monitoring (i.e., coalescent simulations) of S. fontinalis populations has illuminated previously undetected demographic histories (e.g., supplemental or restorative stocking; bottlenecks) and shed light on past and future evolutionary trajectories of populations at previously intractable scales.  The demographic history of each defined population is being determined through estimates of time (T; in generations) to the most recent common ancestor.  This analysis also allows determination of the demographic trend of each population (i.e., increasing or decreasing effective population size; (r)), and provides a robust estimate of the current effective population size (Ne) for each population.  The working assumption being - populations with greater T values have persisted longer and are more likely to be adapted to the physiological and immunological challenges of their current environment.  In the absence of a defined suite of adapted genes, populations with greater T and Ne values would therefore serve as the more adaptable populations for use in restoration efforts.