Genomic divergence between nine- and three-spined sticklebacks.

Area of Science:

• Evolutionary Biology
• Comparative Genomics
• Genomics

Background:

• The nine-spined stickleback (Pungitius pungitius) is an emerging model organism in evolutionary biology, closely related to the well-studied three-spined stickleback (Gasterosteus aculeatus).
• Limited genomic resources have hindered research on the nine-spined stickleback's evolutionary differentiation.
• Comparative genomics requires robust genomic data for phylogenetic and evolutionary analyses.

Purpose of the Study:

• To expand genomic resources for the nine-spined stickleback through deep sequencing of brain and liver transcriptomes.
• To identify genes evolving under positive selection between nine-spined and three-spined sticklebacks.
• To discover genetic markers for differentiating ecotypes and for future population studies.

Main Methods:

• Deep sequencing of nine-spined stickleback (Pungitius pungitius) brain and liver cDNA libraries.
• Transcriptome assembly and annotation.
• Comparative analysis with three-spined stickleback (Gasterosteus aculeatus) genomes to identify orthologs and estimate substitution rates.
• Identification of genes under positive selection, microsatellites, and single nucleotide polymorphisms (SNPs).

Main Results:

• Generated nearly 8,000 assembled transcripts, with 3,091 identified as one-to-one orthologs to three-spined stickleback genes.
• Estimated synonymous substitution rate at 7.1 × 10(-9) per site per year.
• Identified 165 genes showing patterns of adaptive evolution and 47 SNPs differentiating ecotypes.
• Discovered 468 microsatellite markers for potential use in nine-spined stickleback genetic studies.
• Observed evidence of gene loss in nine-spined sticklebacks since divergence from three-spined sticklebacks.

Conclusions:

• Deep sequencing significantly increased gene sequences and microsatellite markers for the nine-spined stickleback.
• Identified genes exhibiting adaptive evolution between nine-spined and three-spined sticklebacks.
• Reported candidate genes potentially involved in marine vs. freshwater adaptation in nine-spined sticklebacks.
• Provided a valuable resource for future studies on ecological adaptation in sticklebacks.