Genetic introgression among charr species in the Shiretoko Peninsula, Japan

Researchers have uncovered significant genetic introgression among charr species within the UNESCO World Heritage Site of Shiretoko Peninsula, Japan. Using environmental DNA (eDNA) metabarcoding, they found that up to 97.2% of non-Southern Asian Dolly Varden (SADV) mitochondrial DNA in 40 rivers could be attributed to introgression from White-spotted charr, despite the latter's absence in these regions. The study also identified a minor but notable proportion (up to 0.47%) of eDNA linked to Salvelinus malma, a species not native to Japan, suggesting an additional independent introgression event. These findings highlight the potential for eDNA metabarcoding to detect hidden evolutionary legacies in freshwater fish populations, particularly where conventional surveys are impractical. The research underscores the importance of cautious interpretation of mtDNA-based analyses in systems with frequent genetic exchange and provides valuable insights for conservation genetics.

Ozawa, T., Kanbe, T., Yatsuyanagi, T., & Araki, H. (2026). Genetic introgression among charr species in the Shiretoko Peninsula, Japan. Journal of Fish Biology, 109(3), 1800–1809. Portico. https://doi.org/10.1111/jfb.70558