Complex Patterns of Hitchhiking Mutation Load Among Stickleback Populations

Area of Science:

• Evolutionary genetics
• Population genetics
• Genomics

Background:

• Positive selection drives beneficial alleles to high frequency, potentially causing linked deleterious alleles to hitchhike.
• Low recombination rates and population size influence the sweep of linked deleterious mutations.
• Threespine stickleback exhibit repeated adaptation to freshwater, providing a model for studying hitchhiking effects.

Purpose of the Study:

• To investigate the impact of hitchhiking on mutation load in threespine stickleback.
• To estimate mutation load in low-recombination genomic regions, including inversions and the Eda haplotype.

Main Methods:

• Analysis of mutation load in specific genomic regions associated with adaptation.
• Examination of inversions and the Eda haplotype for accumulated deleterious alleles.
• Assessment of deviations from Hardy-Weinberg equilibrium in stickleback populations.

Main Results:

• Some evidence suggests an increased accumulation of deleterious alleles in one inversion.
• Two other inversions did not show this increased accumulation of deleterious alleles.
• Inversions showed deviations from Hardy-Weinberg equilibrium, with an excess of homozygotes observed in several populations.

Conclusions:

• Hitchhiking may contribute to mutation load in specific low-recombination regions during adaptation.
• The impact of hitchhiking on mutation load can vary across different genomic regions, such as inversions.
• Observed deviations from Hardy-Weinberg equilibrium indicate non-random mating or selection pressures within these populations.