Reduced gravity and muon flux absence affect Caenorhabditis elegans life history traits and viral infection

Environmental conditions fundamentally shape host-pathogen interactions, yet how multiple extreme abiotic stressors combine to influence infection outcomes remains poorly understood. Organisms evolved under specific gravitational and radiation regimes; deviations from these conditions —whether in extreme terrestrial environments or beyond Earth— may alter immune function and pathogen replication. In this study, we investigated the effects of reduced gravity and lowered muon flux on Orsay virus infection in the nematode Caenorhabditis elegans . We employed a fully factorial experimental design, examining how each factor, alone and in combination, influences physiological traits and viral load. While below-background radiation radically affected viral accumulation dynamics, reduced gravity had a minor effect. Both factors significantly impacted reproduction and morphology, with some effects magnified by viral infection. These results reveal how even partial modifications of Earth-like gravity and radiation levels can alter pathogen–host interactions. By integrating experimental observations with mathematical modeling, we show that these environmental stressors primarily affect prezygotic reproductive processes and modulate viral replication through distinct and sometimes antagonistic mechanisms. Although this work does not encompass the full complexity of space environments, where cosmic radiation includes high-energy protons and heavy ions, it provides insight into how adjustable models of reduced gravity and radiation can advance our understanding of biological adaptation beyond standard terrestrial conditions.