Genomic mechanisms and consequences of diverse postzygotic barriers between monkeyflower species.

This article focuses on the genomic mechanisms and consequences of postzygotic reproductive barriers between two naturally hybridizing monkeyflower species, *Mimulus cardinalis* and *M. parishii*. Using dense genetic linkage maps and recombinant inbred lines (RILs), the study identifies a major reciprocal translocation between Chromosomes 6 and 7 in *M. cardinalis* that causes severe underdominant pollen sterility and persistent heterozygosity across generations. Additionally, a novel two-locus Dobzhansky–Muller genic incompatibility causing sex-independent gametophytic (haploid) lethality was discovered between loci on Chromosomes 4 and 8, eliminating specific hybrid genotypic classes without affecting pollen viability or number. These findings reveal complex and persistent chromosomal and genic incompatibilities that shape hybrid fertility, transmission ratio distortion, and linkage disequilibrium, providing insight into the genomic architecture of reproductive isolation and speciation in this model plant system.