Long-term selection for extended lifespan reshapes host physiology and gut microbiome structure in an insect model.

Longevity results from complex interactions between genetic, physiological, and environmental factors, however, the contribution of the gut microbiome to lifespan evolution is still poorly understood, especially in insects. In the present study, we tested whether long-term selection for delayed reproduction and extended lifespan can be associated with restructuring of the gut microbiome in the house cricket (Acheta domesticus). We compared a wild-type strain with a long-lived strain - selected for more than 20 years (64 generations) - maintained under the same laboratory conditions. The long-lived strain showed a significantly longer lifespan and larger body size. At the same time, no reduction in food intake or energy assimilation, no disturbance of antioxidant capacity, and no increased DNA damage were observed. These results support the supposition that lifespan extension was not primarily driven by metabolic suppression. Microbiome analyses showed strain-specific differences in community structure. Although overall microbial richness remained unchanged, the taxonomic analysis revealed two alternative microbial configurations: one characterized by higher relative abundance of Firmicutes and Bacteroidota in the wild-type strain and another enriched in Gammaproteobacteria and lactic acid bacteria in the long-lived strain. Our findings demonstrate that long-term selection can be associated with the emergence of strain-specific gut microbiome configurations. These differences may represent components of the longevity-associated phenotype, although their causal relationship with lifespan extension remains unresolved. Our results highlight the potential importance of gut microbiome variation during long-term life-history evolution in insects.