The origins of tropical marine biodiversity

► Recent phylogeographic studies overturn several assumptions about speciation in the sea, indicating a prominent role for divergence along ecological partitions rather than geographic isolation. ► Oceanic archipelagos and other depauperate regions are not evolutionary graveyards, but can generate and export biodiversity. ► Marine biodiversity hotspots both export and import fauna from peripheral areas in a synergistic process named biodiversity feedback. Recent phylogeographic studies have overturned three paradigms for the origins of marine biodiversity. (i) Physical (allopatric) isolation is not the sole avenue for marine speciation: many species diverge along ecological boundaries. (ii) Peripheral habitats such as oceanic archipelagos are not evolutionary graveyards: these regions can export biodiversity. (iii) Speciation in marine and terrestrial ecosystems follow similar processes but are not the same: opportunities for allopatric isolation are fewer in the oceans, leaving greater opportunity for speciation along ecological boundaries. Biodiversity hotspots such as the Caribbean Sea and the Indo-Pacific Coral Triangle produce and export species, but can also accumulate biodiversity produced in peripheral habitats. Both hotspots and peripheral ecosystems benefit from this exchange in a process dubbed biodiversity feedback.