Genomic Insights into the Population Structure of Cetacean Top-Predators in the North Atlantic Ocean

Climate change is driving rapid shifts in marine species distributions, including northward expansions of temperate cetaceans into Arctic waters. Understanding how these shifts affect genetic connectivity is critical for defining effective management units. We conducted a genome-wide population-genomic analysis of three temperate cetaceans, long-finned pilot whales (Globicephala melas), Atlantic white-sided dolphins (Leucopleurus acutus), and white-beaked dolphins (Lagenorhynchus albirostris), to reassess population structure across the North Atlantic, including previously undersampled Greenlandic waters. Previous studies based on mitochondrial DNA, microsatellites, and ddRAD suggested contrasting patterns of structure, but were limited by uneven sampling or low genomic resolution. Our results confirm strong genetic differentiation between North Atlantic and Mediterranean pilot whales, alongside fine-scale west-to-east structuring within the North Atlantic and evidence of admixture. Atlantic white-sided dolphins show no significant population structure, supporting a panmictic North Atlantic population with low levels of inbreeding. In contrast, white-beaked dolphins form three distinct clusters, with Greenlandic individuals grouping within a western North Atlantic cluster alongside Canadian samples. We also detect elevated inbreeding among individuals from the North Sea and the waters surrounding the British Isles. These findings refine population boundaries across all three species and highlight the importance of genome-wide data for detecting subtle structure, with direct implications for conservation and management under ongoing climate-driven range shifts.