Polar ecosystems harbor highly divergent DNA viruses underrepresented in current reference databases

Viruses dominate global ecosystems, yet their genetic diversity remains incompletely represented in current reference databases. To address this knowledge gap, we conducted a latitudinal comparison of environmental DNA viromes spanning marine and terrestrial habitats across polar north and south and temperate regions. Viral genes were reconstructed from metagenomic datasets and their phylogenetic divergence assessed relative to database reference sequences. Three consistent patterns emerged. First, reconstructed sequences were substantially more divergent than database references, underscoring the limited coverage of existing viral sequence collections. Second, polar viromes exhibited significantly higher within-region divergence, with south polar assemblages consistently the most distinct and north polar divergence varying by biome. Third, these patterns were found to be robust to potential reconstruction artifacts; all datasets underwent identical processing, and divergence inflation was observed exclusively in polar samples. Together, these results challenge the canonical latitudinal diversity gradient in viral communities and identify polar environments as major reservoirs of uncharacterized viral diversity, with implications for biodiversity baselines under global climate change.