Testate amoebae (Protozoa) in lakes of the Qinghai-Tibet Plateau: Biodiversity, community structures, and protozoic biosilicification in relation to environmental properties and climate warming.

The Qinghai-Tibet Plateau (QTP) is characterized by a vast number of frozen and unfrozen freshwater reservoirs, which is why it is also called "the third pole" of the Earth or "Asian Water Tower". We analyzed testate amoeba (TA) biodiversity and corresponding protozoic biosilicification in lake sediments of the QTP in relation to environmental properties (freshwater conditions, elevation, and climate). As TA are known as excellent bio-indicators, our results allowed us to derive conclusions about the influence of climate warming on TA communities and microbial biogeochemical silicon (Si) cycling. We found a total of 113 TA taxa including some rare and one unknown species in the analyzed lake sediments of the QTP highlighting the potential of this remote region for TA biodiversity. >1/3 of the identified TA taxa were relatively small (<30 µm) reflecting the relatively harsh environmental conditions in the examined lakes. TA communities were strongly affected by physico-chemical properties of the lakes, especially water temperature and pH, but also elevation and climate conditions (temperature, precipitation). Our study reveals climate-related changes in TA biodiversity with consequences for protozoic biosilicification. As the warming trend in the QTP is two to three times faster compared to the global average, our results provide not only deeper insights into the relations between TA biodiversity and environmental properties, but also predictions of future developments in other regions of the world. Moreover, our results provide fundamental data for paleolimnological reconstructions. Thus, examining the QTP is helpful to understand microbial biogeochemical Si cycling in the past, present, and future.

Benthic macroinvertebrate assemblages in relation to high ammonia loading: A 5-year fertilization experiment in 5 subtropical ponds.

Nitrogen pollution, especially ammonia, and its impacts on aquatic ecosystems are always hot topics worldwide. Evaluating the toxicity effect of ammonia on aquatic organisms is the essential basis for nitrogen management. Benthic macroinvertebrates are widely used to evaluate ammonia toxicity based on acute and chronic lab tests. In comparison, responses of macroinvertebrates under field and controlled conditions were rarely studied. To explore the effect of ammonia on macroinvertebrate assemblages and the underlying mechanisms under field conditions, a 5-year fertilization experiment was conducted in 5 quasi-natural ponds located in the Yangtze River floodplain. One control (TN0, no artificial ammonia loading) and four treatments (TN2, TN10, TN20, TN100; ordered by artificial ammonia loading from low to high) were set. The results showed that (1) species number of macroinvertebrates differed little among the ponds, while total density and biomass were positively correlated with unionized ammonia concentration (NH3), indicating that increased ammonia loading had no adverse impact on macroinvertebrate abundance; (2) all ponds were dominated by gathering collectors and the biomass was higher in the ponds with higher ammonia loading resulting from the more phytoplankton promoted by ammonia loading and improved internal phosphorus release; (3) the biomass of predators also increased with the increasing NH3 which may be due to the bottom-up effect through their prey; (4) some species, such as Limnodrilus hoffmeisteri, survived and were dominant species in the ponds with higher NH3 compared with 96 h median lethal concentration from acute lab test. The results suggested that higher ammonia loading increased macroinvertebrate abundance, mainly contributed by gathering collectors and predators. Unlike previous acute and chronic lab tests, macroinvertebrates showed extremely high tolerance to NH3 in field conditions. This study supported that ammonia toxicity to aquatic organisms was scale-dependent and should be evaluated at multiple scales.

Short-term responses of macroinvertebrate assemblages to the "ten-year fishing ban" in the largest highland lake of the Yangtze basin.

The rapid decline of freshwater biodiversity caused by overfishing has led to the implementation of a series of conservation measures, including fishing bans. However, existing studies have mostly focused on the effects of fishing bans on economically important species, while impacts on freshwater macroinvertebrates in lake ecosystems have been rarely studied. This study used a before-and-after methodology to determine the short-term effects of the "ten-year fishing ban" on the macroinvertebrates of the Dianchi Lake, the largest highland freshwater lake in the upper Yangtze basin, between 2015 and 2022. Following the fishing ban, the overall macroinvertebrate species richness (median [interquartile]) across sites increased from 4 [2-6] to 5 [4-7]. The total density increased from 128 [80-272] to 212 [140-325] n/m2. The median biomass increased from 0.18 [0.08-0.41] to 0.51 [0.26-2.36] g/m2. In particular, the Chironomidae density in the offshore sites increased from 16.00 [0.00-32.00] to 33.30 [16.00-48.00] n/m2, and the biomass increased from 0.03 [0.00-0.09] to 0.16 [0.07-0.22] g/m2. Within the inshore sites, the aquatic insect density increased from 4 [1.33-15.33] to 56 [22.00-86.67] n/m2. The Malacostraca density increased from 34.67 [11.67-95.33] to 110 [53.33-223.33] n/m2, and the biomass increased from 0.43 [0.11-1.00] to 1.48 [0.50-2.00] g/m2. Two endangered Margarya species were rediscovered at multiple sites compared to the pre-fishing ban period. A significant change in macroinvertebrate community structure across the lake was observed, which can be largely attributed to the fishing ban. The immediate increase in species richness, density, and biomass of most macroinvertebrate species suggests a combination of effects from both reduced exploitation pressure and lessened disturbances on lake habitats. The findings indicate that the fishing ban is beneficial for the recovery of most macroinvertebrate species in freshwater lakes.

Integrative taxonomy of a new species of Rhyacodrilus (Annelida: Clitellata: Rhyacodrilinae) from Tibet Plateau rivers, with a preliminary assessment of its phylogenetic position.

A new Qinghai-Tibet Plateau species, Rhyacodrilus tanggulaensis Jiang & Cui sp. nov. (Annelida, Clitellata, Naididae, Rhyacodrilinae), is described, and its phylogenetic relationships within the genus is assessed on the basis of both mitochondrial (16S rDNA, COⅠ gene) and nuclear (ITS2) markers. Data from 32 species of Naididae, representing 7 subfamilies and 25 genera are used. Ten species were chosen as outgroup taxa. The molecular data were analyzed by Bayesian inference. The new species is distinguished from other species of Rhyacodrilus by the following combination of characters: dorsal and ventral chaetae with distal tooth 2-3 times longer than proximal, spermathecal and penial chaetae present, atria long and tubular, atrial duct conspicuous. The analyses of the combined molecular data corroborate the close relationship between Naidinae and the rhyacodriline genera Rhyacodrilus, Monopylephorus, and Ainudrilus, and show that the new species is more closely related to R. falciformis, R pigueti, R. okamikae and R. subterraneus, than to R. sinicus, another Chinese species, R. hiemalis and R. coccineus.

A Simple Index of Lake Ecosystem Health Based on Species-Area Models of Macrobenthos.

An effective biological index should meet two criteria: (1) the selected parameters have clear relationships with ecosystem health and can be measured simply by standard methods and (2) reference conditions can be defined objectively and simply. Species richness is a widely used estimate of ecosystem condition, although it is increased by nutrient enrichment, a common disturbance. Based on macrobenthos data from 91 shallow Yangtze lakes disconnected from the mainstem, we constructed an observed species (SO)-area (A) model to predict expected species richness (SE), and then developed an observed to expected index (O/E-SA) by calculating the SO/SE ratio. We then compared O/E-SA with three other commonly used indices regarding their ability to discriminate cultivated and urban lakes: (1) River Invertebrate Prediction and Classification System (RIVPACS; O/E-RF), (2) Benthic Index of Biotic Integrity (B-IBI), and (3) Average Score Per Taxon (ASPT). O/E-SA showed significant positive linear relationships with O/E-RF, B-IBI and ASPT. Quantile regressions showed that O/E-SA and O/E-RF had hump-shape relationships with most eutrophication metrics, whereas B-IBI and ASPT had no obvious relationships. Only O/E-SA, O/E50 and B-IBI significantly discriminated cultivated from urban lakes. O/E-SA had comparable or higher performance with O/E-RF, B-IBI and ASPT, but was much simpler. Therefore, O/E-SA is a simple and reliable index for lake ecosystem health bioassessment. Finally, a framework was proposed for integrated biological assessment of Yangtze-disconnected lakes.

Land conversion induced by urbanization leads to taxonomic and functional homogenization of a river macroinvertebrate metacommunity.

Conversion of forests to urban land-use in the processes of urbanization is one of the major causes of biotic homogenization (i.e., decline in beta diversity) in freshwater ecosystems, threating ecosystem functioning and services. However, empirical studies exploring urban land-use shaping patterns of taxonomic and functional beta diversities and their components in subtropical urban rivers are limited. Here, by leveraging data for 43 sampling sites from urban and forest rivers in Shenzhen, a megacity showing rapid urbanization, we determined the spatio-temporal dynamics and associated drivers of taxonomic and functional beta diversities of river macroinvertebrates. Our results showed that, from the forest to urban rivers, taxonomic beta diversity (wet: 32.9%; dry: 17.1%) declined more significantly than functional beta diversity (wet: 17.4%; dry: 9.5%) in different seasons. We further found that these compositional changes were largely driven by decreased roles of species/traits replacement. Although replacement was also dominant for taxonomic beta diversity (60.4%-68.4%) in two sets of rivers, richness difference contributed more to functional beta diversity in the urban river (52.6%-60.5%). Both deterministic and stochastic processes simultaneously affected beta diversity, with stochastic processes being more important in the urban (3.0-19.0%) than forest rivers (0.0%-3.0%). Besides, db-RDA and variation partitioning results showed that local-scale environmental variables explained considerably large fractions of variation in beta diversity. We hence recommended that biodiversity conservation should focus on improving and restoring local environmental conditions. Despite no significant seasonal differences in beta diversity were detected in this study, we found that the roles of deterministic (i.e., local-scale and land-use variables) and stochastic processes varied considerately across seasons. This result highlights the viewpoint that urban river biodiversity monitoring should go beyond one-season snapshot surveys. As the ongoing trend of urbanization in developing countries, the findings of this study are relevant in guiding urban river environmental monitoring, biodiversity conservation and land-use planning.

DNA barcoding of Naididae (Annelida, Oligochaeta), based on cytochrome C oxidase gene and ITS2 region in China.

Exploring the effectiveness of DNA barcoding in species identification is a prerequisite for biodiversity conservation and environmental monitoring. Aquatic oligochaetes could serve as excellent indicators in aquatic monitoring programmes. However, few studies have examined the effectiveness of DNA barcoding in these specific organisms. The mitochondrial cytochrome C oxidase (COI) gene of 83 specimens belonging to 40 species of 18 genera were sequenced in this study. The results showed that there was a barcode gap between species of Naididae and the intraspecific genetic distances of each species were smaller than interspecific genetic distances. The classification results of ABGD (Automatic Barcode Gap Discovery) were consistent with those of morphological identification, except for Tubifextubifex and Lumbriculusvariegatus. All species were successfully distinguished in the phylogenetic tree, based on the ITS2 region, which was coincident with the morphological result. Our results provided evidence that DNA barcoding can be used as an effective and convenient tool for species identification of the family Naididae and even for other aquatic oligochaetes.

Molecular taxonomy and description of a new species of Limnodrilus (Naididae, Clitellata, Annelida) in China.

The freshwater annelid worm genus Limnodrilus, including the widely distributed L. claparedianus Ratzel, 1868, is common in Chinese freshwater ecosystems. One species, previously recognized as morphologically intermediate between L. claparedianus and the North American taxon L. cervix Brinkhurst, 1963, is here described as a new species, L. paraclaparedianus Zhou Cui n. sp., using both molecular and traditional taxonomy. Comparisons of sequences of the Cytochrome Oxidase subunit I (COI) mtDNA in a sample of Limnodrilus species showed that the distances between species were generally higher than the divergences within them. Phylogenetic analysis of COI as well as 16S mtDNA and Internal Transcribed Spacer 2 (ITS2) nDNA confirmed that the new species is an independent lineage. Moreover, morphological differences in the prostomium, characteristics of the chaetae and internal genitalia support the separation of the species.

Analyzing the Response Behavior of Lumbriculus variegatus (Oligochaeta: Lumbriculidae) to Different Concentrations of Copper Sulfate Based on Line Body Shape Detection and a Recurrent Self-Organizing Map.

Point detection (e.g., the centroid of the body) of species has been conducted in numerous studies. However, line detection (i.e., the line body shape) of elongated species has rarely been investigated under stressful conditions. We analyzed the line movements of an Oligochaeta Lumbriculus variegatus in response to treatments with a toxic chemical, copper sulfate, at low concentrations (0.01 mg/L and 0.1 mg/L). The automatic line-tracking system was devised to identify the movement of body segments (body length) and the movements of segments (i.e., the speed and angles between segments) were recorded before and after treatment. Total body length was shortened from 31.22 (±5.18) mm to 20.91 (±4.65) mm after the 0.1 mg/L treatment. The Shannon entropy index decreased from 0.44 (±0.1) to 0.28 (±0.08) after treatment. On the other hand, the body and movement segments did not significantly change after the 0.01 mg/L treatment. Sequential movements of test organisms were further analyzed with a recurrent self-organizing map (RSOM) to determine the pattern of time-series line movements. The RSOM made it feasible to classify sequential behaviors of indicator organisms and identify various continuous body movements under stressful conditions.

Records of Naididae and Lumbriculidae (Clitellata) from Tibet, China, with description of a new species of Nais.

The Tibetan Plateau is considered to have a unique fauna of fish and invertebrates. However, little taxonomic work has been conducted on the aquatic Oligochaeta of Tibet, China. Based on the surveys of rivers and lakes in this region between 2010 and 2011, we recorded 25 species of oligochaetes belonging to 2 families and 15 genera. This paper provides an overview of the species composition of different waterbodies, the description of one new species, Nais longidentata sp. n., and re-descriptions of four previously described species. Hitherto, 30 species of aquatic oligochaetes have been recorded from Tibet. The oligochaete fauna is similar to that of the Holarctic, but has several endemic elements.

Two species of Naididae (Annelida, Clitellata) from southern Tibet, China.

One new species of Naidinae (Oligochaeta, Naididae), Naisbadia sp. n. and one new record species from China, Tubifexmontanus Kowalewski, 1919 (Tubificinae) are found in southern Tibet. The new species is distinguished from congeners by its large area of reddish brown pigment in the anterior segments I-VIII, serrate hairs, pectinate needles with 1-2 intermediate teeth, ventral chaetae partly with 1-2 fine intermediate teeth and wave-like movements. The new material of the species Tubifexmontanus differs slightly from the previous descriptions by its vas deferens entering atrium subapically, wide ental end of penial sheath and smooth hair chaetae.

Three new species of Potamothrix (Oligochaeta, Naididae, Tubificinae) from Fuxian Lake, the deepest lake of Yunnan Province, Southwest China.

Three new species of Potamothrix Vejdovský & Mrázek, 1902 (Oligochaeta: Tubificinae), Potamothrix praeprostatussp. n., Potamothrix paramoldaviensissp. n. and Potamothrix parabedotisp. n., are reported from Fuxian Lake of Yunnan Province, Southwest China. Potamothrix praeprostatusdiffers from its allies by its prostate glands joining atria in its proximal to middle portion, and spermathecal chaetae. Potamothrix paramoldaviensis is distinguishable from its allies by having penial chaeta but no penes, and differs from Potamothrix moldaviensisby its homogenous atrium. Potamothrix parabedoti is distinctive in the position of its reproductive organs, and differs from Potamothrix bedoti by its homogenous atrium. Hitherto, 34 freshwater oligochaete species have been recorded in Yunnan Province, including nine endemic species from the plateau lakes.

Limnodrilus simplex sp. nov. (Oligochaeta: Naididae: Tubificinae) from Changjiang River, China.

Limnodrilus simplex sp. nov. (Oligochaeta: Naididae: Tubificinae) is described based on a single specimen from the mainstream of the Changjiang River near Anqing City, Anhui Province, China. The new species is assigned to Limnodrilus by the presence of long vasa deferentia, spindle-shaped atria with long ejaculatory ducts, large prostate glands, and thick cylindrical penial sheaths. It differs from its congeners in having simple-pointed chaetae and cuticularized penial sheaths without hoods. Limnodrilus simplex is closer to L. paramblysetus and L. amblysetus in possessing penial sheaths with relatively low length/maximum width ratio.

Potamothrix scleropenis sp. nov. (Oligochaeta: Tubificidae) from Fuxian Lake, the deepest lake in southwest China.

Potamothrix scleropenis sp. nov. (Tubificidae: Tubificinae) is described from the profundal zone (74 m) of Fuxian Lake, the deepest lake (up to 155 m) on the Yunnan-Guizhou Plateau in China. The new species is assigned to Potamothrix because of its short vasa deferentia and its tubular atria without ejaculatory ducts and prostate glands. It differs from congeners by its cuticularized penis sheaths; bifurcated, strongly curved spermathecal chaetae; bifurcated lower prongs of bifids; and feathered hairs. P. scleropenis appears closely related to P. cekanovskajae Finogenova, 1972 and P. tudoranceai Sporka, 1994, since all the three species have homogeneous atria without prostate glands.