Seascape Genomics and Phylogeography of the Sailfish (Istiophorus platypterus)

Permeable phylogeographic barriers characterize the vast open ocean, boostinggene flow and counteractingpopulation differentiation and speciation of widely distributedand migratory species. However, many widely distributedspecies consists of distinct populations throughout their distribution, evidencing that our understanding of how the marine environment triggers population and species divergence are insufficient. The sailfish is a circumtropical and highly migratory billfish that inhabits warm and productive areas. Despite its ecological and socioeconomic importance as a predator and fishery resource, the species is threatened by overfishing, requiring innovative approaches to improve their management and conservation status. Thus, we presenteda novel high-qualityreference genome for the species and applied a seascapegenomics approach to understand how marine environmental features may promote local adaptation and how it affects gene flow betweenpopulations. We delimit two populations between the Atlantic and Indo-Western Pacific oceans and detect outlier loci correlated with sea surface temperature, salinity, oxygen, and chlorophyll concentrations. However, the most significant explanatory factor that explains the differences between populations was isolation by distance. Despite recent population drops, the sailfish populationsare not inbred. For billfishesin general, genome-wideheterozygosity was found to be relatively low compared to other marine fishes, evidencingthe need to counteractoverfishing effects. In addition, in a climate change scenario, management agencies must implement state-of-the-art sequencing methods, consider our findings in their management plans, and monitor genome-wide heterozygosity over time to improve sustainable fisheries and the long-term viability of its populations.