Marine water striders of the Indo-Pacific 341 Marine water striders (Heteroptera, Gerromorpha) of the Indo-Pacific: cladistic biogeography and Cenozoic palaeogeography N Møller Andersen Zoological Museum, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark Email: nmandersen@zmuc*ku*dk Key words: cladistic biogeography, Cenozoic palaeogeography, Indo-Pacific, marine water striders, Heteroptera, Gerromorpha Abstract Boer and Duffels, 1996) In general, patterns of distribution seem to be compatible with a set of More than 140 species of marine water striders (Heterop- hierarchical relationships between more re- tera, Gerromorpha), representing three families and 11 gen- stricted areas of endemism These are quite simi- era, are distributed throughout the Indo-Pacific region! The lar to those delimited by Gressitt (1956) and largest genera are: Hermatobates (Hermatobatidae), Halove- lia, Haloveloides, Xenobates (Veliidae), Asclepios, Halobates, Gressitt et al* (1961), although the areas of the Rheumatometroides, and Stenobates (Gerridae)! Marine wa- Indian Ocean were not recognized as part of ter striders live in estuaries, mangroves, intertidal coral reef their Pacific region Malesia (as defined by flats, and on the sea surface near coral reefs and rocky Whitmore, 1981, 1987) is seemingly not a genu- coasts! Adult marine water striders are always wingless but may disperse along coasts and chains of islands! Five spe- ine, monophyletic area of endemism (Andersen, cies of sea skaters, Halobates, have colonized the surface of 1991a) the open ocean! The present work updates and extends pre- Most studies of Indo-Pacific biogeography vious work on the cladistic biogeography of Indo-Pacific have been based upon terrestrial animals and marine water striders! The method of paralogy-free subtree plants In this chapter, the results of biogeo- analysis developed by Nelson and Ladiges is applied to tax- on-area cladograms for four monophyletic groups, and the graphical studies of a group of marine insects results are combined to yield general area cladograms de- belonging to the heteropterous infraorder picting the relationships between eight areas of endemism Gerromorpha are presented Although the ma- of the Indo-Pacific region! Finally, hypotheses of area rela- jority of the about 1,600 gerromorphan species tionships are discussed in the light of available knowledge are limnic, about 180 species belonging to five about the distribution of fossil marine water striders, the Cenozoic palaeogeography of the Indo-Pacific region, and families and seven subfamilies occur in the ma- the palaeoecology of mangroves and reef-building corals! rine environment and reach their greatest diver- sity in the Indo-Pacific region (Andersen and Polhemus, 1976; Andersen, 1982; Cheng, 1985) Introduction The present work updates and extends previous works on the cladistic biogeography of Indo- The Indo-Pacific comprises land areas bordering Pacific marine water striders (Andersen, 1991a, the Indian and west Pacific Oceans (Fig1) and 1991b; Andersen and Weir, 1994a, 1994b) The has traditionally been divided into the Ethio- method of paralogy-free subtree analyses (Nel- pian, Oriental, and Australian regions Studies son and Ladiges, 1996) is applied to taxon-area using the methods of cladistic biogeography cladograms for four monophyletic groups of (Nelson and Platnick, 1981; Humphries and marine water striders and the results are com- Parenti, 1986; Humphries et al*, 1988), however, bined to yield general area cladograms depict- do not support this division (e*g*, Schuh and ing the relationships between areas of ende- Stonedahl, 1986; Andersen, 1991a; Muona, 1991; mism of the Indo-Pacific region Finally, the hy- Parenti, 1991; Vane-Wright, 1991; Boer, 1995; potheses of area interrelationships are discussed Biogeography and Geological Evolution of SE Asia, pp 341-354 Edited by Robert Hall and Jeremy D Holloway © 1998 Backhuys Publishers, Leiden, The Netherlands 342 N* Møller Andersen Fig 1 The Indo-Pacific with distribution of nearshore species of marine water striders (hatched areas) and distributional boundaries of oceanic Halobates (dashed line)! Insertions show Halovelia malaya Esaki, length 2!5 mm (bottom left) and Halobates sericeus Eschscholtz, length 3!4 mm (top right)! in the light of available knowledge about the marine water striders have rather restricted areas Cenozoic palaeogeography of the region (Boer, of distribution 1995; Boer and Duffels, 1996; Packham, 1996; Hall, 1996, and references therein) Hermatobates Marine water striders and their distribution The genus Hermatobates contains eight de- scribed species, but a taxonomic revision is re- General quired The biology of these odd marine insects was studied by Foster (1989), who named them More than 140 species of marine water striders, coral treaders because they live on the tidal flats representing three families and 11 genera, are of coral reefs Both adults and nymphs retreat to distributed throughout the Indo-Pacific region holes in porous blocks of dead coral during They live in estuaries, mangroves, intertidal high tides Hermatobates is unique (Andersen, coral reef flats, and on the sea surface near coral 1982), belonging to its own family, one of few reefs and rocky coasts (Fig1) Five species of exclusively marine insect families It has no sea skaters, Halobates, have colonized the sur- close freshwater relatives and it is difficult to face of the open ocean (Cheng, 1985, 1989) trace its geographical origin Hermatobates spe- Adult marine water striders are always wingless cies are found along continental coasts and is- but may disperse along coasts, chains of islands lands throughout the Indo-Pacific Widespread and, for a few species of Halobates, possibly species are H* djiboutensis Coutière and Martin across wider stretches of open sea Although (Red Sea, East Africa, Seychelles, Maldives), H* some species belonging to the genera Halovelia marchei Coutière and Martin (Ryukyu Islands, and Halobates are widespread, most species of Philippines, Indonesia, Australia, islands of the Marine water striders of the Indo-Pacific 343 West Pacific), and H* hawaiiensis China (Hawai- placed in Halovelia (China, 1957; Polhemus, ian Islands and islands of Central Pacific) H* 1982; Lansbury, 1989) A preliminary class- breddini Herring (Caribbean) is the only species ification of Xenobates species has revealed a found outside the Indo-Pacific region number of monophyletic species groups (Andersen, unpublished) The X* seminulum (Esaki) group (with four species) occurs in Halovelia Maluku, northern New Guinea, the Bismarck archipelago and Solomon Islands A related The subfamily Haloveliinae belongs to the species group is found in Maluku, Sulawesi, Veliidae, one of the most speciose families of southern Philippines, Java, Singapore, and Sri water striders, with more than 600 species Most Lanka Another group occurs in Maluku, haloveliines are marine Freshwater relatives be- Sulawesi, southern Philippines, North Borneo, long to two genera: Entomovelia with one de- and Malaya Eight species of Xenobates, most of scribed and some undescribed species in them undescribed, are found along the coast of Burma, Malaya and Borneo, and Strongylovelia tropical Australia (Andersen and Weir, with several, mostly undescribed, species in the unpublished) Finally, X* loyaltiensis (China) is Indo-Australian region The marine Haloveliinae endemic to New Caledonia and the Loyalty have been classified into three genera, Halo- Islands velia, Xenobates, and Haloveloides (Andersen, A separate genus, Haloveloides, with seven 1989a, 1989b, 1992; Lansbury, 1989, 1996) So species, was erected for the Halovelia far, 45 species have been described, but during papuensis Esaki group (Andersen, 1992) It is the past 10 years, marine haloveliines have been closely related to Xenobates but some species collected in many new localities, increasing the have left the protecting mangroves and live on number of known species to more than 60 the sea surface at some distance from the coast Species of Halovelia or coral bugs inhabit the (Lansbury, 1996) One species is found in areas intertidal zone of rocky coasts or coral reefs of the Sunda shelf, another one in Sulawesi, where they can be found on the surface of tidal Maluku, and southern Philippines, three species pools At high tide they retreat to holes in blocks in Palawan and Luzon, and another two species of coral or other porous rocks where they rest, in northern New Guinea, the Bismarck archi- surrounded by an air bubble, until the next low pelago and the Solomons tide (Andersen, 1989b) The 32 described spe- cies of the genus Halovelia range from the Red Sea and East African coast to the West Pacific Stenobates and Rheumatometroides islands as far as Samoa (Andersen, 1989a, 1989b) Species belonging to the H* esakii group Another large family of water striders, the occur along the coasts of the Philippines, Gerridae, with more than 500 species, contains Sulawesi, New Guinea, the Solomons, northern several groups of marine species The tribe Australia, and the Fiji and Tonga Islands Species Stenobatini has 21 mangrove-inhabiting species of the H* bergrothi group have a similar distribu- in Malesia (Polhemus and Polhemus, 1996) tion but two species are widespread in Australia They belong to the subfamily Trepobatinae and and the islands of the West Pacific, respectively are related to the freshwater genus Naboandelus Two closely related species, the H* lannae found