The genetic basis of traits associated with the evolution of serpentine endemism in monkeyflowers.

This article investigates the genetic architecture underlying adaptive divergence and prezygotic reproductive isolation between the serpentine soil endemic *Mimulus nudatus* and its widespread relative *Mimulus guttatus* within the *Mimulus guttatus* species complex. Using quantitative trait locus (QTL) mapping of F2 hybrids, the study found that both few large-effect and many small-effect loci contribute to differences in life history, floral, and leaf traits associated with serpentine adaptation and reproductive isolation. Notably, QTL for adaptive traits (e.g., leaf size, developmental timing) and reproductive isolating traits (e.g., flower size, flowering time) overlapped more than expected by chance, with allelic effects generally aligned with species divergence, suggesting genetic correlations via pleiotropy or linkage may facilitate speciation across soil boundaries. The findings support a role for consistent directional natural selection in shaping these traits and highlight that alleles from the serpentine endemic tend to be recessive, potentially reflecting its demographic history or types of mutations fixed during divergence.