Molecular phylogeny of the freshwater sponges in Lake Baikal

The phylogenetic relationship of the freshwater sponges (Porifera) in Lake Baikal is not well understood. A polyphyletic and/or monophyletic origin have been proposed. The (endemic) Baikalian sponges have been subdivided into two families: endemic Lubomirskiidae and cosmopolitan Spongillidae. In the present study, two new approaches have been made to resolve the phylogenetic relationship of Baikalian sponges; analysis of (1) nucleotide sequences from one mitochondrial gene, the cytochrome oxidase subunit I (COI) and of (2) one selected intron from the tubulin gene. Specimens from the following endemic Baikalian sponge species have been studied; Lubomirskia baicalensis , Baikalospongia intermedia, Baikalospongia recta , Baikalospongia bacillifera and Swartschewskia papyracea . They are all grouped to the family of Lubomirskiidae. Sequence comparisons were performed with the ubiquitously distributed freshwater sponge Spongilla lacustris (family Spongillidae) as well as with one marine sponge, Suberites domuncula . A sequence comparison * * The sequences reported here are being deposited in the EMBL data base. of the mitochondrial COI gene revealed a monophyletic grouping of the endemic Baikalian sponges with S. lacustris as the most related species to the common ancestor. The sequences of the COI gene from B. recta , B. intermedia , B. bacillifera and L. baicalensis were found to be identical and separated from those of S. lacustris and S. papyracea . In a second approach, the exon/intron sequences framing the intron‐2 of the sponge tubulin gene were chosen for the phylogenetic analysis. The intron sequences were aligned and used for construction of a phylogenetic tree. This analysis revealed again a monophyletic grouping with S. lacustris as the closest related species to the common ancestor. It is concluded that the Baikalian sponges, which have been studied here, are of monophyletic origin. Furthermore, the data suggest that the endemic species S. papyracea is the phylogenetically oldest, extant, endemic Baikalian sponge species.     

Expression of silicatein in spicules from the Baikalian sponge Lubomirskia baicalensis

Lake Baikal harbors the largest diversity of sponge species [phylum Porifera] among all freshwater biotopes. The abundantly occurring species Lubomirskia baicalensis was used to study the seasonal silicatein metabolism; the spicules of this species have an unusually thick axial filament, consisting of silicatein, which remains constant in diameter during their growth. In the course of maturation, the size of the silicic acid shell grows, until the final diameter of the spicules of about 8 microm is reached. The seasonal content of silicatein was assessed by use of antibodies raised against silicatein; they stained specifically the axial filaments. In addition we determined, by application of the enzyme-linked immunosorbent assay system, that the proteinaceous content of the spicules, the silicatein, increases from spring to late summer by 8-fold. As molecular markers to quantify the seasonal changes in expression levels of genes coding for proteins/enzymes, the genes for the calumenin-like protein and the kinesin-related protein, were selected. The expression of calumenin-like gene, involved in the intracellular signaling, is highest during September, whereas the expression of the kinesin-related protein does not change during the annual course. These results suggest that the highest metabolic activity of L. baicalensis occurs in late summer (September), in parallel with the highest accumulation of silicatein, a structural protein/enzyme of the spicules.     

The problem of germ layers in sponges (Porifera) and some issues concerning early metazoan evolution

Nowadays the formation of germ layers (endoderm and mesoderm) is associated with gastrulation. The question of whether the cell movements during early embryonic development in sponges (Porifera) are gastrulation as in eumetazoans remains in dispute. Recent data on the histological organization, digestion and embryonic morphogenesis in sponges are analyzed here in an attempt to answer this question. Unique features of these basal Metazoa are the lack of intestinal epithelium, digestive parenchyma or any cell population specialized in digestion. Food particles are captured by cells of almost all types. These data show that sponges have no embryonic layers such as ectoderm or endoderm, characteristic to eumetazoans, and, consequently, no gastrulation. We make an assumption that the formation of germ layers cannot be considered as a recapitulation of events that took place in the common ancestor of Porifera and Eumetazoa. The unity of Metazoa is expressed not in the presence of gastrulation processes per se, but in the universal nature of cell movement mechanisms ensuring various types of morphogenesis, including those underlying gastrulation. It is concluded that metazoan mechanisms of morphogenetic movements must have emerged in the course of evolution prior to the separation of the germ layers like endoderm and ectoderm.     

Benthic-pelagic coupling on coral reefs: Feeding and growth of Caribbean sponges

Benthic-pelagic coupling and the role of bottom-up versus top-down processes are recognized as having a major impact on the community structure of intertidal and shallow subtidal marine communities. Bottom-up processes, however, are still viewed as principally affecting the outcome of top-down processes. Sponges on coral reefs are important members of the benthic community and provide a crucial coupling between water-column productivity and the benthos. Other than scleractinian corals, sponges dominate many of these habitats where water column productivity is composed of mostly autotrophic and heterotrophic picoplankton that sponges actively filter. While predation upon sponges by invertebrates, fish, and turtles occurs, the sponges Callyspongia vaginalis, Agelas conifera, and Aplysina fistularis from Florida, Belize, and the Bahamas, respectively, exhibit a consistent and significant pattern of greater biomass, rates of growth, and feeding, as does their food supply, with increasing depth. Sponges consume 65-93% of the available particulate food supply and, at all sites, sponges increase in size and growth rate as depth increases, suggesting that food supply and, therefore, bottom-up processes significantly influence the distribution and abundance of sponges in these habitats.     

Advances in Ecological Speciation: an integrative approach

The role of natural selection in promoting reproductive isolation has received substantial renewed interest within the last two decades. As a consequence, the study of ecological speciation has become an extremely productive research area in modern evolutionary biology. Recent innovations in sequencing technologies offer an unprecedented opportunity to study the mechanisms involved in ecological speciation. Genome scans provide significant insights but have some important limitations; efforts are needed to integrate them with other approaches to make full use of the sequencing data deluge. An international conference ‘Advances in Ecological Speciation’ organized by the University of Porto (Portugal) aimed to review current progress in ecological speciation. Using some of the examples presented at the conference, we highlight the benefits of integrating ecological and genomic data and discuss different mechanisms of parallel evolution. Finally, future avenues of research are suggested to advance our knowledge concerning the role of natural selection in the establishment of reproductive isolation during ecological speciation.     

Spicule dimensions as taxonomic criteria in the identification of haplosclerid sponges from the shores of Anglesey

The lengths and widths of at least 100 spicules from each of 126 specimens, comprising at least 12 species of haplosclerid sponges, mainly from Church Island and Rhosneigr, Anglesey, North Wales have been measured. It was found that spicule dimensions by themselves would be unreliable in the identification of species. The sample means, medians and maxima, when plotted using width and length axes, form specific clusters that overlap, sometimes to a considerable extent. The correlation coefficients for width against length varied widely, even when single species were considered. The variation arises from differences in the numbers of juvenile spicules in various samples. The best correlation coefficients exceeded 0.8 and the regression constants for linear correlation in such samples could be useful in the diagnosis and taxonomy of the species. The coefficients of variation for length and width also yielded parameters for species characterization. In general the coefficient for length tended to increase as the mean length increased, whereas that for width tended to decrease with increasing mean width. Some species stood apart from the general trends, however. The coefficients varied widely from one sample to another of the same species, identified using a variety of diagnostic features. To some extent the variation was linked with the date of collection. When all the data were combined, the average coefficient for width decreased markedly in May. The same was true for two species that were separately considered. The decrease was not simply caused by a change in mean width, changes in standard deviation also being involved. There was a tendency for certain species, in particular Reniera rosea and Gellius angulatus , to produce thin spicules in the spring, which became incorporated distally in the primary spicule bundles in July-August.     

Phylogenetic analysis of freshwater sponges provide evidence for endemism and radiation in ancient lakes

Morphologic and phylogenetic analysis of freshwater sponges endemic to lakes in Central Sulawesi, Siberia and South-East Europe is presented. We also analyzed several cosmopolitan sponge species from Eurasia and North America and included sponge sequences from public databases. In agreement with previous reports [Addis, J.S., Peterson, K.J., 2005. Phylogenetic relationships of freshwater sponges (Porifera, Spongillina) inferred from analyses of 18S rDNA, COI mtDNA, and ITS2 rDNA sequences. Zool. Scr. 34, 549-557], the metaniid sponge Corvomeyenia sp. was the most deeply branching species within a monophyletic lineage of the suborder Spongillina. Pachydictyum globosum (Malawispongiidae) and Nudospongilla vasta (Spongillidae), two morphologically quite distinct species from Sulawesi were found in a joint clade with Trochospongilla (Spongillidae) rendering Trochospongilla paraphyletic. Furthermore, Ochridaspongia sp., another Malawispongiidae, clustered far away from that clade, together with Ephydatia fluviatilis, making the latter family polyphyletic. The Lubomirskiidae endemic to Lake Baikal, Lubomirskia abietina, Baikalospongia bacillifera, B. intermedia, and Swartschewskia papyracea formed a well-supported clade that was most closely linked to the genus Ephydatia (99.9% identity over a total length of 2169 concatenated nucleotide positions). Our study indicates the frequent and independent origin of sponge species endemic to different freshwater ecosystems from a few cosmopolitan founder species. The highly specific primer sets newly developed here facilitate work on the molecular phylogeny and DNA barcoding of sponges.     

Speciation in rapidly diverging systems: lessons from Lake Malawi

Rapid evolutionary radiations provide insight into the fundamental processes involved in species formation. Here we examine the diversification of one such group, the cichlid fishes of Lake Malawi, which have radiated from a single ancestor into more than 400 species over the past 700 000 years. The phylogenetic history of this group suggests: (i) that their divergence has proceeded in three major bursts of cladogenesis; and (ii) that different selective forces have dominated each cladogenic event. The first episode resulted in the divergence of two major lineages, the sand- and rock-dwellers, each adapted to a major benthic macrohabitat. Among the rock-dwellers, competition for trophic resources then drove a second burst of cladogenesis, which resulted in the differentiation of trophic morphology. The third episode of cladogenesis is associated with differentiation of male nuptial colouration, most likely in response to divergent sexual selection. We discuss models of speciation in relation to this observed pattern. We advocate a model, divergence with gene flow, which reconciles the disparate selective forces responsible for the diversification of this group and suggest that the nonadaptive nature of the tertiary episode has significantly contributed to the extraordinary species richness of this group.     

Variation in clone structure of fragmenting coral reef sponges

Populations of three branching Caribbean demosponge species are composed of clones produced by asexual fragmentation. Dispersal of the fragments before they become established as independent individuals scatters clone members widely and intermixes members of different clones, complicating study of the clone structure of these populations and contrasting with many other sessile clonal organisms. Clone structures of these populations were inferred using a combination of tissue-compatibility relationships and an analysis of variations in morphology and colour. Although tissue compatibility cannot be used for precise identification of sponge clones, in general, patterns of variation in morphological characters influencing fragmentation and patterns of fragment dispersal and recruitment suggest that, in these populations, tissue-compatibility relationships closely reflect clone structure. Conditions that must be met in order to use tissue compatibility for study of sponge clones are discussed, and previous results, from which conflicting conclusions have been drawn, reconciled in this context. Variations among clones in numbers of physiologically independent members and in size and shape of areal extent are discussed in the context of processes that may affect evolution of clonal characters in these populations and in other species that propagate by dispersing asexual fragments.     

Lipid compounds of freshwater sponges: family Spongillidae,class Demospongiae

More than 100 novel, unusual and rare fatty acids, lipids and sterols have been isolated from freshwater sponges. The structures, biogenesis, synthesis and bioactivity of some lipid compounds of freshwater sponge species are reviewed.     

Genome size and chromosomes in marine sponges [Suberites domuncula,Geodia cydonium]

The genome size of the marine sponges Suberites domuncula and Geodia cydonium has been determined by flow cytofluorometric analysis using diamidino-phenylindole [DAPI]. Using human lymphocytes as reference the amount of DNA in cells from S. domuncula has been determined to be 3.7 pg and that of G. cydonium 3.3 pg. While no chromosomes could be identified in G. cydonium, the karyotype of the Suberites domuncula is 32 chromsomes in the diploid state. The size of the chromosomes was between 0.25 and 1.0 μm. No pronounced banding pattern was visible.     

Accumulation and exchange of parasites during adaptive radiation in an ancient lake

In the ancient Lake Baikal, Russia, amphipod crustaceans have undergone a spectacular adaptive radiation, resulting in a diverse community of species. A survey of microsporidian parasites inhabiting endemic and non-endemic amphipod host species at the margins of Lake Baikal indicates that the endemic amphipods harbour many microsporidian parasite groups associated with amphipods elsewhere in Eurasia. While these parasites may have undergone a degree of adaptive radiation within the lake, there is little evidence of host specificity. Furthermore, a lack of reciprocal monophyly indicates that exchanges of microsporidia between Baikalian and non-Baikalian hosts have occurred frequently in the past and may be ongoing. Conversely, limitations to parasite exchange between Baikalian and non-Baikalian host populations at the margins of the lake are implied by differences in parasite prevalence and lack of shared microsporidian haplotypes between the two host communities. While amphipod hosts have speciated sympatrically within Lake Baikal, the parasites appear instead to have accumulated, moving into the lake from external amphipod populations on multiple occasions to exploit the large and diverse community of endemic amphipods in Lake Baikal.     

Eocene siliceous sponges from the Ebro Basin (Catalonia, Spain)

The Eocene (Bartonian) marls of the La Guixa Member and Gurb Member, Vic Marls Formation (Ebro Basin, Catalonia, Spain), contain a very rich and diversified siliceous sponge fauna. The fauna is dominated by hexactinellids; lithistids and other demosponges are rare. It consists of 16 species representing 16 genera. Eleven new species and two new genera are proposed for these sponges: Reguantella cavernosa nov. gen. nov. sp., Regadrella concinna nov. sp. (both Hexactinellida, Lyssacinosa), Eurete clava nov. sp., Pleuroguettardia iberica nov. sp., Aphrocallistes almeriae nov. sp., Hexactinella informis nov. sp. (all Hexactinellida, Hexactinosa), Brachiolites munterensis nov. sp., Centrosia viquensis nov. sp., Callicylix eocenicus nov. sp., Rhizocheton robustus nov. sp. (all Hexactinellida, Lychniscosa), Propetrosia pristina nov. gen. nov. sp. (Demospongia, Haplosclerida). Some genera of sponges in this fauna are still extant, but, in general, the predominant ones are very close in morphology, and, without doubt, closely related to the Late Cretaceous sponges. This fauna also differs considerably, in terms of composition, from most other described faunas of Tertiary sponges from the Mediterranean region, which are dominated by lithistid sponges. Lithistid sponges are rare in this investigated assemblage, which seems most similar to an as yet undescribed Eocene fauna from Italy. There is ecological differentiation in the proportions of particular sponges in various outcrops and/or stratigraphical levels that is clearly associated with water-depth-related controlling factor(s): Munter, Tona and Sta. Cecilia represent the deepest facies, Gurb is intermediate, and St. Roc and Vespella are the most shallow. The exact bathymetric position of the sponge fauna is difficult to estimate, but it seems that 100 m (but probably 200 m and more in the case of the deepest parts) of water depth may be inferred for this facies.     

Localization of minor elements by EDS microanalysis in aragonitic sponges from the St. Cassian Beds, Italian Dolomites

The minor elements Sr, S, K, Mg, Fe, and Mn were detected by election microprobe EDS (electron dispersive spectrometer) in small regions of the skeletal tissue of the Triassic sponges Sestrostomella robusta (Zittel), Hartmanina involuta (Klipstein), Atrochetetes medius Cuif & Fischer, Ceratoporella sp., and Eudea polymorpha (Klipstein) from Alpe di Specie (St. Cassian Beds, Dolomites, Italy). Data were compared with analyses of the modern sponges Astrosclera willeyana Lister from the Mozambique Channel and Ceratoporella nicholsoni (Hickson) from the Bahamas. Sr content in Triassic sponges (mean value 9,300 ± 600 ppm) is similar to the Sr content of Recent samples (mean value 8,500 ± 1,500 ppm). This concentration of Sr shows very slight biochemical fractionation like oolitic aragonite. It is therefore possible to infer that the Triassic sea of the St. Cassian Beds had the same Sr/Ca ratio and equal aragonitic depositional conditions as those presently found in the Bahamas and the Channel of Mozambique, i.e. warm shallow waters. Generally, we did not observe a preferential distribution of minor elements with respect to structure. Only when a lower concentration in the center of spherules is observed does a preferential distribution pattern seem to exist. This could mean an initial stage of Sr leaking indicative of an incipient diagenetic process (excluding experimental errors or morphological effects). Excluding these exceptions, the Alpe di Specie spongial fauna is surely diagenetically unaltered. The Sr content shows that the micritic microstructure of Eudea polymorpha is not due to a diagenetic process either. The constant, clearly detectable occurrence of sulphur (mean value 1,000 ppm) was observed. In addition, the S content was found to be linearly correlated with the strontium content. Sulphur is probably of primary organic origin.     

The First Results of an Investigation into the Phylogenetic Diversity of Microorganisms in Southern Baikal Sediments in the Region of Subsurface Discharge of Methane Hydrates

Phylogenetic analysis of the bacterial communities in Lake Baikal bottom sediments in the region of subsurface methane hydrate discharge has been carried out using data on 16S rRNA sequences. The composition of these microbial communities is shown to be different in different horizons. Methanotrophic bacteria are found in the surface layer (0–5 cm), and uncultured bacteria constitute a great portion of this population. In deeper sediment layers (92–96 cm), a change in the microbial community occurs; specifically, a decreased homology with the known sequences is observed. The new sequences form separate clusters on a phylogenetic tree, indicating the possibly endemic nature of the bacteria revealed. Organisms related to the genus Pseudomonas constitute the main portion of the population. An archaea-related sequence was found in a horizon containing gas hydrate crystals (100–128 cm). Uncultured bacteria remain predominant.__________Translated from Mikrobiologiya, Vol. 74, No. 3, 2005, pp. 370–377.Original Russian Text Copyright © 2005 by Shubenkova, Zemskaya, Chernitsyna, Khlystov, Triboi.     

Metallothionein concentration in sponges (Spongia officinalis) as a biomarker of metal contamination

The synthesis of metallothioneins (MTs) is often induced when organisms are exposed to heavy metals in the field. They are among the major "specific" biomarkers identified to date. With a view to include MTs in biomonitoring programs, the organisms most commonly studied are bivalves. Sponges present most of the characteristics researched in bioindicators of pollution and consequently have been proposed to constitute a "Sponge Watch Program". The detection of large quantities of metals in sponges suggests the existence of detoxification systems and indeed, the presence of metallothionein-like proteins (MTLPs) has been reported in two different species of sponges. In Spongia officinalis, the present study has demonstrated the presence of compounds exhibiting most of the characteristics of MTs: cytosolic, heat-stable, with apparent molecular mass of 4 to 15 kDa and binding (at least) Ag, Cu and Zn. Specimens have been collected along the French Mediterranean coast from three sites differing by their degree of contamination. Relationships between MTLP and metal concentrations have been established. For copper, mercury and zinc, the correlations were significantly positive.     

Expression patterns and organization of the hsp70 genes correlate with thermotolerance in two congener endemic amphipod species (Eulimnogammarus cyaneus and E. verrucosus) from Lake Baikal

We studied various aspects of heat‐shock response with special emphasis on the expression of heat‐shock protein 70 (hsp70) genes at various levels in two congener species of littoral endemic amphipods (Eulimnogammarus cyaneus and E. verrucosus) from Lake Baikal which show striking differences in their vertical distribution and thermal tolerance. Although both the species studied demonstrate high constitutive levels of Hsp70, the thermotolerant E. cyaneus exhibited a 5‐fold higher basal level of Hsp70 proteins under normal physiological conditions (7 °C) and significantly lower induction of Hsp70 after temperature elevation compared with the more thermosensitive E. verrucosus. We isolated the hsp70 genes from both species and analysed their sequences. Two isoforms of the cytosolic Hsp70/Hsc70 proteins were detected in both species under normal physiological conditions and encoded by two distinct hsp/hsc70 family members. While both Hsp70 isoforms were synthesized without heat shock, only one of them was induced by temperature elevation. The observed differences in the Hsp70 expression patterns, including the dynamics of Hsp70 synthesis and threshold of induction, suggest that the increased thermotolerance in E. cyaneus (compared with E. verrucosus) is associated with a complex structural and functional rearrangement of the hsp70 gene family and favoured the involvement of Hsp70 in adaptation to fluctuating thermal conditions. This study provides insights into the molecular mechanisms underlying the thermal adaptation of Baikal amphipods and represents the first report describing the structure and function of the hsp70 genes of endemic Baikal species dwelling in thermally contrasting habitats.     

Oxygen concentration profiles in sediments of two ancient lakes: Lake Baikal (Siberia,Russia) and Lake Malawi (East Africa)

Oxygen concentration profiles have been measured, by means of with microelectrodes in sediments of Lake Baikal and Lake Malawi, along transects allowing to give a survey of two major ancient Rift lakes: Lake Baikal (Eastern Siberia) and Lake Malawi (East Africa), along depth transects in the constitutive basins of the lakes and/or of relevant depths with regard to oxygen (including including the deepest point, 1680 m, in Lake Baikal). Sediment oxygen penetration depths (SOPs) display very different patterns, depending on the lake in the two lakes. In Lake Baikal, SOPs are variable, show no significant relationship with bathymetric depth and are surprisingly deep on Akademichesky ridge (> 50.0 mm), emphasizing the distinctive feature of this region in the lake. While the Selenga river is an important source of eutrophication, the similarity of SOP-values in the Selenga shallow with those of most other sites suggests either a dilution of organic material by allochthonous matter, or a strong south-to-north transport of particles. In Lake Malawi, available oxygen is restricted to a maximum of three millimetres of the sediment, and there is a negative relationship with bathymetric depth, as a result of a steady decline of oxygen concentration with depth through the water column. Amongst the few parameters known to affect SOPs, the oxygen consumption by the sediment seems the most significant in both lakes. SOP-values furthermore confirm differences in the trophic status of Baikal and Malawi, respectively. The importance of oxygen as a factor likely to create ecological segregation for benthic organisms is discussed. Lake Malawi offers possibilities of bathymetric segregation but no vertical segregation in the sediment. In contrast, no bathymetric segregation related to oxygen is possible in Lake Baikal, but vertical segregation in the sediment is very likely. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detection and cytoplasmic localization of two different microtubule motor proteins in basal epithelial cells of freshwater sponges

Summary Epithelial sponge cells (pinacocytes) contain a set of 50 to 60 microtubules radiating from the nuclear region to the cell periphery. Vacuoles of the endocytic pathway (endosomes, lysosomes) and mitochondria move along single microtubules in both directions; moreover, the ring-like arrangement of the Golgi apparatus around the nucleus and the net-like organization of the endoplasmic reticulum in the cytoplasmic matrix are also maintained, in an energy-dependent manner, by the microtubular system. Significant changes in the velocities of retrograde and anterograde transport as well as distinct differences in the sensitivity of organelle dynamics to ATPase inhibitors and ATP analogues indicate the existence of two microtubule-based motor proteins. Ion exchange chromatography of pinacocyte homogenates resulted in the enrichment of a 97 kDa kinesin-like protein (SKLP) with the ability to cross-react with antibodies against the kinesin heavy chain. Two other polypeptides, with molecular mass of 75 and 400 kDa, apparently belonging to a cytoplasmic dynein-like protein (SDLP) could be recognized in immunoblots with antibodies against the intermediate and heavy chains of cytoplasmic dynein. In addition, three MAP-like polypeptides (SMAPLPs), with molecular mass of 280, 250 and 70 kDa, obviously related to the MAP-2 and tau-family, have been identified. Immunocytochemical studies at the light and electron microscopical level localized SKLP, SDLP, and SMAPLPs at endocytic vacuoles and mitochondria, whereas the endoplasmic reticulum has SKLP and SMAPLPs, but the Golgi apparatus only SDLP.Abbreviations AMP-PNP 5-adenylylimidodiphosphate - ATP adenosinetriphosphate - DiOC₆ (3) 3,3-dihexyloxacarbocyanine iodide - DTT 1,4-dithiothreitol - EDTA ethylenediaminetetraacetic acid - EGTA ethylene glycol-bis(-aminoethyl ether) - EHNA erythro-9-(2-hydroxy-3-nonyl)-adenine - EM electron microscope - ER endoplasmic reticulum - FPLC fast protein liquid chromatography - GA Golgi apparatus - GTP guanosinetriphosphate - HC heavy chain - HSS high-speed supernatant - IC intermediate chain - LC light chain - MAP microtubule-associated protein - MT microtubule - PIPES 1,4-piperazine-N, N-bis-(2-ethanesulfonic) acid - PMSF phenylmethylsulfonyl fluoride - SDLP sponge dynein-like protein - SDS-PAGE sodium-dodecyl-sulfate polyacrylamide gel electrophoresis - SKLP sponge kinesin-like protein - SMAPLPs sponge MAP-like proteins - UTP uridinetriphosphate     

Distribution of dissolved organic carbon in lakes of different trophic types

The distributions of dissolved organic carbon (DOC) in the warm season were elucidated in ten lakes of different trophic types in Japan, Russia, and China. DOC showed similar vertical distributions in all the lakes in summer when thermal stratification occurred. DOC in the epilimnion was higher than the value of 0.8mgCl^–1 found in the hypolimnion. In three Japanese lakes, hypolimnion DOC was negatively correlated with apparent oxygen utilization (AOU), reflecting the net oxidation of DOC using the dissolved oxygen in lake water. The DOC:O₂ ratios (0.115–0.179), calculated by the slopes of the regression lines of DOC versus AOU in hypolimnion water, were as low as those of deep-sea water, which indicates low bioavailability of lake water DOC for heterotrophic bacteria. DOC and conductivity did not correlate well except in two Japanese lakes: one showed a positive correlation and the other a negative correlation, indicating DOC loading from the inflowing rivers. Eutrophic lakes tended to have higher DOC values than meso- and oligotrophic lakes, and DOC values in the surface water negatively correlated with Secchi depths.