Data from: Selection on the morphology-physiology-performance nexus: lessons from freshwater stickleback morphs

Conspecifics inhabiting divergent environments frequently differ in
morphology, physiology and performance, but the interrelationships amongst
traits and with Darwinian fitness remains poorly understood. We
investigated population differentiation in morphology, metabolic rate and
swimming performance in three-spined sticklebacks (Gasterosteus aculeatus
L.), contrasting a marine/ancestral population with two distinct
freshwater morphotypes derived from it: the ‘typical’ low-plated morph,
and a unique ‘small-plated’ morph. We test the hypothesis that similar to
plate loss in other freshwater populations, reduction in lateral plate
size also evolved in response to selection. Additionally, we test how
morphology, physiology, and performance have evolved in concert as a
response to differences in selection between marine and freshwater
environments. We raised pure-bred second generation fish originating from
three populations and quantified their lateral plate coverage, burst- and
critical swimming speeds, as well as standard and active metabolic rates.
Using a multivariate QST-FST framework, we detected signals of directional
selection on metabolic physiology and lateral plate coverage, notably
demonstrating that selection is responsible for the reduction of lateral
plate coverage in a small-plated stickleback population. We also uncovered
signals of multivariate selection amongst all bivariate trait combinations
except the two metrics of swimming performance. Divergence between the
freshwater and marine populations exceeded neutral expectation in
morphology and in most physiological and performance traits, indicating
that adaptation to freshwater habitats has occurred, but through different
combinations of traits in different populations. These results highlight
both the complex interplay between morphology, physiology and performance
in local adaptation, and a framework for their investigation.