Evolution and biogeography of the widespread dragonfly genus Orthetrum (Odonata: Anisoptera: Libellulidae): Massive dispersal in the tertiary

With 67 species, Orthetrum Newman is the most speciose genus within the family Libellulidae Leach (Odonata: Anisoptera), distributed across the Afrotropical, Palearctic, Indo-Malayan, Malagasy, Oceania, Wallacea and Australasian regions. Despite its wide distribution, serving as a top predator in freshwater ecosystems, the evolutionary history of Orthetrum has remained unresolved, with prior studies limited to morphology and sparse genetic sampling (<33% of species). We present here the most comprehensive phylogenetic study of Orthetrum to date, sampling 50 of 67 species (~75%) using Anchored Hybrid Enrichment (AHE). Our analyses, integrating concatenated maximum likelihood and coalescent-based approaches, provide a robust, strongly supported phylogeny that confirms the monophyly of Orthetrum and reveals four distinct clades. Two clades comprise mostly Afrotropical species, whereas the remaining clades are from the Palearctic, Indo-Malayan, Oceania, Wallacea and Australasian regions. Divergence time estimates indicate that Orthetrum originated ~32 million years ago, with major diversification occurring from ~28 Ma onward, well after major continental fragmentation events. Ancestral range reconstruction under the best supported Dispersal–Extinction–Cladogenesis (DEC) framework does not support a single-region origin; instead, early lineages are inferred to have occupied a broadly connected Afro–Eurasian system. Subsequent diversification is characterized by stepwise dispersal across adjacent regions, including repeated expansions into the Indo-Malayan and Palearctic regions, followed by colonization of Australasia, Wallacea and Oceania. The Afrotropical region emerges as a major centre of lineage persistence and diversification, with subsequent range expansion in some lineages during the early Miocene (~23 Ma), whereas Madagascar reflects at least five independent colonization events from Africa resulting in endemic species.