Validating Livanow: molecular data agree that leeches, Branchiobdellidans, and Acanthobdella peledina form a monophyletic group of oligochaetes.

To investigate the phylogenetic relationships of leeches, branchiobdellidans, and acanthobdellidans, whole nuclear 18S rDNA and over 650 bp of mitochondrial cytochrome c oxidase subunit I were acquired from 101 annelids, including 36 leeches, 18 branchiobdellidans, Acanthobdella peledina, as well as 28 oligochaetes and combined with homologous data for 17 polychaete outgroup taxa. Parsimony analysis of the combined aligned dataset supported monophyly of leeches, branchiobdellidans, and acanthobdellidans in 100% of jackknife replicates. Monophyly of the oligochaete order Lumbriculida with Acanthobdellida, Branchiobdellida, and Hirudinea was supported in 84% of jackknife replicates. These results provide support for the hypotheses that leeches and branchiobdellidans are sister groups, that acanthobdellidans are sister to them, and that together with the family Lumbriculidae they all constitute a clade within Oligochaeta. Results support synonymy of the classes Clitellata and the more commonly used Oligochaeta. Leeches branchiobdellidans, and acanthobdellidans should be regarded as orders equal to their closest relatives, the order Lumbriculida.     

Graylings of Baikal Lake basin (Thymallus, Thymallidae): Diversity of forms and their taxonomic status

The morphological characters, molecular-genetic features, and patterns of the dorsal fin in different subspecies and forms of Arctic grayling Thymallus arcticus populating Lake Baikal and its tributaries, Irkutsk Reservoir, and Lake Khubsugul have been studied. Three groups are discernable. The first includes the white and black Baikal graylings T. a. baicalensis, as well as the western Siberian T. a. arcticus; the second group is represented by the Kosogol grayling T. a. nigrescens, and the third is composed of T. arcticus ssp. from the Yakchii lakes (the Verkhnyaya Angara basin) with a phenotype close to graylings populating the upper reaches of the Lena River. All of them are distinguished by some morphological characters, elements of the dorsal fin pattern, and by body coloration. The populations of black Baikal graylings are genetically uniform, and their distinctions from white Baikal graylings are insignificant, which agrees with the absence of a considerable divergence of these forms by a complex of meristic characters. It is assumed that in the black and white Baikal graylings the exchange by genetic information has either ceased quite recently, or persists, although, insignificantly. Some genetic remoteness of the west Siberian grayling from Irkutsk Reservoir and Nizhnyaya Tunguska, closely related to the Baikal grayling, is recorded. The formation of the Khubsugul subspecies is possibly a result of the contact of grayling populations during the rearrangements of the river system in the last glaciation period in the upper reaches of Yenisei and Selenga in Mongolia. The habitation in the Baikal system of the Upper Lena graylings indicates a connection between the Lena and Baikal basins in the past. The results of a multivariate analysis of meristic characters and the sequences of mitochondrial DNA confirm the conclusion made by Svetovidov (1931, 1936), concerning the absence of grounds to assign a species status to the Baikal forms.     

Cholera phages from open reservoirs of the Lake Issyk-Kul basin and their taxonomy]

In the water of open water bodies in the basin of Lake Issyk-Kul the presence of Vibrio cholerae belonging to group O1 and other groups and V. cholerae phages of known serotypes, as well as phages of a new type having no serological and morphological analogs in the current classification of V. cholerae phages, has been established. On the basis of analysis of inaccuracies appearing in the determination of the specificity of V. cholerae phages their systematization within the adequate unified classification of vibriophages is proposed.     

Microorganisms in the Sediments of Lake Baikal,the Deepest and Oldest Lake in the World

Microbiology - The review summarizes the results of recent studies of microbial communities of the Lake Baikal sediments obtained using diverse techniques. In the sediments of the areas of stable...     

Molecular phylogeny of pontobdelline leeches and their place in the descent of fish leeches (Hirudinea, Piscicolidae)

Phylogenetic relationships of all genera of the fish leech subfamily Pontobdellinae were investigated using mitochondrial (12S rDNA, COI, tRNA-Leu, ND1) and nuclear (28S rDNA) DNA sequences under maximum likelihood, Bayesian inference and parsimony. All methods resulted in trees that corroborated the monophyly of the family Piscicolidae, but recovered their subfamily Pontobdellinae as non-monophyletic. Based on the basal position of the giant Antarctic Megaliobdella szidati , it is hypothesized that the putative ancestor of fish leeches was a free-ranging, large bodied, muscular leech. The next branch contains parasites of cartilaginous fishes, Pontobdella muricata and Pontobdella macrothela . Two remaining genera of the subfamily (the Arctic Oxytonostoma and the Antarctic Moorebdellina ) showed weak affinities to other piscicolid taxa. The obtained phylogenetic hypothesis suggests a possible transition from an ancestral free-ranging life style and temporary parasitism, to parasitism on cartilaginous fishes, followed by parasitism on bony fishes.     

Vertical planktonic structure in the central basin of Lake Baikal in summer 1999, with special reference to the microbial food web

Planktonic microbial interactions in the central basin of Lake Baikal were examined on a summer day in 1999. The subsurface maxima of bacterial abundance and chlorophyll concentration were recorded at the same depth, whereas the vertical distribution of heterotrophic nanoflagellates was the inverse of those of bacteria and picophytoplankton. Release of extracellular organic car-bon (EOC) from phytoplankton was estimated by the NaH¹⁴CO₃ method as 2.4µgCl^–1day^–1. Bacterial production (4.3µgCl^–1day^–1), estimated in a bottle incubation experiment using size-fractionated water samples, exceeded the EOC released. Thus, other supplying sources of organic matter are needed for the bacterial production. Grazing (2.6µgCl^–1day^–1) was also estimated in the experiment and accounted for 60% of the bacterial production. This is the first report on the microbial food web in the central basin of Lake Baikal.     

Carotenoids, photoprotection and food web links in Lake Baikal

1. Carotenoids were extracted from macrophytes, sponges, amphipods, fish stomachs, fish livers, fish ovaries and zooplankton in samples collected from various depths in Lake Baikal. 2. Acetone extracts from macrophytes showed a ratio of absorption at wavelengths of 430 and 665 nm consistently in the range 2.1–2.5. Sponges from very shallow water (1.5m) showed a similar ratio, but a sponge from 25m gave a ratio of 6.6, indicating a reduction in the concentration of chlorophyll relative to carotenoids. 3. Extracts from amphipods gave some support for the photoprotection hypothesis, with lower concentrations of carotenoids in amphipods from the deepest water. 4. Some fish took high concentrations of carotenoids into their stomachs, but the concentrations found in their Livers and ovaries were very much lower. Fish appear to be one of the carotenoid sinks in Lake Baikal. 5. Plankton samples showed an apparent inversion, with the highest concentration of carotenoid in the deepest sample, but this was a result of the sinking into deep water of the filamentous diatom Melosira.     

Molecular-phylogenetic analysis of cyclopoids (Copepoda: Cyclopoida) from Lake Baikal and its water catchment basin

Baikalian cyclopoids represent one of the richest endemic faunas of freshwater cyclopoid copepods. The genus Diacyclops Kiefer, 1927 is the most numerous by species number in the lake. In this work, molecular-phylogenetic analysis of 14 species and 1 sub-species from Lake Baikal and its water catchment basin is performed. The regions of mitochondrial cytochrom-oxydase I (COI) and of nuclear small-subunit 18S rRNA were used as evolution markers. In the obtained set of COI gene sequences, an effect of synonymous substitution saturation is revealed. Baikalian representatives of the genus Diacyclops form at phylogenetic schemes by two markers a monophyletic group, it suggest their origin from a common ancestral form. Preliminary estimate of this group age is 20–25 My.     

Lake-wide assessment of microplastics in the surface waters of Lake Baikal,Siberia

Limnology - Small microplastic particles < 330 µm, sometimes called mini-microplastics (MMP), are far more abundant than those larger than 330 µm....     

Photosynthetic potential of phytoplankton in the deep water of Lake Baikal,Russia

We examined the photosynthetic activity of the phytoplankton community collected from the surface to a depth of 1000m in the south basin of Lake Baikal. Experiments were conducted in June (mixing period) and August (stratified period). The carbon fixation rate was measured by the use of a ¹³C tracer after the incubation of samples under light conditions in the upper water column. Photosynthetic fixation of ¹³C was detected for samples collected from a depth of 500m, indicating the viability of phytoplankton in deep water. The community composition was dominated by Bacillariophyceae in deep water. The finding of lower activity at a depth of 200m than that at a depth of 500m in August suggests that the spring diatom bloom could be a significant source of viable populations at a depth of 500m. Photosynthetic activity was not detected in samples collected at a depth of 1000m.     

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.     

Abundance and composition of the summer phytoplankton community along a transect from the Barguzin River to the central basin of Lake Baikal

The abundance and composition of phytoplankton were investigated at six stations along a transect from the Barguzin River inflow to the central basin of Lake Baikal in August 2002 to clarify the effect of the river inflow on the phytoplankton community in the lake. The water temperature in the epilimnion was high near the shore at Station 1 (17.3°C), probably due to the higher temperature of the river water, and gradually decreased offshore at Station 6 (14.5°C). Thermal stratification developed at Stations 2–6, and a thermocline was observed at a 17–22-m depth at Stations 2–4 and an 8–12-m depth at Stations 5 and 6. The concentrations of nitrogen and phosphorus nutrients in the epilimnion at all stations were <1.0 μmol N l⁻¹ and <0.16 μmol P l⁻¹, respectively. Relatively high concentrations of nutrients (0.56–7.38 μmol N l⁻¹ and 0.03–0.28 μmol P l⁻¹) were detected in the deeper parts of the euphotic zone. Silicate was not exhausted at all stations (>20 μmol Si l⁻¹). The chlorophyll a (chl. a) concentration was high (>10 μg l⁻¹) near the shore at Station 1 and low (<3 μg l⁻¹) at five other stations. The <2 μm fraction of chl. a in Stations 2–6 ranged between 0.80 and 1.85 μg l⁻¹, and its contribution to total chl. a was high (>60%). In this fraction, picocyanobacteria were abundant at all stations and ranged between 5 × 10⁴ and 5 × 10⁵ cells ml⁻¹. In contrast, chl. a in the >2 μm fraction varied significantly (0.14–11.17 μg l⁻¹), and the highest value was observed at Station 1. In this fraction, the dominant phytoplankton was Aulacoseira and centric diatoms at Station 1 and Cryptomonas, Ankistrodesmus, Asterionella, and Nitzschia at Stations 2–6. The present study demonstrated the dominance of picophytoplankton in the pelagic zone, while higher abundance of phytoplankton dominated by diatoms was observed in the shallower littoral zone. These larger phytoplankters in the littoral zone probably depend on nutrients from the Barguzin River.     

Fatty acid composition in the white muscle of Cottoidei fishes of Lake Baikal reflects their habitat depth

Lake Baikal is a unique freshwater environment with maximum depths over 1600 m. The high water pressure at the lakebed strengthens the solidifying effect of low water temperature on animal tissue lipids, and thus the effective temperatures in the depths of the lake equal subzero temperatures in shallow waters. Cottoidei species has colonized the different water layers of the lake, and developed different ecology and physiology reflected in their tissue biochemistry. We studied by gas chromatography the composition of fatty acids (FAs), largely responsible for tissue lipid physical properties, in the white muscle tissue of 13 species of the Cottoidei fish; five benthic abyssal, six benthic eurybathic and two benthopelagic species. The FA profiles reflected habitat depth. The muscles of the deepest living species contained little polyunsaturated FAs (PUFAs) and were instead rich in monounsaturated FAs (MUFAs), which may be due to occasional weak food web links to the PUFA-rich primary producers of the photic water layer, high MUFA supply from their benthic diet, and conversion of saturated FAs (SFAs) to MUFAs in the tissues of the fish. Despite the MUFA percentage among the abyssal species reached even 50% (by weight) of total FAs, the PUFA percentage still remained above 20% in every species. The muscle MUFA/SFA ratio correlated negatively with the PUFA content of the fish muscle, suggesting viscosity control integrating the fluidity contributions from the dietary PUFAs and potentially endogenous MUFAs.     

Abundance and pigment type composition of picocyanobacteria in Barguzin Bay, Lake Baikal

In Lake Baikal, picocyanobacteria are the most important primary producers during the summer. Freshwater picocyanobacteria are discriminated into either the phycoerythrin (PE)-rich or the phycocyanin (PC)-rich types according to their pigment composition. The distributions of these two types of picocyanobacteria were investigated in Barguzin Bay. The PC-rich type accounted for >98% of the total picocyanobacteria at the station near the shore of the bay where river water flows directly in. In the offshore area of the lake, all of the picocyanobacteria cells were of the PE-rich type. In addition, the occurrence of the PC-rich type was restricted to the station, where the attenuation coefficient exceeded 0.25 m⁻¹. Near the shore, where the turbidity was high (>1 NTU), the cell densities of both the PE- and PC-rich types increased away from the river mouth. This indicates that the PC-rich type cells grow near the shore of the bay where turbidity is high. Since the PC-rich type could not grow well when cells were incubated in offshore lake water, restricted distribution of the PC-rich type could also be explained by their growth capability. The present study clearly demonstrated the shift in the pigment type composition of picocyanobacteria from the coastal to the pelagic zone of Lake Baikal. The co-existence of the two pigment types probably enables the abundance of the picocyanobacterial community to be stable over a broader range of environmental conditions than would be possible for a single pigment type.     

The morphological variability of the maritae of Phyllodistomum umblae and Phyllodistomum folium (Trematoda: Gorgoderidae) from fish in the Lake Baikal basin

The host variability of adults of Phyllodistomum umblae and P. folium in fishes of the Baikal region has been studied. The absence of considerable geographical variability of P. umblae in Coregonus lavaretus (Lake Baikal, Lake Storsj?n in Sweden) has been shown. The complexes of most stable (the size of acetabulum and eggs, location of acetabulum, ovary and vitelline bodies) and variable (the distance from oral sucker to intestinal bifurcation, distance from intestinal back edge to body end, width of seminal vesicle) features of trematodes of the genus Phyllodistomum have been determined.     

Regional, vertical and seasonal distribution of phytoplankton and photosynthetic pigments in Lake Baikal

A 3-year phytoplankton study was carried out in Lake Baikal(Siberia) as part of the CONTINENT project and in conjunctionwith a 60-year long monitoring programme by the Irkutsk StateUniversity. A combination of microscopy and high performanceliquid chromatography (HPLC) pigment analysis was used. Allover the lake, the dominant functional group (by biovolume)was the vernal diatom blooms, due to the dominance of endemicCyclotella species. Chlorophyll a (Chl a) was significantlyhighest at the Selenga and Barguzin inflows (2.39 ± 0.34and 2.49 ± 0.18 nmol L^–1, mean ± 95% CI,respectively) and higher in the South than in the North (1.43± 0.26 and 0.96 ± 0.13 nmol L^–1). This variationof Chl a reflected changes in the phytoplankton composition.Diatoms and Chrysophyceae were the major contributors to thetotal Chl a except in the South (Chlorophyceae) and SelengaDelta (cyanobacterial picoplankton). There were also indicationsof species composition changes due to enhanced P-loading fromthe Selenga River. However, canonical analyses indicated thattemperature and stratification were the major driving forcesfor regional distribution patterns and seasonal succession.It seems likely that further global warming will cause a shiftin the species and group composition towards small cells atthe expense of the large endemic diatom flora.     

Drivers of ecosystem change and their impacts on human well-being in Lake Victoria basin

To offer an increased understanding of the spatial patterns, temporal, social and physical predictors of the conversion and transformations of land use in Lake Victoria basin, an assessment of proximate and underlying forces is presented. This study discusses key theoretical underpinnings for the manifold linkages existing between selected drivers of land-use changes around the basin and their consequences on human well-being. Using a meta-analytical research design, the paper analyses ecosystems level cases of the causes of land use and cover changes in the basin, to determine any spatio-temporal or institutional patterns and dynamics. A suite of recurrent core variables has been identified to influence land use and cover changes in the basin. The most prominent of these at the underlying category are climatic factors, economic factors, institutions, national and regional policies, population growth and other remote influences. At the proximate level, these factors drive cropland expansion, overgrazing, infrastructure extension and rates of land degradation. These are supported by empirical evidence from the basin. This assessment is crucial for appropriate local and transboundary policy interventions, which have to be fine-tuned to the locale-specific dynamic patterns associated with the inherent ecosystems changes.