Islands in the stream: Genetic analysis of brook trout population structure and demographics reveals a high degree of population fragmentation and prodigious differentiation within and among streams

We have collaborated in an extensive survey of allelic variation in over 10,000 brook trout (Salvelinus fontinalis) from 270 collections comprising the species’ native range.  Coalescence-based demographic analyses provided previously undetected demographic histories (e.g., time to most recent common ancestor (T), population trajectory (r), and effective population size (N)) and evolutionary relationships among populations.  Findings indicate that the individual stream or collections within should be considered the fundamental unit of management (contrary to the current paradigm).  These research findings create somewhat of a management conundrum - Does genetic divergence observed among brook trout reflect adaptive significance (natural selection) or is this indicative of drift-induced differentiation?  Given that natural selection ultimately acts on the genetic variation underlying character variation, identifying the genes associated with parallel evolutionary changes among recently diverged lineages is essential to uncovering candidate genes implicated in adaptive phenotypic variance.  Determining whether fisheries managers should focus their resources on identifying/characterizing genetic relatedness (e.g., everything from morphological comparisons to gene expression profiling) or determining the number of fish needed to establish population persistence is a high priority research need (i.e., a new research paradigm).  We will discuss the degree to which research and management paradigm shifts may be warranted.