Global diversity of water mites (Acari,Hydrachnidia; Arachnida) in freshwater

The Hydrachnidia (water mites) represent the most important group of the Arachnida in fresh water. Over 6,000 species have been described worldwide, representing 57 families, 81 subfamilies and more than 400 genera. The article analyzes extant water mite diversity and biogeography. Data on distribution and species richness of water mites are substantial but still far from complete. Many parts of the world are poorly investigated, Oriental and Afrotropical regions in particular. Moreover, information among different freshwater habitats is unbalanced with springs and interstitial waters disproportionately unrepresented. Therefore, more than 10,000 species could be reasonably expected to occur in inland waters worldwide. Based on available information, the Palaearctic region represents one of the better investigated areas with the highest number of species recorded (1,642 species). More than 1,000 species have been recorded in each of the Neotropical (1,305 species) and Nearctic regions (1,025 species). Known species richness is lower in Afrotropical (787 species) and Australasian (694 species) regions, and lowest in the Oriental region (554 species). The total number of genera is not correlated with species richness and is distinctly higher in the Neotropical (164 genera); genus richness is similar in the Palaearctic, Nearctic and Australasian regions (128–131 genera) and is lower in the Afrotropical and Oriental regions with 110 and 94 genera, respectively. A mean number of about three genera per family occur in the Palaeartic, Nearctic and Oriental while an average of more than four genera characterizes the families of Australasian and Afrotropical regions and more than five genera those of the Neotropical. Australasian fauna is also characterized by the highest percentage of endemic genera (62%), followed by Neotropical (50.6%) and Afrotropical (47.2%) regions. Lower values are recorded for the Palaearctic (26.9%), Oriental (24.4%) and Nearctic (21.4%). The Palaearctic and Nearctic have the highest faunistic similarity, some minor affinities are also evident for the generic diversification of Holarctic and Oriental families. The faunas of Southern Hemisphere bioregions are more distinct and characterized by the presence of ancient Gondwanan clades with a regional diversification particularly evident in the Neotropics and Australasia. This scenario of water mite diversity and distribution reflect the basic vicariance pattern, isolation, phylogenetic diversification, recent climatic vicissitudes and episodes of dispersal between adjacent land masses together with extant ecological factors can be evoked to explain distribution patterns at a global scale. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

Allocation of reproductive effort in female Arrenurus spp. water mites (Acari: Hydrachnidia; Arrenuridae)

Summary Twenty-seven species of water mites of the genus Arrenurus were compared with respect to allocation of reproductive effort. Clutch volume was positively correlated to female volume, female volume was positively correlated with clutch size and with larval volume, while clutch size and larval volume were negatively correlated. In threespace, corresponding to female volume, clutch size and larval volume, species were arranged along two trajectories representing separate reproductive strategies. The strategy characterized by small larvae, large clutches and large females corresponded to species of the subgenus Arrenurus, known to be larval parasites of adult Odonata. Members of three subgenera, known to be larval parasites of adult Diptera, followed the second strategy of small clutch size and alrge larvae. Of nine species of mites tested for intraspecific relationships, only one significant relationship was found, between female volume and clutch size for A. (Megaluracarus) bartonensis.     

Biodiversity and distribution of water mites (Acari, Hydrachnidia) in spring habitats

1. The distribution, species richness and ecology of spring‐dwelling water mites in Italy were investigated with the aim to better elucidate the role of spring habitats to sustain high levels of biodiversity and their contribution to freshwater biodiversity at a local and regional scale. 2. More than 300 springs in different geographic areas (Alps, Central and Southern Apennines, Sicily and Sardinia), were examined with a total of 163 water mite species recorded. 3. Species richness in each area ranged from 33 species on Sardinia to 77 on Sicily. The highest diversity was found in the Gran Sasso (Central Apennines). The proportion of crenobionts (species strictly bound to this type of habitat) exceeded 50% in almost all the areas investigated. 4. A diverse (up to 20 species per spring) and highly specialised mite fauna was observed in undisturbed rheocrenes and in natural springs of intermediate typology (rheohelocrenes and rheopsammocrenes). In springs subjected to human impacts (pasture, deforestation, alteration and transformation of spring sources) species richness declined and crenobionts were replaced by unspecialised crenoxenes. 5. The zoogeographic importance of spring habitats is confirmed by the presence of 18 endemic species and by members of genera with an interesting disjunct and relict distribution. 6. A comparison with other geographic areas suggests that springs contain a significant fraction of the total number of species found in freshwater habitats and may contribute almost one third of regional freshwater biodiversity. The presence of endemic crenobionts and rare taxa highlights the importance of these habitats in maintaining high levels of biodiversity as well as their contribution to a better understanding of biodiversity patterns in freshwaters.     

Parasite-host associations and life cycles of spring-living water mites (Hydrachnidia, Acari) from Luxembourg

Larval water mites are parasites of various insect species. The main aim of the present study was to analyse the host range of spring dwelling water mites. The investigation focuses on seven spring sites in Luxembourg. Some 24 water mite species were recorded either from the benthos or as parasites attached to flying insects captured in emergence traps. For 20 mite species 35 host species from four Nematocera (Diptera) families were recorded. About 80% of the host species and over 90% of the host individuals were Chironomidae, the others were Limoniidae, Dixidae and Simuliidae. For all water mite species recorded we present the observed host spectrum and/or potential hosts as well as the intensity of parasitism and the phenology of the mites. For 10 mite species the hosts were previously unknown. For another ten species the known host spectrum can be confirmed and extended. The host spectrum ranged from one host species (e.g. for Sperchon insignis) to at least 10 host species (for Sperchon thienemanni, Ljania bipapillata), but the effective host range could not be definitively estimated due to the lack of corresponding data. The hypothesised host preference of the water mites, of which most are strictly confined to spring habitats, for similarly spring-preferring hosts could not be proven. The mean intensity of parasitism was highest for Thyas palustris (10.8 larvae/host) and lowest for Sperchon insignis and Hygrobates norvegicus (1.2 larvae per host for each). The hydryphantid mite Thyas palustris occurred at maximal intensity (41 larvae per host) and the two abdominal parasites Ljania bipapillata and Arrenurus fontinalis showed higher mean intensities than the thoracic parasites did. Larval water mites parasitising chironomids did not exhibit a preference for host sex. The phenology of the larval mite species was varied, some species were only present in samples early in the year and others exclusively in the summer. Another species showed two peaks of occurrence, springtime/early summer and late summer/autumn. In conclusion, the water mite larvae in the studied springs showed differences in host spectra and phenology but there are no clear evidences in both for host partitioning. Maybe, the relative low species diversity of water mites in individual springs and the low inter-specific competition for suitable hosts in combination with the high host abundances and species richness makes springs such favourable habitats for the mites.     

Descriptions of Atractides aprojectus sp.nov.and male of A.huaxiensis Yi & Jin (Acari: Hydrachnidia) from China

A water mite species is described as new to science, Atractides(Tympanomegapus) aprojectus sp. nov. The male of Atractides(Tympanomegapus) huaxiensis Yi & Jin, 2010 is described for the first time from Guizhou Province, China. The materials were collected during a survey in 2011 from the rivers in Guizhou. The specimens are deposited in the Institute of Entomology, Guizhou University(GUGC).     

Larval parasitism of spring-dwelling alpine water mites (Hydrachnidia,Acari): a study with particular reference to chironomid hosts

During faunistic investigations on spring habitats in the alpine National Park Berchtesgaden (Bavaria, Germany), water mites were found to be the group with the highest share of species strongly adapted to springs. At four sample sites at two spring complexes, insect emergence was screened for parasitism by larval water mites. A total of at least 36 host species were recorded as being parasitized by 19 water mite species. As in many other habitats, the most important host taxon was shown to be the nematoceran family Chironomidae, both in the number of species and individuals parasitized. Likewise, the number of water mite species attached to chironomids was high. Further host species were found among the Plecoptera, Trichoptera, Coleoptera, Limoniidae and Empididae (Diptera). These taxa were only parasitized by a single water mite species in each case. For 13 mite species, new hosts were recorded for the first time. For another six species, the known host spectrum could be confirmed and/or supplemented. The parasitological data presented (e.g., prevalences, selected attachment sites on the host, larval phenology, intensity of parasitism) provide, in most cases, basic information concerning previously unknown parasite–host associations. At this time, the reason for the strong crenobiosis in water mites cannot be explained by their parasitism.     

A new genus of water mites (Acari,Hydrachnidia, Wettinidae) from bromeliad phytotelmata in the Brazilian Atlantic rainforest

Adults of Bromeliacaruscardosogen. n., sp. n. are described from phytotelmata of Quesneliaarvensis (Vellozo) Mez. (Bromeliaceae) in the subtropical area of the Atlantic rainforest, São Paulo State, Brazil. The new genus Bromeliacarus is proposed and diagnosed, based primarily on the autapomorphic presence of 7–9 pairs of acetabula flanking the gonopore. A possible relationship between Bromeliacarus and other Wettinidae are discussed.     

Further studies on water mites from Korea,with description of two new species (Acari,Hydrachnidia)

New records of water mites (Acari: Hydrachnidia) from streams in South Korea are presented. Two species are described as new to science: Torrenticola neodentifera sp. n. (Torrenticolidae) and Atractides ermilovi sp. n. (Hygrobatidae). Five species are reported as first records for Korea: Wandesia (Wandesia) reducta Tuzovskij, 1987, Wandesia (Wandesia) cf. rara Tuzovskij, 1990, Sperchon (Sperchon) orientalis Tuzovskij, 1990, Feltria (Feltria) kuluensis Tuzovskij, 1988 and Atractides (Atractides) constrictus (Sokolow, 1934). The latter species is redescribed and elevated to species rank based on new material from the Russian Far East.     

The water mites (Acari: Hydrachnidia) of streams in The Netherlands: Distribution and ecological aspects on a regional scale

The water mites of running waters in The Netherlands have been surveyed for the period 1987–1992. The aims were to investigate their present distribution, to make a comparison with historical data and to identify differences in water mite assemblages on a regional scale. The investigation covered 821 sites in eight different drainage areas. In spite of the scarcity of historical data, it may be concluded that in the course of this century about 40% of rheophilic water mites have become extinct. In canalized streams lentic species are dominant. In springs and spring streams, lotic species can survive, but the assemblages consist mainly of euryoecious water mite species.Multivariate techniques were used to show regional differences. These differences are mainly determined by stream hydraulics. The area of Zuid-Limburg can easily be demarcated by its relatively high number of rheophilic species. The man-made streams (sprengen) at the east side of the Veluwe area are characterized by a number of species which indicate undisturbed circumstances. The response of water mites to pollution of running waters is discussed.     

Attachment site and infestation parameters of parasitic water mites on the whirligig beetle Dineutus nigrior Roberts (Coleoptera: Gyrinidae)

Larval water mites parasitise a wide range of aquatic insects and may have a negative impact on host fitness. One host taxon susceptible to water mite parasitism is the whirligig beetle (Coleoptera: Gyrinidae). We made 11 collections of the whirligig beetle Dineutus nigrior Roberts from May to October of 2006 to investigate patterns of water mite parasitism on that host species. Mites were identified as of the genus Eylais. Mite intensity ranged from 1 to 11. Median intensity was 1.0 and ranged from 1.0 to 3.0 for individual samples. There did not appear to be temporal patterns in mite intensity. Prevalence was 30.9% but varied substantially over the sampling period ranging from 2.5 to 63.3%. Mites were attached to the metathoracic wings and the body tergites under the elytra. When all samples were considered there was equal use of wings and body tergites but there was temporal variation in the use of attachment sites.     

Diversity, distribution and ecology of water mites (Acari: Hydrachnidia and Halacaridae) in high Alpine lakes (Central Alps, Italy)

Information on water mite assemblages from high elevation lentic biotopes is scant. A survey of 14 small Alpine lakes located between1900 and 2400 m a.s.l. in Italy resulted in the discovery of 17 species of Hydrachnidia and a single species of freshwater Halacaridae. Arrenurus conicus and Lebertia tuberosa were the most widespread and abundant species; Lebertia sefvei, Lebertia rufipes, Oxus setosus, Panisus torrenticolus and Sperchon glandulosus were also widely distributed but relatively less abundant. Atractides fissus and Arrenurus conicus are recorded for the first time from Italy. In contrast to mid/low elevation lakes and ponds, water mite assemblages of alpine lakes are less diverse and are composed mainly of rheo- and crenobiontic taxa, most of which are cold-stenothermic. Typical standing water dwellers represented only a small fraction (23%) of the species sampled. A principal component analysis conducted on lake environmental variables resulted in a clear separation of the lakes mainly based on ionic contents, pH and temperature. Water mites seem to be less influenced by these factors than by temperature fluctuations and habitat stability and heterogeneity. We conclude with some considerations of the influence of abiotic and biotic factors on the altitudinal and latitudinal distribution pattern of water mites.     

Diversity, distribution and ecology of water mites (Acari: Hydrachnidia and Halacaridae) in high Alpine lakes (Central Alps, Italy)

Information on water mite assemblages from high elevation lentic biotopes is scant. A survey of 14 small Alpine lakes located between 1900 and 2400 m a.s.l. in Italy resulted in the discovery of 17 species of Hydrachnidia and a single species of freshwater Halacaridae. Arrenurus conicus and Lebertia tuberosa were the most widespread and abundant species; Lebertia sefvei, Lebertia rufipes, Oxus setosus, Panisus torrenticolus and Sperchon glandulosus were also widely distributed but relatively less abundant. Atractides fissus and Arrenurus conicus are recorded for the first time from Italy. In contrast to mid/low elevation lakes and ponds, water mite assemblages of alpine lakes are less diverse and are composed mainly of rheo- and crenobiontic taxa, most of which are cold-stenothermic. Typical standing water dwellers represented only a small fraction (23%) of the species sampled. A principal component analysis conducted on lake environmental variables resulted in a clear separation of the lakes mainly based on ionic contents, pH and temperature. Water mites seem to be less influenced by these factors than by temperature fluctuations and habitat stability and heterogeneity. We conclude with some considerations of the influence of abiotic and biotic factors on the altitudinal and latitudinal distribution pattern of water mites.     

Mating and spermatophore morphology of water mites (Acari: Parasitengona)

In this paper I synthesize original and published studies of sperm transfer behaviour of 23 genera of water mites from 15 families. The morphology of spermatophores from 16 genera (12 families) is described. Behaviour and/or spermatophores are described for the first time for the following species: Hydrachna magniscutata Marshall, Hydrachna hesperia Lundblad, Hydrachna sp. nr. leegei Koenike, Limnochares americana Lundblad, Limnesia undulata (Müller), Neumania distincta Marshall, Unionicola (three species in the U. crassipes-complex), Thyas slolli Koenike, Lebertia annae Habeeb, Lebertia sp., Piona sp. nr. debilis (Wolcott), Tiphys vernalis (Habeeb), Arrenurus dentipetiolatus Marshall, Arrenurus marshalli Piersig and Arrenurus birgei Marshall. On the basis of proximity of male and female during sperm transfer, I divide water mites into four groups: complete dissociation, involving no physical or chemical contact between the sexes (nine genera); incomplete dissociation, requiring distance-or contact-chemoreception but not involving pairing behaviour (five genera); pairing with indirect transfer, involving pairing behaviour with females controlling sperm uptake (three genera); pairing with direct transfer (=copulation), involving pairing behaviour and male placement of sperm in the receiving structure of the female (12 genera). Four genera have representative species in more than one category of sperm transfer. Factors possibly leading to the diversity of water mite mating behaviour include an evolutionarily flexible mode of sperm transfer in the ancestral water mite, and the development of planktonic and endoparasitic habits in many mites. Morphological features of spermatophores that improve physical stability, probability of females taking up sperm and resistance against osmotic stress are discussed. Finally, I present implications of mating behaviour and spermatophore morphology for phylogenetic relationships within water mites and between this group and terrestrial Acari.     

Seasonal variation in the diel vertical distribution of the migratory alga Cryptomonas marssonii (Cryptophyceae) in a small,highly humic lake

The diel vertical distribution patterns of a migratory alga Cryptomonas marssonii in a small, steeply stratified humic lake were investigated during a summer season (10 diurnal experiments between May and September) using a close-interval Blakar-type sampler. The results indicate that the cells were phototactic; they were typically concentrated at the surface or subsurface during daylight, while in darkness the highest densities were recorded in deeper water, usually near the upper limit of anoxia. During a dense blue-green bloom in August the cells of C. marssonii were also concentrated by day into the same water layer, where oxygen was depleted. However, the cells seemed to avoid totally anoxic water. Because the vertical distribution pattern of C. marssonii had special diurnal and seasonal characteristics, care is needed when designing a sampling programme for a phytoplankton population dominated by this species.     

Isolation and characterization of polymorphic microsatellite loci from the water mite Hygrobates fluviatilis (Acari: Hydrachnidia: Hygrobatidae)

We developed and characterized 13 microsatellite markers from the water mite Hygrobates fluviatilis. The genotypes of 32 diploid females were assessed, and all of the loci were polymorphic. The number of alleles per locus ranged from two to 21, and the observed heterozygosity ranged from 0.063 to 0.813. These microsatellite markers are the first published for water mites and will contribute to research on the population structure of this widespread species.     

Two new species of the marine water mite family Pontarachnidae from Queensland,Australia (Acari: Hydrachnidia)

Two new species of the water mite family Pontarachnidae are described from Queensland, Australia: Pontarachna curvipalpis and Litarachna haleioides. Pontarachna curvipalpis can be distinguished from other members of the genus by its stocky leg segments, long apodemes of the fourth coxae, strongly bowed pre- and postgenital sclerite and wheel-like acetabula without radiating spokes. Litarachna haleoides is characterized by strongly bowed but not touching genital sclerites, relatively short apodemes of the fourth coxae, a slender palp and P2 with a ventral projection. A short discussion is provided on the occurrence of water mites on the Great Barrier Reef.