Coupling of diversification and pH adaptation during the evolution of terrestrial Thaumarchaeota

The link between species diversification and adaptation has long interested biologists working on multicellular eukaryotes, but remains poorly understood in prokaryotes, in which diversity is much greater. We tested the hypothesis that diversification is associated with environmental adaptation in Thaumarchaeota, an ancient and abundant microbial group and key player in the global nitrogen cycle. We provide evidence that the Thaumarchaeota underwent a major radiation event hundreds of millions of years ago that coincided with a major period of pH adaptation. Subsequently, these microbes have maintained high rates of diversification, potentially because of the high rate at which new terrestrial niches arise. This study provides a framework for comparing dynamics of evolutionary processes across the tree of life.