Rare jackpot individuals drive rapid adaptation in Threespine Stickleback

Area of Science:

• Evolutionary Biology
• Genomics
• Ecology

Background:

• Recombination is traditionally viewed as key for adaptation by assembling beneficial alleles.
• The transporter hypothesis suggests recombination drives parallel adaptation in Threespine Stickleback.
• Understanding rapid adaptation mechanisms is crucial for evolutionary studies.

Purpose of the Study:

• To investigate the genomic dynamics of rapid parallel adaptation in Threespine Stickleback during freshwater transition.
• To identify the genetic mechanisms facilitating swift adaptation to new environments.
• To assess the role of recombination versus other factors in rapid adaptation.

Main Methods:

• Whole genome sequencing of an evolutionary time-series of Threespine Stickleback.
• Analysis of genomic data to track allele frequency changes.
• Biological kinship analyses to infer mating patterns and genetic contributions.

Main Results:

• Rapid freshwater adaptation was facilitated by 'jackpot carriers' with large, pre-existing blocks of adaptive alleles.
• Mating involving jackpot carriers rapidly increased the frequency of adaptive alleles.
• The population overcame a severe bottleneck, potentially aided by inbreeding reducing genetic load.

Conclusions:

• Very rapid adaptation in this stickleback system was primarily driven by the inheritance of large adaptive haploblocks, not recombination.
• The identified mechanism highlights the importance of standing genetic variation and specific individuals in swift evolutionary responses.
• Inbreeding may have played a role in purging deleterious alleles post-bottleneck, facilitating population recovery.