Extreme environments test the limits of life; yet, some organisms thrive in harsh conditions. Extremophile lineages inspire questions about how organisms can tolerate physiochemical stressors and whether the repeated colonization of extreme environments is facilitated by predictable and repeatable evolutionary innovations. We identified the mechanistic basis underlying convergent evolution of tolerance to hydrogen sulfide (H₂S)—a toxicant that impairs mitochondrial function—across evolutionarily independent lineages of a fish (Poecilia mexicana, Poeciliidae) from H₂S-rich springs. Using comparative biochemical and physiological analyses, we found that mitochondrial function is maintained in the presence of H₂S in sulfide spring P. mexicana but not ancestral lineages from nonsulfidic habitats due to convergent adaptations in the primary toxicity target and a major detoxification enzyme. Genome-wide local ancestry analyses indicated that convergent evolution of increased H₂S tolerance in different populations is likely caused by a combination of selection on standing genetic variation and de novo mutations. On a macroevolutionary scale, H₂S tolerance in 10 independent lineages of sulfide spring fishes across multiple genera of Poeciliidae is correlated with the convergent modification and expression changes in genes associated with H₂S toxicity and detoxification. Our results demonstrate that the modification of highly conserved physiological pathways associated with essential mitochondrial processes mediates tolerance to physiochemical stress. In addition, the same pathways, genes, and—in some instances—codons are implicated in H₂S adaptation in lineages that span 40 million years of evolution.

极端环境考验生命极限；然而，有些生物体在恶劣的条件下仍能茁壮成长。极端微生物谱系激发了人们对生物体如何耐受理化应激源以及极端环境的重复殖民是否是通过可预测和可重复的进化创新来促进的问题。_{我们确定了来自富含 H 2 S 泉水的鱼类（} Poecilia mexicana，Poeciliidae）进化独立谱系中对硫化氢（H ₂ S ）（一种损害线粒体功能的毒物）耐受性趋同进化的机制基础。通过比较生化和生理分析，我们发现硫化物泉墨西哥 P. mexicana中的线粒体功能在 H ₂ S存在下得以维持，但由于主要毒性目标和主要解毒酶的趋同适应，来自非硫化物栖息地的祖先谱系则不能维持线粒体功能。全基因组局部祖先分析表明，不同种群中 H ₂ S 耐受性增强的趋同进化可能是由长期遗传变异选择和从头突变相结合引起的。在宏观进化尺度上，Poeciliidae 多个属的 10 个独立的硫化物泉鱼谱系的 H _{2 S 耐受性与 H 2} S 毒性和解毒相关基因的趋同修饰和表达变化相关。我们的结果表明，与重要线粒体过程相关的高度保守的生理途径的修饰可介导对理化应激的耐受性。此外，在跨越 4000 万年进化的谱系中，相同的途径、基因和（在某些情况下）密码子与 H _{2 S 适应有关。}