Age-Dependent Immune Defense Against <em>Beauveria bassiana</em> in Long- and Short-Lived <em>Drosophila Populations</em>

Aging in sexually reproducing organisms is shaped by the declining force of natural selection after reproduction begins. In Drosophila melanogaster, experimental evolution shows that altering the age of reproduction shifts the timing of aging. Using the Drosophila Experimental Evolution Population (DEEP) resource, which includes long- and short- lived populations evolved under distinct reproductive schedules, we investigated how immune defense against Beauveria bassiana changes with age and evolved lifespan. We tested survival post-infection at multiple ages and examined genomic differentiation for immune-related genes. Both population types showed age-related declines in immune defense, but long- lived populations consistently exhibited greater defense at all ages. Genomic comparisons revealed thousands of differentiated loci, yet no enrichment for canonical immune genes or overlap with gene sets from studies of direct selection for immunity. These results suggest that enhanced immune defense can evolve alongside extended lifespan, likely via general physiological robustness rather than traditional immune pathways. Our findings challenge the assumption of a trade-off between longevity and immunity and demonstrate the utility of experimentally evolved populations for dissecting the genetic architecture of aging and immune defense against Beauveria bassiana.