The study of natural populations from contrasting environments has greatly enhanced our understanding of ecological-dependent selection, adaptation and speciation. Cases of parallel evolution in particular have facilitated the study of the molecular and genetic basis of adaptive variation. This includes the type and number of genes underlying adaptive traits, as well as the extent to which these genes are exchanged among populations and contribute repeatedly to parallel evolution. Yet, surprisingly few studies provide a comprehensive view on the evolutionary history of adaptive traits from mutation to widespread adaptation. When did key mutations arise, how did they increase in frequency, and how did they spread? In this issue of Molecular Ecology, Van Belleghem et al. () reconstruct the evolutionary history of a gene associated with wing size in the salt marsh beetle Pogonus chalceus. Screening the entire distribution range of this species, they found a single origin for the allele associated with the short-winged ecotype. This allele seemingly evolved in an isolated population and rapidly introgressed into other populations. These findings suggest that the adaptive genetic variation found in sympatric short- and long-winged populations has an allopatric origin, confirming that allopatric phases may be important at early stages of speciation.
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