Transient Microgeographic Clines during B Chromosome Invasion

Area of Science:

• Evolutionary biology
• Population genetics
• Genomics

Background:

• The near-neutral model predicts B chromosome invasion completion in tens of generations.
• Real-world B chromosome invasion dynamics in natural populations remain largely uncharacterized.
• Understanding B chromosome spread is crucial for evolutionary and genetic studies.

Purpose of the Study:

• To investigate the invasion process of B chromosomes in a natural grasshopper population (Eyprepocnemis plorans).
• To analyze changes in B chromosome frequency and distribution over a 35-year period.
• To test hypotheses regarding B chromosome drive and selection during invasion.

Main Methods:

• Longitudinal population sampling of Eyprepocnemis plorans over 35 years (three time points).
• Analysis of B chromosome frequencies and spatial distribution (cline analysis).
• Computer simulations to model genotypic frequency changes under different evolutionary pressures.

Main Results:

• B chromosome frequency significantly increased in the studied population over 35 years.
• A previously observed microgeographic cline in B chromosome frequency vanished as frequencies reached an upper limit.
• Simulations supported female-biased B chromosome drive and selection against individuals with high B chromosome loads.

Conclusions:

• B chromosome invasion involves transient geographic clines at the invasion front.
• The observed dynamics are consistent with meiotic drive in females and selection against B chromosomes.
• This study provides empirical evidence for B chromosome invasion dynamics predicted by theoretical models.