Population structure and local selection yield high genomic variation in Mimulus guttatus

Area of Science:

• Evolutionary Biology
• Genomics
• Population Genetics

Background:

• Mimulus guttatus exhibits local adaptation across western North America.
• Gene flow between populations impacts genetic diversity within and among demes.
• Understanding these dynamics is crucial for metapopulation genetic structure.

Purpose of the Study:

• To analyze whole-genome sequences from the Iron Mountain (IM) population and compare them with broader North American Mimulus samples.
• To investigate the effects of gene flow and local selection on genetic diversity and haplotype structure within a locally adapted population.

Main Methods:

• Whole-genome sequencing of 34 individuals from the Iron Mountain population and 22 individuals from across western North America.
• Analysis of intrapopulation polymorphism, Tajima's D, and haplotype structure.
• Application of a novel tree-based analytic method to assess genomic patterns.

Main Results:

• High levels of intrapopulation polymorphism (synonymous π = 0.033) were observed in the IM population.
• A significantly positive genomewide average for Tajima's D indicated intermediate allele frequencies, contrary to many species.
• A distinctive haplotype structure suggested significant gene flow from other Mimulus populations, with some evidence of local adaptation at specific loci.

Conclusions:

• The genomic patterns suggest successful gene flow of divergent immigrant genotypes into the IM population.
• A balance between local selection, limited dispersal, and metapopulation dynamics influences the genome.
• SNPs associated with chromosomal inversions show patterns indicative of local adaptation.