Abstract
Understanding how eco-evolutionary processes and environmental factors
drive population differentiation and adaptation are key challenges in
evolutionary biology and of relevance for biodiversity protection.
Differentiation requires at least partial reproductive separation, which
may result from geographic isolation (allopatry), isolation by distance
(IBD), environment (IBE), adaptation (IBA), and time (IBT). We
investigate how ecological and evolutionary processes influence genetic
diversity and structure in 11 populations of pike (Esox lucius)
using Restriction-site Associated DNA sequencing (RADseq). Study
populations represented three ecotypes (freshwater, anadromous, and
brackish water resident) along a latitudinal gradient (54.9 - 63.6 °N).
Genetic diversity and structure were investigated both for the full
RADseq dataset (5993 loci) and for an adaptive subset consisting outlier
loci. Both neutral and adaptive processes influenced genetic structure,
and their contributions differed between allopatric and sympatric
populations, and also within and among ecotypes. Signatures of neutral
processes were pronounced among geographically isolated freshwater
populations, likely reflecting long time since divergence combined with
low gene flow. For sympatric populations, ecotype (anadromous versus
resident) and geography influenced both neutral and adaptive genetic
structure, consistent with IBE. Outlier analyses pointed to a role of
selection associated with salinity and temperature, consistent with IBA.
Results provide rare evidence that separate analyses of neutral and
adaptive loci can help illuminate how different, potentially
interacting, processes jointly contribute to shaping spatiotemporal
patterns of biodiversity. It is argued that data on adaptive rather than
neutral genetic variation should inform management and policy
development.