Latitudinal Clines in Climate and Sleep Patterns Shape Disease Outcomes in <i>Drosophila melanogaster</i> Infected by <i>Metarhizium anisopliae</i>

Major latitudinal clines have been observed in <i>Drosophila melanogaster</i>, a human commensal that originated in tropical Africa and has subsequently dispersed globally to colonize temperate habitats. However, despite the crucial role pathogens play in species distribution, our understanding of how geographical factors influence disease susceptibility remains limited. This investigation explored the effects of latitudinal clines and biomes on disease resistance using the common fly pathogen <i>Metarhizium anisopliae</i> and 43 global <i>Drosophila melanogaster</i> populations. The findings revealed correlations between disease resistance and latitudinal gradients of sleep duration, temperature, and humidity. Although enhanced defenses may be driven by fungal diversity at tropical latitudes, the most disease-resistant tropical males also showed the highest susceptibility to desiccation. This suggests potential trade-offs between abiotic stress resistance, necessary for survival in temperate habitats, and disease resistance. Furthermore, the study uncovered interactions between sex, mating status, sleep, and abiotic stresses, affecting disease resistance. Notably, longer-sleeping males and virgin flies survived infections longer, with additional daytime sleep post-infection being protective, particularly in the most resistant fly lines. These observations support the hypothesis that sleep and disease defense are intertwined traits linked to organismal fitness and subject to joint clinal evolution.