中国淡水三角涡虫染色体组型的研究

采用压片法对不同产地的淡水三角涡虫染色体进行研究,结果表明,湖北省武汉市珞珈山的淡水三角涡虫体细胞中有16条染色体,为二倍体（2n=2x=16m）;江苏省太湖东山岛的淡水三角涡虫体细胞中有24条染色体,为三倍体（2n=3x=24m）;贵州省遵义市凤凰山的淡水三角涡虫体细胞同时存在24条染色体和16条染色体两种分裂相,为混倍体。本文根据组型分析的结果对上述三个产地淡水三角涡虫的分类和染色体倍性进行了初步研究。另外,本研究中还发现涡虫染色体倍性的变化与涡虫生殖方式的转变以及环境温度有一定的联系。     

An assessment of biological interactions in an epilithic stream community using time-lapse cinematography

In situ time-lapse cinematography was used to record and enumerate behavioral interactions between members of an epilithic insect community in a small Michigan (U.S.A.)trout stream. 145 interactions were observed during 78 hours of filming. Most of these (98%) involved simuliid larvae. Interactions between simuliid larvae occurred at about the same frequency as interactions between simuliids and other taxa. However, interactions between simuliid larvae were less likely to lead to emigration than were interactions between blackflies and other groups. Significant short-term fluctuations of faunal density on filmed surfaces were also observed. The causes of these fluctuations appeared varied. The results of a preliminary assessment of interactions and the usefulness of this technique are discussed.     

On the origin of neoblasts in freshwater planarians (Turbellaria)

Experiments on 1) regeneration of the cave-adapted planarian, Sphalloplana zeschi, 2) induction of sexuality in an asexual strain of Dugesia japonica japonica by feeding, and 3) culture of dissociated planarian cells, show that neoblasts originate from intestinal cells, i.e. phagocytic cells and granular clubs.     

Hydrocarbon accumulation in freshwater sediments of an urban catchment

The top and bottom of two sediment cores collected from an urban receiving basin in NW London, and stormwater samples from the attendant catchment, have been analysed for their hydrocarbon content. In surface sediments, basal sediments and stormwater, total aliphatic hydrocarbon levels are 445–690 μg g⁻¹ dry wt., 43–224 μg g⁻¹ and 0.36–1.10 mg l⁻¹, respectively; and total levels of polyaromatic hydrocarbons (PAHs) are 780–1 100 μg g⁻¹, 310–640 μg g¹ and 5.83–18.21 mg l⁻¹, respectively. Biodegradation of aliphatics is assessed by phytane:n-C₁₈ and pristane: n-C₁₇ ratios. Hydrocarbon sources are determined from phytane: pristane ratios, odd: even carbon chain length ratios, the presence of an unresolved complex mixture, and by comparison of the amount of methyl-substituted PAH s with that of the parent compounds. Comparison of total levels between surface and basal sediments shows a 1 to 3 fold increase in total PAHs and a 3 to 10 fold increase in aliphatic hydrocarbons over a 120 year period.     

Impact of seasonal changes in stream metabolism on nitrate concentrations in an urban stream

Nitrate (NO₃ ^?) dynamics in urban streams differ from many natural streams due to stormwater runoff, sewage inputs, decreased groundwater discharge, often limited hyporheic exchange, increased primary productivity, and limited carbon input. We investigated NO₃ ^? dynamics in a first-order urban stream in Syracuse, NY, which has urbanized headwaters and a geomorphologically natural downstream section. Twice-monthly water sampling, NO₃ ^? injection tests, NO₃ ^? isotopic analysis, filamentous algae mat density, and riparian shading were used to identify processes regulating NO₃ ^? dynamics in the stream over a 12-month period. The urban headwater reach had low NO₃ ^? (0.006–0.2 mg N/L) in the spring through fall, with a minimum uptake length of 900 m, no canopy cover, and high algae mat density. The downstream natural reach (100% canopy cover during the summer and low algae mat density) had nitrate concentrations between 0.6 and 1.2 mg N/L from winter to summer, which decreased during autumn leaf-off. In the urban reach, autotrophic uptake by filamentous green algae is a major NO₃ ^? sink in summer. In the natural reach, the addition of organic matter to the stream at leaf-off led to a decrease in NO₃ ^? concentration followed by an increase in NO₃ ^? concentration in winter as gross primary productivity decreased. This study shows that the balance between autotrophy and heterotrophy in urban streams is variable and depends on an interplay of drivers such as temperature, light, and carbon inputs that are mediated by the riparian ecosystem.     

Growth and survival of peritrich ciliates in an urban stream

Summary A computerized system was devised to trace the attachment, growth and disappearance of peritrich ciliates in an urban river. By tracing the development of each Carchesium polypinum colony in the river, it was possible to estimate the actual growth rate of this species without considering the effect of immigration. The survival and colonization rates of the colonies and individuals of solitary species could also be estimated. C. polypinum showed high growth rates (r=1.370 day^-1, doubling time 12.14 h). The number of daily colonizers also increased at a high rate, and the combination of growth and colonization caused very high population increase rates at the area level. Because of its low survivorship, the rate of Vorticella microstoma increase was much lower than previously reported. The survival of solitary species and small colonies was lower than with large colonies, and fewer new colonizers survived with the development of the attached microbial community.     

Evaluation of denitrification in an urban stream receiving wastewater effluent

Urban streams often contain elevated concentrations of nitrogen (N) which can be amplified in systems receiving effluent from wastewater treatment plants (WWTP). In this study, we evaluated the importance of denitrification in a stream draining urban Greensboro, NC, USA, using two approaches: (1) natural abundance of ¹⁵N–NO₃⁻ in conjunction with background NO₃⁻–N concentrations along a 7 km transect downstream of a WWTP; and (2) C₂H₂ block experiments at three sites and at three habitat types within each site. Overall lack of a longitudinal pattern of δ¹⁵N–NO₃⁻ and NO₃⁻–N, combined with high concentrations of NO₃⁻–N suggested that other factors were controlling NO₃⁻–N flux in the study transect. However, denitrification did appear to be significant along one portion of the transect. C₂H₂ block experiments showed that denitrification rates were much higher downstream of the WWTP compared to upstream, and showed that denitrification rates were highest in erosional and depositional areas downstream of the WWTP and in erosional areas upstream of the plant. Thus, the combination of the two methods for evaluating denitrification provided more insight into the spatial dynamics of denitrification activity than either approach alone. Denitrification appeared to be a significant sink for NO₃⁻–N upstream of the WWTP, but not downstream. Approximately 46% of the total NO₃⁻–N load was removed via denitrification in the upstream, urban section of the stream, while only 2.3% of NO₃⁻–N was lost downstream of the plant. This result suggests that controlling NO₃⁻–N loading from the plant could result in considerable improvement of downstream water quality.     

Habitat segregation among freshwater shrimp species in an Amazonian rainforest stream system

1. Resource partitioning is a stabilising mechanism known to maintain species diversity in a variety of environments. Assemblages of stream shrimp species are structured by habitat features and predation. Therefore, segregation along habitat dimensions could facilitate coexistence among species in shrimp assemblages even when segregation is a result of predation pressure by fish species. These ecological interactions take place on a background modulated by biogeographic features, such as connectivity among drainages. However, these generalisations are mainly based on studies undertaken in temperate regions.
2. We investigated whether abundances of rainforest shrimp species are related to habitat dimensions, and whether habitat–abundance relationships might be mediated through fish-assemblage structure and the effect of drainages on connectivity.
3. We detected effects of habitat variation on densities of shrimp species, but the magnitudes of the effects were larger for some species than others. Fish-assemblage composition also affected shrimp densities. Two of the three species of shrimp showed some degree of habitat specialisation, but only along current-velocity, depth, and pH gradients. Habitat segregation among species occurred along the current-velocity and pH gradients. Relationships between density and environmental gradients differed between catchments for only one species and only along the pH gradient.
4. Our findings provide evidence that rainforest-stream shrimp species respond differently to environmental gradients and this could facilitate coexistence among species. However, interactions with fish seem to have a stronger effect on species densities, and consequently species segregation, than direct effects of the environmental gradients, resulting in apparent competition for these resources.

     

中国淡水涡虫RAPD分析条件的优化（简报）

涡虫是动物界最早出现两侧对称、三胚层、营自由生活的扁形动物,也是由水生向陆生过渡的重要类群,因而在动物系统演化中占有重要地位。由于涡虫再生能力极强,因此成为研究细胞分化与去分化分子机理的理想材料,近百年来一直是国际动物学界热衷探索的研究领域之一。然而遗憾的是,我国动物学界从事涡虫研究者甚少,属于基础十分薄弱的     

Influence of urban tributaries on freshwater mussel populations in a biologically diverse piedmont (USA) stream

We investigated the distribution patterns of senescent and green leaf litter patches on a streambed to evaluate the hypothesis that the different immersion times of senescent leaves in long-term benthic storage and newly retained green leaves affect streambed distribution patterns in summer (June, July, and August). We counted all the leaf litter patches in the streambed of the study reach, comparing the physical condition of patches and classifying the trapping obstacles associated with each patch type. The distribution patterns of senescent and green leaf litter patches differed. Green leaf litter patches were more numerous at every sampling date, with most trapped by cobbles, whereas senescent leaf litter patches were retained by twig obstacles, backwaters, and cobbles. In June and July, senescent leaf litter patches were located in significantly deeper stream areas than were green leaf litter patches. The distribution of senescent leaves would be primarily determined during spring snowmelt-driven floods. We speculate that senescent leaves were originally located at the edges of pools in the main flow pathway of the channel, which overflowed in the floods. We conducted flume experiments to clarify the transport characteristics of senescent and green painted maple and manchurian alder leaves in the water column. Our hypothesis was that the transport characteristics of each leaf type differ when they first enter the water, because of differing leaf properties. The flume experiments showed that duration of surface flotation differed for senescent and green leaves and for the two tree species. These differences in the duration of leaves on the streambed and in the floating time of green leaves of different trees ensure varied food resources for macroinvertebrates in various physical conditions. Handling editor: B. Oertli     

Molecular phylogeny of land and freshwater planarians (Tricladida, Platyhelminthes): from freshwater to land and back

The suborder Tricladida (phylum Platyhelminthes) comprises the well-known free-living flatworms, taxonomically grouped into three infraorders according to their ecology: Maricola (marine planarians), Paludicola (freshwater planarians), and Terricola (land planarians). Molecular analyses have demonstrated that the Paludicola are paraphyletic, the Terricola being the sister group of one of the three paludicolan families, the Dugesiidae. However, neither 18S rDNA nor COI based trees have been able to resolve the relationships among species of Terricola and Dugesiidae, particularly the monophyly of Terricola. Here, we present new molecular data including sequences of nuclear genes (18S rDNA, 28S rDNA) and a mitochondrial gene (COI) of a wider sample of dugesiid and terricolan species. The new sequences have been analyzed, together with those previously obtained, in independent and concatenated analyses using maximum likelihood and bayesian methods. The results show that, although some parts of the trees remain poorly resolved, they support a monophyletic origin for Terricola followed by a likely return of some species to freshwater habitats. Relationships within the monophyletic group of Dugesiidae are clearly resolved, and relationships among some terricolan subfamilies are also clearly established and point to the need for a thorough revision of Terricola taxonomy.     

The power of regeneration and the stem-cell kingdom: freshwater planarians (Platyhelminthes)

The great powers of regeneration shown by freshwater planarians, capable of regenerating a complete organism from any tiny body fragment, have attracted the interest of scientists throughout history. In 1814, Dalyell concluded that planarians could "almost be called immortal under the edge of the knife". Equally impressive is the developmental plasticity of these platyhelminthes, including continuous growth and fission (asexual reproduction) in well-fed organisms, and shrinkage (degrowth) during prolonged starvation. The source of their morphological plasticity and regenerative capability is a stable population of totipotent stem cells--"neoblasts"; this is the only cell type in the adult that has mitotic activity and differentiates into all cell types. This cellular feature is unique to planarians in the Bilateria clade. Over the last fifteen years, molecular studies have begun to reveal the role of developmental genes in regeneration, although it would be premature to propose a molecular model for planarian regeneration. Genomic and proteomic data are essential in answering some of the fundamental questions concerning this remarkable morphological plasticity. Such information should also pave the way to understanding the genetic pathways associated with metazoan somatic stem-cell regulation and pattern formation.     

Evaluation of water quality of an urban stream in southeastern Brazil using Chironomidae larvae (Insecta: Diptera)

In order to estimate the water quality of S?o Pedro stream, through distribution and composition of Chironomidae larvae present in the sediment four sampling sites were selected. In each sampling site, three sediment samples were collected within a period of twelve months using the Petersen (0.0189 m2) and the van Veen (0.0518 m2) dredges. Samples were washed through a sieve with a 0.21 mm mesh and the collected organisms were sorted in transparent trays, with a light shine being reflected into the tray. The sites located in the greatest urban mesh showed high densities of the genus Chironomus and lower values for diversity, uniformity and taxa richness, in relation to sites located in a less urbanized area. A significant difference in density of Chironomidae larvae (p = 0.02; H = 5.89) was observed between the sites without domestic sewage effluents (site I) and those with the input of the effluents (sites II, III and IV). The Chironomidae larvae composition and the physical and chemical parameters were effective as indicators of the environmental alterations in S?o Pedro stream.     

Environmental heterogeneity limits the local dominance of an invasive freshwater crustacean

The impacts of an exotic species may vary along environmental gradients. We tested the hypothesis that site-specific heterogeneity in the physico–chemical environment alters the dominance of two competing amphipods: Gammarus fasciatus, the dominant native species in the upper St. Lawrence River, and Echinogammarus ischnus, a euryhaline Ponto-Caspian species that invaded the river in the late 1990s. E. ischnus has replaced G. fasciatus as the dominant amphipod at some sites, while remaining inferior at other sites—even several years after invasion. We tested the effect of water chemistry (conductivity) on the outcome of interactions between these two species in the laboratory and in the river in 2006 and 2007. Field experiments involved transplanting both species to different sites along a gradient of conductivity within the river, whereas the laboratory experiments examined interspecific predation in water collected from these sites. The laboratory experiments revealed that these species are mutual predators and their rate of predation on each other varies with conductivity; E. ischnus is the dominant predator at higher conductivity, while G. fasciatus dominates at lower conductivity. The field experiments showed interannual variation, but supported the lab results at high conductivity in 2006 and at low conductivity in 2007. E. ischnus was more sensitive than G. fasciatus to variation in conductivity, which apparently mediates this invader’s ability to replace or dominate the native species in a heterogeneous environment.     

Quantitative assessment of the genotoxicity of fecapentaenes

Fecapentaenes are a group of fecal mutagens of microbial origin isolated from human stools. Fecapentaene-12 (F-12) and fecapentaene-14 (F-14), differing only in two carbon atoms in the side chain, are glyceryl ethers with a highly reactive chromophoric aliphatic side chain incorporating a conjugated pentaene moiety. Although these compounds are known for their genotoxicity, no test systems have been developed to precisely assess their relative genotoxicity. In this study F-12 and F-14 were assayed for their genotoxicity using the SOS Chromotest in which the induction of beta-galactosidase in E. coli PQ37 was used as a quantitative measure of biological activity. The activity obtained with F-12 and F-14 was compared with that of 4-nitroquinoline oxide (4-NQO) as the reference standard of a direct acting mutagen. While F-14 was almost as active as 4-NQO, F-12 was only about 25% as active as F-14, the higher analog.