Phylogenomic reconstruction illuminates the evolutionary history of freshwater to marine transition in the subfamily Haloveliinae (Hemiptera: Heteroptera: Veliidae)

Water crickets of the subfamily Haloveliinae are semi-aquatic bugs occurring in freshwater and marine habitats throughout the Indo-Australian region, presently including six genera with more than 80 extant species. Whether lineage diversification in Haloveliinae is associated with the utilization of new ecological niches caused by transition events between freshwater and marine habitats remains poorly understood. We investigate the evolutionary history of Haloveliinae using large-scale phylogenomic datasets and a set of novel redefined morphological characters based on 24 ingroup taxa representing all recognized genera. Our phylogenetic results based on the novel datasets definitively indicate that the freshwater genus Strongylovelia Esaki as currently defined is paraphyletic and supports the establishment of a new genus: Metavelia gen. nov., including three congeneric species: Metavelia patiooni comb. nov. (type species), Metavelia priori comb. nov. and Metavelia albicolli comb. nov. Reconstruction of ancestral habitats suggests a freshwater origin for the Haloveliinae. Divergence time estimations reveal that the origin of the monophyletic marine clade occurred at around 83 Ma (95% highest posterior density: 71–98 Ma) in the Late Cretaceous, involving a single transition event from freshwater to marine habitats. This time coincides with the period of high global sea levels in the Late Cretaceous. During this period, the marine incursions caused by the massive sea level rise flooded the continental margins, especially in Southeast Asia, where ancestral Haloveliinae were probably distributed. The appearance of new marine habitats after the marine incursions (e.g., intertidal, mangroves and estuarine) probably led to a subsequent establishment and diversification of the marine lineages.