Mutation Load in Sunflower Inversions Is Negatively Correlated with Inversion Heterozygosity

Area of Science:

• Evolutionary genetics
• Population genetics
• Genomics

Background:

• Recombination is vital for adaptation and purging mutations.
• Chromosomal inversions can suppress recombination, potentially leading to mutation accumulation.

Purpose of the Study:

• Investigate recombination patterns, transposable elements, and coding sequence evolution in sunflowers.
• Analyze inversion effects on phenotypes to test for overdominance.
• Determine how inversion polymorphism impacts deleterious mutation load.

Main Methods:

• Genome-wide analysis of recombination, transposable elements, and mutations in 1,445 sunflower individuals.
• Genotyping of nine segregating inversions within three sunflower species.
• Phenotypic trait analysis to assess inversion genotype effects.

Main Results:

• Negative correlation between retrotransposon abundance/deleterious mutations and recombination rates across genomes.
• Inversions showed minimal increase in mutations, except for stop codon mutations in large/rare inversions.
• Little evidence of inversion overdominance for fitness-related traits.
• Higher deleterious load in polymorphic inversion populations compared to monomorphic ones.

Conclusions:

• Low frequency of inversion heterozygotes, driven by divergent selection, explains the lack of mutation accumulation.
• Inversions promote adaptive divergence with gene flow by acting as recombination modifiers.
• Inversions facilitate adaptation while minimizing deleterious mutation load in wild sunflower populations.