A central question to evolutionary biology is how separate species form. Speciation is thought to occur after one population splits into two that then diverge over time. Divergence between the populations can be slowed by some evolutionary forces, such as when migrants share genes between populations, but it can be reinforced by others.  One reinforcing force is local adaptation; when a migrant from one population is not adapted to the environment of the second population, it may not reproduce successfully and share its genes.  To study the conflicting forces of migration and local adaptation, we assayed populations of two subspecies of Mexican wild maize, the teosinte, with genome-wide DNA.  Our results suggest that the two subspecies have diverged genetically despite continuous gene migration between them and that their divergence has been fueled by adaptation to contrasting temperatures and soil phosphorus concentrations. Genetic divergence between the two subspecies is particularly marked for five chromosomal regions that are enriched for genes that contribute to local adaptation. These regions have low recombination rates between populations, suggesting they could be chromosomal inversions. We conclude that Mexican teosintes may be undergoing the initial steps of the process of speciation, despite ongoing gene flow.

Aguirre‐Liguori JA, Gaut BS, Jaramillo‐Correa JP, et al. Divergence with gene flow is driven by local adaptation to temperature and soil phosphorus concentration in teosinte subspecies (Zea mays parviglumis and Zea mays mexicana). Mol Ecol. 2019;28:2814–2830. https://doi.org/10.1111/mec.15098