Phylogenomics of an early-branching clade of Orthocladiinae (Diptera: Chironomidae)

The early-branching clade of Orthocladiinae and Prodiamesinae represent ancient, highly diverse, and ecologically adaptable key groups within Chironomidae (Diptera). Their larvae are widely distributed in freshwater ecosystems and serve as core bioindicators for water quality monitoring. However, due to historically incomplete geographical sampling and insufficient resolution of molecular markers, the taxonomic status of Prodiamesinae and the phylogenetic relationships among several problematic genera within the early-branching clade of Orthocladiinae have remained unresolved. This study systematically selected representative species from Prodiamesinae and the early-branching clade of Orthocladiinae to construct a highly confident molecular phylogenetic framework using universal single-copy orthologous nuclear genomic data. Key findings include: Prodiamesinae should be subsumed within Orthocladiinae, forming a sister group with Propsilocerus and treated as a synonym of Orthocladiinae (= Prodiamesinae syn. n.); the phylogenetic relationships among the early-branching clade of Orthocladiinae have been conclusively resolved; the origin of Orthocladiinae sensu lato (including Prodiamesinae and the early-branching clade of Orthocladiinae) dates back to the Early-Middle Jurassic (ca. 199–165 million years ago). These results reshape the higher-level classification system of Chironomidae, providing a reliable taxonomic foundation and evolutionary framework for future studies.