Decoding Local Adaptation in the Exploited Native Marine Mussel Mytilus chilensis: Genomic Evidence from a Reciprocal...

Local adaptations are important in evolution as they drive population divergence and preserve standing genetic diversity essential for resilience under climate change and human impacts. Protecting locally adapted populations is essential for aquaculture species. However, high larval connectivity and frequent translocations challenge this in Chilean blue mussel (Mytilus chilensis) aquaculture, a world-class industry in Chiloé Island. This study examined local adaptations in two ecologically distinct natural beds, Cochamó (northernmost inner sea of Chiloé) and Yaldad (southernmost tip), through a 91-day reciprocal transplant experiment and genomic evidence. Cochamó mussels grew faster in their native environment (0.015 g/day) than Yaldad (0.004 g/day), though growth declined upon transplantation. Mussels transplanted within and between beds displayed distinctive adaptive transcriptomic responses, with differentially expressed genes involved with immune function, osmoregulation, metabolism, and cellular balance. Additionally, 58 known outlier SNPs mapped over the species' genome sequence were linked with adaptive genes involved with osmoregulation, oxidative stress, and oxygen management, revealing selection-targeted specific genome regions. This study highlights how translocations affect the adaptive genomic response of M. chilensis and the impact of local environments in counterbalancing its genetic connectivity, concluding that the genomic differences in natural beds should be monitored and conserved for sustainable aquaculture practices.