Digest: Hybrid incompatibilities and introgression in wild monkeyflowers.

How are alleles that are detrimental to fitness maintained in natural populations? Zuellig and Sweigart (2018a) find that alleles from a two-locus hybrid incompatibility system segregate at considerable frequencies in two species of monkeyflowers, suggesting that despite providing a fitness cost, these alleles remain polymorphic as a consequence of gene flow between the two species. The system provides the potential to understand the evolutionary trajectory of hybrid incompatibilities and their role in speciation.