A standardised framework for classifying estimates of reproductive isolation across the Tree of Life

Understanding reproductive isolation (RI) between lineages is a central goal of speciation research. While the strength of RI has been estimated across a broad range of taxa, synthesising these data remains challenging, partially because we lack a common language for classifying and reporting RI estimates. Here, we present the Reproductive Isolation Ontology (RIO), a structured framework designed to standardise the classification of RI estimates across the Tree of Life. The RIO comprises three interrelated domains, each organised into a nested hierarchy of classification terms. We demonstrate the utility of this approach and call for researchers to adopt the RIO to facilitate the integration of speciation research.