Dispersal sweepstakes: Biotic interchange propelled air-breathing fishes across the globe

Aim: Biotic interchanges between Africa, India, and Eurasia are central to explaining the present-day distribution and diversity of freshwater organisms across these landmasses. Synbranchiformes is a diverse and species-rich clade of freshwater acanthomorph fishes found on all southern continents except Antarctica, and include eel- and perch-like, air-breathing and non-air-breathing fishes. Lacking a comprehensive and resolved phylogeny of the entire clade, contemporary interpretations of synbranchiform biogeography invoke scenarios as disparate as Gondwanan vicariance and pan-global rafting to explain their modern-day distribution. Here, we study their biogeographic history of continental dispersal events and test whether these are associated with increases in lineage diversification.Location: Asia, India, Africa freshwater habitats.TaxonSynbranchiformes (gouramis, snakeheads, swamp eels, and relatives).Methods: We used nearly 1000 ultra-conserved elements (UCEs) and Sanger-sequenced genes to infer a phylogeny with representatives of all major synbranchiform lineages and nearly two-thirds of its known species diversity. Incorporating fossil calibrations, we inferred a time-calibrated phylogeny to which we apply Bayesian methods of ancestral area reconstruction and test for diversification rate shifts.Results: Analyses of UCE data provide a resolved phylogeny for major synbranchiform lineages. Divergence times support a most recent common ancestor of the entire clade approximately 79.2 million years ago. We infer significant increases in lineage diversification in both the spiny eels (Mastacembelidae) and the genus Betta (Osphronemidae).Main Conclusions: Our results reject the hypothesis of Gondwanan vicariance explaining synbranchiform biogeography. Instead, our analyses reconstruct a southeast Asian origin of the entire clade and independent dispersal events to other continents by snakeheads, anabantids, and spiny eels, with no signal of elevated lineage diversification occurring after these invasions. Higher lineage diversification rates in spiny eels pre-date their arrival to Africa, while the high diversification rates observed in Betta were initiated prior to the flooding of insular Sundaland in southeast Asia.