Complex population history affects admixture analyses in nine-spined sticklebacks

Area of Science:

• Evolutionary biology
• Population genetics

Background:

• Introgressive hybridization is crucial for evolution but difficult to detect.
• Many population genetic analyses assume direct ancestry, which admixture violates, leading to biased results.

Purpose of the Study:

• To investigate complex population ancestry and gene flow in nine-spined sticklebacks (Pungitius pungitius).
• To understand the role of introgression in evolutionary processes and identify challenges in admixed population analyses.

Main Methods:

• Analysis of 888 whole-genome sequences from nine-spined sticklebacks.
• Examination of population ancestry patterns, gene flow, and introgression across Northern Europe.

Main Results:

• A complex pattern of multiple gene flow waves and introgression was identified across Northern Europe.
• Two distinct lineages showed different histories, with a wider-than-expected secondary contact zone and varied foreign ancestry.
• Freshwater isolates offered insights into intermediate evolutionary states.

Conclusions:

• The study provides a detailed view of Northern Europe's colonization history and the role of introgression.
• Hidden admixture and colonization history can significantly mislead estimations of admixture proportions and population split times.