DNA Viruses Generally Show Higher Phylogenetic Divergence in Polar Regions and Remain Underrepresented in Current Databases

Abstract

Viruses dominate ecosystems worldwide, yet the broader phylogenetic space they occupy remains poorly represented in current reference databases. How environmental viral divergence varies across latitudes and biomes, and to what extent current references capture it, remains largely unquantified. This thesis addresses this research gap through a global-scale comparative analysis of divergence in viral sequences reconstructed from environmental DNA metagenomes, spanning marine and terrestrial biomes from pole to pole. The metagenomes (n = 180) were sampled equally across six biome-latitude treatments (marine and terrestrial × north, equatorial, and south regions; n = 30 each). Two principal patterns emerged in the analysis. First, reconstructed viral sequences exhibited significantly higher divergence than database sequences, indicating that existing references still fail to capture much of the global viral phylogenetic diversity. Second, most polar viromes displayed statistically higher divergence relative to non-polar regions, with Antarctic sequences consistently higher, whilst the Arctic Ocean was a prominent outlier. Collectively, these findings generally identify polar regions as reservoirs of highly divergent viral sequences and underscore the need to refine current databases by expanding sampling efforts. Since all samples were analysed using the same workflow, any methodological biases would have affected all treatments uniformly, rendering artefactual explanations unlikely. This thesis also establishes a reproducible framework alongside a temporal reference for global viral divergence patterns, particularly in the polar regions where rapid climate-change-driven ecological shifts are anticipated to be much more disruptive.