Hybrid Fitness in Mimulus Aurantiacus var. Calycinus x Mimulus Aurantiacus var. Longiflorus

Authors: Jovana Simic, Rachel Pitt, Emma Rella, Josh Knecht, James Sobel

Field of Study: Science, Technology, Engineering, and/or Math

Faculty Mentors: James Sobel

Easel: 37

Timeslot: Midday

Abstract: Hybridization between diverging populations offers a unique opportunity to study genetic interactions that contribute to speciation. When hybridization occurs between partially isolated populations, selection against low-fitness hybrids counteracts gene flow that eludes prezygotic barriers.The Dobzhansky-Muller model proposes that negative epistasis between divergent loci generates low-fitness hybrids without requiring parental populations to cross a fitness valley. Previous work evaluating seedling growth in Mimulus auraticaus var. calycinus X M. aurantiacus var. longiflorus provided evidence for negative interactions between these recently diverged genomes. This research expanded on this work by adding back-crosses, along with F1s, F2s, and the parents. Seed weight, seed area, and germination timing were measured. F1 hybrids were at least as fit as parental lines, while F2 and backcross generations exhibited reduced fitness, suggesting that heterozygous x heterozygous interactions significantly reduced hybrid viability. These findings provide evidence for negative epistatic interactions, highlighting the complexity of hybrid fitness landscapes.