Uncoupling ecological innovation and speciation in sea snakes (Elapidae, Hydrophiinae, Hydrophiini)

The viviparous sea snakes (Hydrophiini) are by far the most successful living marine reptiles, with ∼60 species that comprise a prominent component of shallow‐water marine ecosystems throughout the Indo‐West Pacific. Phylogenetically nested within the ∼100 species of terrestrial Australo‐Melanesian elapids (Hydrophiinae), molecular timescales suggest that the Hydrophiini are also very young, perhaps only ∼8–13 Myr old. Here, we use likelihood‐based analyses of combined phylogenetic and taxonomic data for Hydrophiinae to show that the initial invasion of marine habitats was not accompanied by elevated diversification rates. Rather, a dramatic three to six‐fold increase in diversification rates occurred at least 3–5 Myr after this transition, in a single nested clade: the Hydrophis group accounts for ∼80% of species richness in Hydrophiini and ∼35% of species richness in (terrestrial and marine) Hydrophiinae. Furthermore, other co‐distributed lineages of viviparous sea snakes (and marine Laticauda, Acrochordus and homalopsid snakes) are not especially species rich. Invasion of the oceans has not (by itself) accelerated diversification in Hydrophiini; novelties characterizing the Hydrophis group alone must have contributed to its evolutionary and ecological success.