Oxygen as a limiting ecological variable for invertebrate tissue maintenance
Ambient oxygen shapes tissue physiology, yet whether elevated oxygen directly perturbs stem cell fate and regeneration in invertebrates remains unclear. Here we test how chronic oxygen exposure influences intestinal stem cell (ISC) behaviour, epithelial homeostasis, and survival in Drosophila melanogaster, an organism lacking vertebrate-style stemness buffering via HIF-2a-driven pseudohypoxia. Adult flies were maintained under an atmosphere with moderate hypoxia (10% oxygen), normoxia (20% oxygen), and hyperoxia (40% oxygen) and assessed by lifespan analysis, midgut immunostaining, and intestinal transcriptomics. Hyperoxia markedly shortened lifespan, revealing high oxygen as a strong constraint on adult Drosophila viability. In the midgut, elevated O2 increased apoptosis and altered lineage outputs, with evidence of impaired fate segregation (mixed stem/differentiation marker expression) and a shift toward enteroendocrine differentiation. Consistent with these cellular phenotypes, transcriptomic profiling of the intestines at the onset of elevated mortality indicated enrichment of inflammatory signalling that compromised epithelial homeostasis. Together, our data support a model in which hyperoxia induces a 'non-productive regenerative state', where ISCs persist but their fate regulation and progeny survival are disrupted, leading to epithelial degeneration and reduced organismal viability. These findings position ambient oxygen as a key environmental variable that can destabilize stem cell-driven renewal in invertebrate tissues and motivate comparative studies on how oxygen-sensing strategies shape regenerative capacity across animal lineages. Overall design: RNAseq of dissected Drosophila melanogaster midgut growth under 10, 20, or 40% oxygen for 53 days.