Ants are among the most successful organisms on Earth. It has been suggested that forming symbioses with nutrient-supplementing microbes may have contributed to their success, by allowing ants to invade otherwise inaccessible niches. However, it is unclear whether ants have evolved symbioses repeatedly to overcome the same nutrient limitations. Here, we address this question by comparing the independently evolved symbioses in Camponotus, Plagiolepis, Formica and Cardiocondyla ants. Our analysis reveals the only metabolic function consistently retained in all of the symbiont genomes is the capacity to synthesise tyrosine. We also show that in certain multi-queen lineages that have co-diversified with their symbiont for millions of years, only a fraction of queens carry the symbiont, suggesting ants differ in their colony-level reliance on symbiont-derived resources. Our results imply that symbioses can arise to solve common problems, but hosts may differ in their dependence on symbionts, highlighting the evolutionary forces influencing the persistence of long-term endosymbiotic mutualisms.

蚂蚁是地球上最成功的生物之一。有人认为，与补充营养的微生物形成共生关系可能有助于蚂蚁的成功，因为它们允许蚂蚁侵入其他难以进入的生态位。然而，目前尚不清楚蚂蚁是否通过反复进化共生来克服相同的营养限制。在这里，我们通过比较弓背蚁、斜鳞蚁、蚁蚁和心髁蚁独立进化的共生关系来解决这个问题。我们的分析表明，所有共生体基因组中一致保留的唯一代谢功能是合成酪氨酸的能力。我们还表明，在与共生体共同多样化了数百万年的某些多蚁后谱系中，只有一小部分蚁后携带共生体，这表明蚂蚁在群体层面对共生体衍生资源的依赖程度有所不同。我们的结果表明，共生体可以解决常见问题，但宿主对共生体的依赖可能有所不同，这凸显了影响长期内共生互利共生持续存在的进化力量。