The evolution of marine insects: phylogenetic, ecological and geographical aspects of species diversity in marine water striders

No other group of insects have been more successful in colonizing marine habitats than water striders and their allies (Heteroptera, Gerromorpha). More than 10% of the 1700 species of gerromorphan bugs are marine. Water striders have colonized the marine environment at least 14 times. The fossil records suggest that marine habitats were invaded by members of the families Veliidae and Gerridae earlier than 20‐30 and 45 million years before present, respectively. Estuaries and mangrove swamps are undoubtedly the ancestral type of habitat, but water striders have diversified further in marine habitats including the surface of the open ocean (sea skaters. Halobates). Except for being obligatorily flightless, marine water striders are structurally very similar to their non‐marine relatives. Physiological and behavioral rather than morphological specializations are likely to have been key innovations in the transition from limnic to marine habitats. The oldest and most species‐rich clades originated in the Indo‐West Pacific region. There are 3.5 times as many species of marine water striders in the Indo‐West Pacific region than in the Atlantic/Caribbean/East Pacific region. This “diversity anomaly” is explained historically by region‐specific differences in the origin and proliferation of clades, in paleoclimate and paleogeography, and in the propensity for dispersal between regions.