Isolation by phenology synergizes isolation by distance across a continuous landscape

Area of Science:

• Population genetics
• Evolutionary biology
• Ecological genetics

Background:

• Pollen dispersal typically results in short-distance gene flow, promoting spatial population genetic structure.
• Quantitative genetic variance in flowering time influences temporal mating patterns, particularly concerning phenology loci.

Purpose of the Study:

• To investigate the synergistic effects of isolation by distance (IBD) and isolation by phenology (IBP) on population genetic structure.
• To determine how combined spatial and temporal isolation mechanisms influence genetic variance and differentiation.

Main Methods:

• An individual-based model was developed to simulate genotype frequencies at flowering time and neutral loci over multiple generations.
• Four mating schemes were simulated: panmixia, IBD only, IBP only, and a combination of IBP × IBD.
• The model tracked genetic variance, spatial clustering, and gametic disequilibrium within a uniform landscape.

Main Results:

• The combined IBP × IBD mating scheme resulted in spatial clustering of early-, mid-, and late-flowering genotypes, significantly increasing quantitative genetic variance.
• IBP alone moderately increased flowering time genetic variance without spatial clustering.
• IBD alone induced mild spatial structure in a neutral trait but did not alter its variance.
• The spatial correlation of neutral loci genotypes was twice as strong under IBP × IBD compared to IBD alone.
• IBP × IBD also induced gametic disequilibrium between neutral and flowering time loci, creating temporal structure.

Conclusions:

• The synergistic interaction of isolation by distance and isolation by phenology strongly promotes both spatial and temporal population genetic structure.
• This combined structuring of mating pools facilitates local genetic differentiation.
• The findings suggest a mechanism that would promote adaptation on smaller spatial scales.