Global diversity of black flies (Diptera: Simuliidae) in freshwater

Black flies are a worldwide family of nematocerous Diptera whose immature stages are confined to running waters. They are key organisms in both aquatic and terrestrial ecosystems, but are perhaps best known for the bloodsucking habits of adult females. Attacks by black flies are responsible for reduced tourism, deaths in wild and domestic birds and mammals, and transmission of parasitic diseases to hosts, including humans. About 2,000 nominal species are currently recognized; however, certain geographical regions remain inadequately surveyed. Furthermore, studies of the giant polytene chromosomes of larvae reveal that many morphologically recognized species actually consist of two or more structurally indistinguishable (yet reproductively isolated) sibling species. Calculations derived from the best-known regional fauna—the Nearctic Region—reveal that the actual number of World black fly species exceeds 3,000. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: E.V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

Global diversity of Isopod crustaceans (Crustacea; Isopoda) in freshwater

The isopod crustaceans are diverse both morphologically and in described species numbers. Nearly 950 described species (∼9% of all isopods) live in continental waters, and possibly 1,400 species remain undescribed. The high frequency of cryptic species suggests that these figures are underestimates. Several major freshwater taxa have ancient biogeographic patterns dating from the division of the continents into Laurasia (Asellidae, Stenasellidae) and Gondwana (Phreatoicidea, Protojaniridae and Heterias). The suborder Asellota has the most described freshwater species, mostly in the families Asellidae and Stenasellidae. The suborder Phreatoicidea has the largest number of endemic genera. Other primary freshwater taxa have small numbers of described species, although more species are being discovered, especially in the southern hemisphere. The Oniscidea, although primarily terrestrial, has a small number of freshwater species. A diverse group of more derived isopods, the ‘Flabellifera’ sensu lato has regionally important species richness, such as in the Amazon River. These taxa are transitional between marine and freshwater realms and represent multiple colonisations of continental habitats. Most species of freshwater isopods species and many genera are narrow range endemics. This endemism ensures that human demand for fresh water will place these isopods at an increasing risk of extinction, as has already happened in a few documented cases. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

Differences in dispersal- and colonization-related traits between taxa from the freshwater and the terrestrial realm

The aquatic and terrestrial realms differ in many physical properties that not only require specific physiological adaptations but also cause differences in dispersal options. We thus expect that life-history traits related to dispersal and colonization are under selection pressure because freshwater habitats are more isolated and thus more difficult to reach. We compared traits from European databases of three taxonomic groups along the passive–active dispersal gradient: plants (Plantes), snails (Mollusca: Gastropoda: Prosobranchia et Pulmonata) and hoverflies (Diptera: Syrphidae), all of which have both terrestrial and freshwater species (plants and snails) or early life stages (hoverflies). Aquatic taxa seem to be more successful long-distance dispersers than are terrestrial taxa. Our analysis also revealed lower numbers of seeds or eggs produced in the aquatic habitats. However, aquatic taxa often allocate resources to offspring guarding (vegetative propagules in plants, egg capsules in snails) and breeding-site selection (syrphids). Colonization of the aquatic realm is reinforced by increases in life span (plants), clonal spread (plants), shorter generation times (snails), selfing ability (marginal effect in pulmonate snails) or paedogenesis (two incidences in hoverflies, needs further studies). Probably, the variety of strategies reflects the different evolutionary backgrounds that elicit different combinations of trade-offs, but all traits also might increase invasibility of species.     

The morphology of the larval head of Tipulidae (Diptera, Insecta) - The dipteran groundplan and evolutionary trends

External and internal head structures of the larva of Tipula montium are described in detail. The results are compared to conditions found in other representatives of Tipuloidea and other dipteran and antliophoran lineages. Despite of the conceivably basal position of Tipulomorpha within Diptera, the larvae are mainly characterised by derived features. The partially retracted head, the specific hemicephalic condition and several other derived character states support the monophyly of Tipuloidea. A clade comprising Tipuloidea excluding Pediciidae is suggested by the strongly retracted head, by deep dorsolateral incisions of the head capsule, by a distinctly toothed anterior premental margin, by the loss of the second extrinsic maxillary muscle, and possibly by the loss of the pharyngeal filter. Eriopterinae and Hexatominae are characterised by a tendency towards an extreme reduction of the head capsule. Limoniinae, Cylindrotomidae, and Tipulidae form a clade supported by the presence of a premaxillary suture. This implies the non-monophyly of Limoniidae. A feature shared by Cylindrotomidae and Tipulidae is the presence of a movable lacinia mobilis. However, this is arguably a plesiomorphic feature, as it also occurs in Nannochoristidae. Features of the larval head of Trichoceridae, which were included in Tipulomorpha, do not show affinities with those of Tipuloidea. Trichocerid larvae share a specialised subdivided mandible with larvae of psychodomorph groups. Tipuloidea are a highly specialised group. The characters examined did not reveal plesiomorphic features supporting a basal position, and features suggesting closer affinities with Brachycera are vague. The evolution of dipteran larval head structures was apparently strongly affected by the loss of legs and the tendency to live in cryptic habitats. Diptera are the group of Endopterygota with the highest number of apomorphic features of the larval head. The appendages are generally simplified and the muscular apparatus is strongly reduced. Specialised features evolving within dipteran lineages include specifically arranged brushes of hairs on the labrum and epipharynx, movable messores, subdivided mandibles, different mandibular brushes, and a far-reaching reduction of labial parts.     

Fungal biodiversity in aquatic habitats

Fungal biodiversity in freshwater, brackish and marine habitats was estimated based on reports in the literature. The taxonomic groups treated were those with species commonly found on submerged substrates in aquatic habitats: Ascomycetes (exclusive of yeasts), Basidiomycetes, Chytridiomycetes, and the non-fungal Saprolegniales in the Class Oomycetes. Based on presence/absence data for a large number and variety of aquatic habitats, about 3,000 fungal species and 138 saprolegnialean species have been reported from aquatic habitats. The greatest number of taxa comprise the Ascomycetes, including mitosporic taxa, and Chytridiomycetes. Taxa of Basidiomycetes are, for the most part, excluded from aquatic habitats. The greatest biodiversity for all groups occurs in temperate areas, followed by Asian tropical areas. This pattern may be an artifact of the location of most of the sampling effort. The least sampled geographic areas include Africa, Australia, China, South America and boreal and tropical regions worldwide. Some species overlap occurs among terrestrial and freshwater taxa but little species overlap occurs among freshwater and marine taxa. We predict that many species remain to be discovered in aquatic habitats given the few taxonomic specialists studying these fungi, the few substrate types studied intensively, and the vast geographical area not yet sampled.     

Spatial autocorrelation and dispersal limitation in freshwater organisms

Dispersal can limit the ranges of species and the diversity of communities. Despite its importance, little is known about its role in freshwater habitats and its relation to habitat type (lentic vs. lotic), especially for organisms with cryptic dispersal methods such as plankton. Poor dispersers are expected to show more clumped distributions or greater spatial autocorrelation (SA) in community composition than good dispersers. We examined patterns of SA across freshwater taxa with different dispersal modes (active vs. passive) and their association with habitat type (lake vs. stream) using 18 spatially explicit community composition data sets. We found significant relationships between SA and body size among taxa in lake habitats, but not in streams. However, the increase in SA with body size in lakes was driven entirely by fishes—organisms ranging in size from diatoms to macro-invertebrates showed equivalent levels of SA. These results support the idea that large organisms are less effective dispersers in aquatic environments, resulting in greater SA in community structure over broad scales. Streams may be effectively more connected than lakes as patterns of SA and body size were weaker in lotic habitats. Our data suggest that the critical threshold where greater body size increases dispersal limitation seems to come at the juncture between invertebrates and vertebrates rather than that between unicellular and multicellular organisms as has been previously suggested. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The complete mitochondrial genome of Nephrotoma scalaris parvinotata (Brunetti 1918) (Diptera: Tipulidae) and insights into the phylogeny of Tipulomorpha

Craneflies (Tipuloidea or Tipulidae sensu lato) are one of the most diverse groups of true flies (Insecta, Diptera). The Tipuloidea and perhaps the Trichoceridae formed the infraorder Tipulomorpha, which is traditionally considered the most basal group of Diptera. Relationships among Tipulomorpha and the phylogenetic position of this infraorder within the whole Diptera remain to be settled. A mitochondrial genome (mitogenome) phylogeny of Diptera was produced to test the relationships within Tipulomorpha and its phylogenetic position. A complete mitogenome of Nephrotoma scalaris parvinotata (Tipuloidea, Tipulidae) was firstly sequenced with a next-generation sequencing approach. Compared with the published mitogenomes of Tipuloidea, the new mitogenome had a larger genome size (17,862 nt), due to a longer non-coding control region. The gene order was identical to Drosophila yakuba. Phylogenetic reconstructions using different inference methods recovered Tipulomorpha as monophyletic. And the Tipulomorpha was retrieved in a relatively basal position in Diptera. Within Tipulomorpha, the Tipuloidea and the Trichoceridae were strongly supported as reciprocally monophyletic. Relationships within Tipuloidea were resolved as (Pedicidae + (Limoniidae + (Cylindrotomidae + Tipulidae))). Well supported relationships include: Pedicidae was the sister group of (Limoniidae + (Tipulidae + Cylindrotomidae)); Limoniidae was paraphyletic with respect to (Tipulidae + Cylindrotomidae); Cylindrotomidae was the sister group of Tipulidae. The newly sequenced N. scalaris parvinotata clustered with other two Nephrotoma species at a derived position in Tipuloidea.     

Global diversity of oribatids (Oribatida: Acari: Arachnida)

Oribatid mites are primarily terrestrial. Only about 90 species (less than 1% of all known oribatid species) from 10 genera are truly aquatic, with reproduction and all stages of their life cycle living in freshwater. Adaptation to aquatic conditions evolved independently in different taxa. However, many terrestrial species can also be found in aquatic habitats, either as chance stragglers from the surrounding habitats, or from periodic or unpredictable floodings, where they can survive for long periods. In spite of their low species richness aquatic oribatids can be very abundant in different freshwater habitats as in lentic (pools, lakes, water-filled microhabitats) or flowing waters (springs, rivers, streams), mainly on submerged plants. The heavily sclerotized exoskeletons of several species enables subfossil or fossil preservation in lakes or bog sediments. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

New insights into and limitations of the molecular phylogeny in the taxon-rich land snail genus Montenegrina (Mollusca: Gastropoda: Clausiliidae)

Rock-dwelling gastropods are usually patchily distributed in limestone habitats, presumably have low active and passive dispersal ability and often represent narrow-ranged endemic taxa. Their current taxonomy is predominantly shell morphology based, and it remains unknown whether the morphologically differentiated and geographically separated populations represent phylogenetic clades. In this study, we analysed the hyperdiverse, terrestrial door snail genus Montenegrina. Based on the current taxonomy defined by shell morphology, it contains 29 species and 106 subspecies distributed in the Balkan region. The constructed phylogenetic tree using three mitochondrial markers was used to test whether it agrees with the current taxonomy. In this comprehensive tree, about half of the species and subspecies are monophyletic. Some of the paraphylies could be reasonably resolved by taxonomic changes; that is, some subspecies should be reassigned or raised to species level. Other incongruencies probably arose due to introgression even between distant clades. The histone genes turned out to be unsuitable for elucidating the phylogeny of Montenegrina. In the species-delimitation tests, considerably more molecular operational taxonomic units were delimited than the number of presently described species. The present data indicate that (a) shell morphology-based taxonomy and taxon recognition can be problematic in such a large and morphologically highly variable genus; (b) the potential error due to incomplete sampling presents a problem in a genus as variable as Montenegrina; (c) multi-locus analyses should be conducted to arrive at a better basis for species delimitation; and (d) integrative approaches including genetic as well as morphological/anatomical data from a comprehensive geographic sample are necessary.     

Adult aquatic insects: Potential contributors to riparian food webs in Australia's wet–dry tropics

Abstract Changes in the abundance and biomass of aquatic and terrestrial aerial insects with distance (mid‐stream, 0, 10–15 and 160 m) from lowland streams were examined across the dry season landscape in Kakadu National Park, northern Australia. Malaise traps and sticky intercept traps were used to sample the insects at four streams, spaced over an area of 1650 km². Malaise and intercept catches were dominated by Diptera (flies and midges), both numerically and by biomass. Chironomid midges were the most abundant taxon, making up 43.4 and 51.0% of the malaise and intercept trap catches, respectively. However, most chironomids were small (less than 3 mm body length), contributing 34.9% to intercept trap biomass, but only 5.2% in malaise traps. Ceratopogonid midges and caddisflies (Trichoptera) accounted for most of the remaining adult aquatic insects. Major terrestrial components were Diptera and Hymenoptera in malaise traps and Coleoptera and Diptera in intercept traps. The total abundance and biomass of insects were much greater over streams and along the water's edge than in riparian (10–15 m) and savanna (160 m) habitats primarily because of the presence of large numbers of adult aquatic insects. The abundance and biomass of terrestrial insects in malaise traps showed no relationship with distance, but intercept trap catches suggested slightly greater abundances over the water and at the water's edge. The great abundance of aquatic insects relative to terrestrial insects close to streams suggests that they have the potential to be an important component of the diets of riparian insectivores, and predation may be an important pathway by which aquatic nutrients and energy are moved into terrestrial food webs.