Data from: Evidence for adaptive phenotypic differentiation in Baltic Sea sticklebacks

The evidence for adaptive phenotypic differentiation in mobile marine
species remains scarce, partly due to the difficulty of obtaining
quantitative genetic data to demonstrate the genetic basis of the observed
phenotypic differentiation. Using a combination of phenotypic and
molecular genetic approaches, we elucidated the relative roles of natural
selection and genetic drift in explaining lateral plate number
differentiation in threespine sticklebacks (Gasterosteus aculeatus) across
the entire Baltic Sea basin (ca. 392 000 km2). We found that phenotypic
differentiation (PST = 0.213) in plate number exceeded that in neutral
markers (FST = 0.008), suggesting an adaptive basis for the observed
differentiation. Since a close correspondence was found between plate
phenotype and genotype at a QTL (STN381) tightly linked to the gene
(Ectodysplasin) underlying plate variation, the evidence for adaptive
differentiation was confirmed by comparison of FST at the QTL (FSTQ =
0.089) with FST at neutral marker loci. Hence, the results provide a
comprehensive demonstration of adaptive phenotypic differentiation in a
high gene flow marine environment with direct, rather than inferred,
verification for the genetic basis of this differentiation. In general,
the results illustrate the utility of PST – FST – FSTQ comparisons in
uncovering footprints of natural selection and evolution, and add to the
growing evidence for adaptive genetic differentiation in high-gene flow
marine environments, including that of the relatively young Baltic Sea.