biostudies-literatureSandstedt GDNIGMS NIH HHSNational Science Foundation600-613https://www.ebi.ac.uk/biostudies/studies/S-EPMC7987689biostudies-literatureUnknown75(3)Species are often defined by their ability to interbreed (i.e., Biological Species Concept), but determining how and why reproductive isolation arises between new species can be challenging. In the Mimulus tilingii species complex, three species (M. caespitosa, M. minor, and M. tilingii) are largely allopatric and grow exclusively at high elevations (>2000 m). The extent to which geographic separation has shaped patterns of divergence among the species is not well understood. In this study, we determined that the three species are morphologically and genetically distinct, yet recently diverged. Additionally, we performed reciprocal crosses within and between the species and identified several strong postzygotic reproductive barriers, including hybrid seed inviability, F1 hybrid necrosis, aEvolution; international journal of organic evolutionEvolution of multiple postzygotic barriers between species of the Mimulus tilingii complex.PMC7987689‐18561801350935T32 GM007103DEB‐Sandstedt GDWu CASweigart ALfalseEvolution of multiple postzygotic barriers between species of the Mimulus tilingii complex.Species are often defined by their ability to interbreed (i.e., Biological Species Concept), but determining how and why reproductive isolation arises between new species can be challenging. In the Mimulus tilingii species complex, three species (M. caespitosa, M. minor, and M. tilingii) are largely allopatric and grow exclusively at high elevations (>2000 m). The extent to which geographic separation has shaped patterns of divergence among the species is not well understood. In this study, we determined that the three species are morphologically and genetically distinct, yet recently diverged. Additionally, we performed reciprocal crosses within and between the species and identified several strong postzygotic reproductive barriers, including hybrid seed inviability, F1 hybrid necrosis, a2021-01-01T00:00:00Z2021 Mar2026-05-31T05:01:04.722Z2025-02-19T01:53:46.346ZS-EPMC79876893304400610.1111/evo.14105