Description of two species of free-living nematodes (Nematoda) from fresh waterbodies of Vietnam

The new nematode species Monhystera longivaginata sp. n. and the rare species Mononchulus nodicaudatus (Daday, 1901) collected in waterbodies of Vietnam are described. M. longivaginata sp. n. is morphologically similar to M. paludicola de Man, 1881, but differs from it in a longer and slenderer tail in females, ocelli situated closer to the anterior end of the body, the presence of a postvulval gland cell, and a longer vagina. The genus Monhystera Bastian, 1865 is revised, and several species of this genus (M. lemani Juget, 1969, M. macramphus Filipjev, 1923, M. amabilis Gagarin, 1997, M. hamata Gagarin et Nguyen Vu Thanh, 2005, and M. melnikae Gagarin et Naumova, 2010) are transferred to the genus Eumonhystera Andrássy, 1981 as E. lemani (Juget, 1969) comb. nov., E. macramphus (Filipjev, 1929) comb. nov., E. amabilis (Gagarin, 1997) comb. nov., E. hamata (Gagarin et Nguyen Vu Thanh, 2005) comb. nov., and E. melnikae (Gagarin et Naumova, 2010) comb. nov.     

The consortium of the sponge Lubomirskia baicalensis in Lake Baikal,East Siberia

The spatial distribution of the fauna associated with a branched sponge, Lubomirskia baicalensis, endemic of Lake Baikal has been quantitatively studied. The biomass and numbers of three amphipod species which inhabit the sponge correlate (linearly or non-linearly) with the weight of the sponge.     

Free-living nematodes of the Tra Ly River in the Red River mouth,Vietnam

In samples of the Tra Ly River in the Red River mouth (Northern Vietnam), 46 species of free-living nematodes have been found, five of which are new to science. The species dominant in abundance were Ptycholaimellus adocius Dashchenko et Belogurov, 1984; Dichrocuadora affinis Gagarin et Nguyen Vu Thanh, 2011; and Tripyloides minor sp.n. The species composition of nematodes is listed and the new species Tripyloides minor sp. n. is described and illustrated. The nematode described and illustrated by Riemann (1970) from watercourses of Colombia as Tripyloides amazonicus (Gerlach, 1957) is recognized as a valid species (Tripyloides riemanni nom.n).     

Microsporidian Parasites Found in the Hemolymph of Four Baikalian Endemic Amphipods

At present, approximately 187 genera and over 1300 species of Microsporidia have been described, among which almost half infect aquatic species and approximately 50 genera potentially infect aquatic arthropods. Lake Baikal is the deepest and one of the oldest lakes in the world, and it has a rich endemic fauna with a predominance of arthropods. Among the arthropods living in this lake, amphipods (Crustacea) are the most dominant group and are represented by more than 350 endemic species. Baikalian amphipods inhabit almost all depths and all types of substrates. The age and geographical isolation of this group creates excellent opportunities for studying the diversity, evolution and genetics of host-parasite relationships. However, despite more than 150 years of study, data investigating the microsporidia of Lake Baikal remain incomplete. In this study, we used molecular genetic analyses to detect microsporidia in the hemolymph of several endemic species of amphipods from Lake Baikal. We provide the first evidence that microsporidian species belonging to three genera (Microsporidium, Dictyocoela and Nosema) are present in the hemolymph of Baikalian endemic amphipods. In the hemolymph of Eulimnogammarus verrucosus, we detected SSU rDNA of microsporidia belonging to the genus Nozema. In the hemolymph of Pallasea cancellous, we found the DNA of Microsporidium sp. similar to that in other Baikalian endemic amphipods; Dictyocoela sp. was found in the hemolymph of Eulimnogammarus marituji and Acanthogammarus lappaceus longispinus.     

Speciation of sponges in Baikal-Tuva region: an outline

Lake Baikal is known for its high percentage of endemic fauna and flora. The most abundant sessile animal taxa in the littoral zone of Baikal are the photosymbiotic sponges. These endemic sponges are grouped to the family Lubomirskiidae and are separated, based on molecular data, from the cosmopolitan family Spongillidae Gray 1867. In the present review, recent data on the potential driving forces of the rapid speciation in Lake Baikal have been unified. Current data suggest that the genetic repertoire of the sponges was sufficiently large to cope with the major cold events, occurring 2.8–2.5 and 1.8–1.5 Ma. It is proposed that during those periods of climatic incisions founder populations were separated from the parental cosmopolitan sponge population and developed subsequently to the array of endemic species. To clarify whether the endemic sponge fauna is indeed restricted to Lake Baikal only or whether there exist related taxa in other lakes, a collection of sponges in the 750 km distant Lake Chagytai was performed. This lake harbours unexpectedly large populations of the endemic species Baikalospongia dzhegatajensis . As the habitat of the Lake Chagytai (algal habitat) differs strongly from that of Lake Baikal (rocky habitat), it is proposed that after the formation of the initial founder population in response to the climatic shift, subsequent speciation was driven by habitat differences.     

Heat shock proteins in the mechanisms of stress adaptation in Baikal amphipods and palearctic <Emphasis Type="Italic">Gammarus lacustris</Emphasis> Sars. I. HSP70 family

The participation of HSP70 family proteins in the mechanisms of stress adaptation under thermal and toxic stress in Baikal endemic and palearctic organisms was investigated. The four Lake Baikal endemic species Gmelinoides fasciatus (Stebb.), Eulimnogammarus cyaneus (Dyb.), E. vittatus (Dyb.), Ommatogammarus fl avus (Dyb.) were compared with the palearctic fauna representative Gammarus lacustris Sars. The type of synthesis of HSP70 family heat shock proteins under thermal (exposure at a temperature of 20, 25, and 30°C) and toxic (exposure in CdCl₂ solutions with the concentrations 50, 10, 5, 0.5, and 0.05 mg/l) stress was determined. All species under investigation were shown to have a common trend towards HSP70 content increase; therewith some species-specific characteristics of the type of synthesis of the protein under investigation were observed. The conclusion has been made on HSP70 participation in the mechanisms of thermal and toxic resistance in the studied amphipod species.     

Echiuropus bekmanae n.sp. (Crustacea, Amphipoda, Carinogammaridae) from Lake Baikal, retrieved by a new deep-water sampling device

Lake Baikal is well known for its exceptional diversity of gammarid amphipods, with 95% of endemics from its 270 described species representing about 20% of the world freshwater fauna. Echiuropus (Asprogammarus) bekmanae n.sp. was collected by an `autonomous trap system', a sampling device thoroughly described here. Although not necrophagous itself, this new species was found in two baited trap samples (at 750 and more than 1600 m) from 1995 and 1996. This rather small (13 mm) deep water species is the eighth species of the subgenus Asprogammarus, of the Baikal endemic genus Echiuropus. Diagnoses of the subgenus and the closer species are given.     

Nematodes from saline and freshwater lakes of the Vestfold Hills,East Antarctica,including the description of <Emphasis Type="Italic">Hypodontolaimus antarcticus</Emphasis> sp. n.

The invertebrate fauna of many Antarctic ice-free areas, even those close to permanent research stations, can be poorly known. Here we describe some nematodes from freshwater and saline, marine-derived lakes of the Vestfold Hills, East Antarctica. The freshwater lakes contained the widespread East Antarctic endemic species, Plectus frigophilus Kirjanova, 1958. The saline lakes were inhabited by two recently described species, Halomonhystera halophila Andrássy, 2006 and Halomonhystera continentalis Andrássy, 2006, and by a new species described in this report, Hypodontolaimus antarcticus sp. n. Originally marine but now brackish Highway Lake contained a nematode fauna with both freshwater and marine-derived components. The nematode fauna of Antarctica now consists of 54 named species, 22 of which are found in East Antarctica.     

Two Radix spp. (Gastropoda: Lymnaeidae) endemic to thermal springs around Lake Baikal represent ecotypes of the widespread Radix auricularia

In this study, we re‐examine two species of freshwater gastropods of the genus Radix Montfort, 1810 (family Lymnaeidae), endemic to the geothermal springs in the Lake Baikal region in the southern part of eastern Siberia — Lymnaea (Radix) hakusyensis Kruglov et Starobogatov, 1989, and Lymnaea (Radix) thermobaicalica Kruglov et Starobogatov, 1989. The alleged species status of these endemics has been re‐assessed by means of an integrative approach combining molecular genetic taxonomy techniques with the traditional methods based on shell and soft body morphology. Phylogenetic reconstructions were made using both mitochondrial (COI) and nuclear (ITS2) DNA markers. We used topotypic samples of both species and specimens sampled from other sites around Lake Baikal. The results demonstrate that the two endemic species are only synonyms of a widespread Holarctic species, Radix auricularia (Linnaeus, 1758), and represent its intraspecific morph (ecotype) adapted to living in thermal springs. A new synonymy is proposed: Thermoradix Kruglov et Starobogatov, 1989 = Radix Montfort, 1810 (syn. n.).     

Study on the Lake Baikal microbial community in the areas of the natural oil seeps

We studied the composition of a natural microbial community, the distribution of different groups of microorganisms (including those able to degrade oil hydrocarbons) within the areas of natural oil seeps in the Lake Baikal. It was revealed that, in the bottom sediments, the oil-degrading microorganisms dominating the community have included the bacteria of g. Bacillus, while in the water column, dominating microbes are presented by species of genera Rhodococcus, Pseudomonas, and Micrococcus. Under the conditions of the model experiment, the potential activity of Baikal microbes towards utilization of n-alcanes has been assessed. Under such conditions it was shown that the concentration of n-alcanes decreases to 60% during 20 days of the experiment (the initial oil concentration was 0.5 mg/l, i.e., ten maximal permissible concentrations, MPC).     

A transcriptome-wide assessment of differentially expressed genes among two highly divergent,yet sympatric,lineages of the freshwater Atyid shrimp, <Emphasis Type="Italic">Paratya australiensis</Emphasis>

The current study evaluated the possible toxic effects of the water-soluble fraction of crude oil on the general cellular stress-response mechanisms of two dominant representatives of Lake Baikal’s littoral community, the endemic amphipod species Eulimnogammarus verrucosus and E. cyaneus. The acute toxicity effects on the cellular stress-response mechanisms of amphipods were studied in the laboratory by exposing amphipods in water from Lake Baikal to addition of a water-soluble fraction of crude oil at concentrations considered safe for the aquatic environment. The present study found that even short-term exposure to a water-soluble fraction of crude oil at concentration of 50 µg/L, established as the threshold limit for fishery and aquaculture water reservoirs in the Russian Federation, directly affected the general stress-response markers HSP70 and lipid peroxidation and significantly changed the activity of antioxidant enzymes in both studied species. This result confirms the high sensitivity of Baikal endemics to crude oil. Thus, it also indicates that established standards and threshold limit values of oil concentrations estimated for ecological monitoring of general water reservoirs cannot be applied directly to the unique Lake Baikal ecosystem.     

Molecular evolution of the Lake Baikal endemic caddisflies (Trichoptera)

Phylogenetic relationships of the nine Lake Baikal endemic caddisfly species with the representatives of the genus Apatania (Apataniidae) were reconstructed on the basis on nucleotide sequences of the mitochondrial COI gene. The results of Bayesian analysis pointed to the relationships of the endemics with the North American Apatania incerta (Banks, 1897) and A. sorex (Ross, 1941). The divergence of the genetic lineages of the Baikalian and Nearctic apataniids occurred in the Late Oligocene–Early Miocene. On the dendrogram, endemic species formed two monophyletic clades corresponding to the tribes Thamastini and Baicalinini. It was also found that the genus Protobaicalina was polyphyletic, while the genus Baicalina was a species flock. Our analysis showed that the nearest common ancestor of the studied Baikal caddisfly species existed about 21 Mya, while the modern species composition of endemic fauna dates back to Pliocene–Pleistocene age (2.5–0.7 million years).     

A faunistic review of carabids (Coleoptera,Carabidae) of the Barguzin Mt. Range (Northern Baikal Area)

The list of carabids from the Barguzin Mt. Range includes 132 species belonging to 29 genera of 17 tribes. Five new species endemic or subendemic to the Barguzin Mt. Range have been discovered. The carabid fauna of the Northern Baikal Area has a high percentage of species with wide distribution in the Palaearctic. The bulk of the fauna consists of species with Circumholarctic, Transpalaearctic, Euro-Siberian, Siberian, and Asian-American ranges. Sayano-Baikalian, Southern Siberian, Baikalian, and Transbaikalian species with local distribution are less numerous than the Mongolian, Kazakhstan, Amur, and Okhotian species. Lake Baikal and mountain ranges framing it form a meridional barrier for the distribution of some species.     

The endemic Cladophorales (Ulvophyceae) of ancient Lake Baikal represent a monophyletic group of very closely related but morphologically diverse species

Lake Baikal, the oldest lake in the world, is home to spectacular biodiversity and extraordinary levels of endemism. While many of the animal species flocks from Lake Baikal are famous examples of evolutionary radiations, the lake also includes a wide diversity of endemic algae that are not well investigated with regards to molecular‐biological taxonomy and phylogeny. The endemic taxa of the green algal order Cladophorales show a range of divergent morphologies that led to their classification in four genera in two families. We sequenced partial large‐ and small‐subunit rDNA as well as the internal transcribed spacer region of 14 of the 16 described endemic taxa to clarify their phylogenetic relationships. One endemic morphospecies, Cladophora kusnetzowii, was shown to be conspecific with the widespread Aegagropila linnaei. All other endemic morphospecies formed a monophyletic group nested within the genus Rhizoclonium (Cladophoraceae), a very surprising result, in stark contrast to their morphological affinities. The Baikal clade represents a species flock of closely related taxa with very low genetic differentiation. Some of the morphospecies were congruent with lineages recovered in the phylogenies, but due to the low phylogenetic signal in the rDNA sequences the relationships within the Baikal clade were not all well resolved. The Baikal clade appears to represent a recent radiation, based on the low molecular divergence within the group, and it is hypothesized that the large morphological variation results from diversification in sympatry from a common ancestor in Lake Baikal.     

Oligochaeta and Aphanoneura in ancient lakes: a review

By their antiquity, history, rarity, great depth in many instances and the presence of highly diverse faunas with many endemics, ancient lakes constitute ecosystems of a special nature, clearly apart from the large majority of extant lakes. While the fauna of these lakes is becoming better and better known for various animals groups, the Oligochaeta are still poorly known. Tubificidae and Naididae are found in each ancient lake. On the other hand, some families are restricted to only one lake, such as Aeolosomatidae and Proppapidae in Lake Baikal or Eudrilidae and Ocnerodrilidae (megadriles) in Lake Tanganyika, but such a distribution is probably due to a lack of knowledge or sampling biases. All ancient lakes have an endemic oligochaete fauna except Lake Kinneret (Israël). The oldest, Lake Baikal (20–25 Ma), holds the most abundant and diverse oligochaete fauna, in which species flocks are even recognizable or suspected. In contrast, the oligochaete fauna of the slightly younger Lake Tanganyika is very scarce. This is partly due to an obvious lack of studies, as the oligochaete fauna of other great African lakes is virtually unknown, but this might be the result of an environment in these lakes less favourable to oligochaetes. Some factors likely to interact with speciation in oligochaetes are discussed but nothing can be concluded to date. A recent interest in African great lakes revealed a more diverse oligochaete fauna than previously assumed but a better study of this fauna is still badly needed.     

Phylogeny of the endemic Baikalian Sergentia (Chironomidae,Diptera)

Fragments of two mitochondrial genes, cytochrome b (CytB) and Cytochrome c oxidase subunit I (COI) have been used as phylogenetic markers in Sergentia (Chironomidae, Diptera). The concatenated (1241 bp) sequences from both genes were used to infer the phylogenetic relationships among seven Sergentia species. Five of the species belong to the endemic fauna of Lake Baikal. Alignments of the nucleotide sequences were used for the construction of trees using Neighbor-Joining and maximum parsimony methods. Both methods yielded similar results. Monophyly of both Sergentia and the Baikalian endemic species was well supported. The date of origin of the endemic group of Sergentia was estimated as 25.7 MYA which closely coincides with the start of geological changes in the Baikal area. A cytological tree, based on 12 chromosomal characteristics, for the same set of Sergentia species showed a great similarity to the molecular phylogeny.