Testate amoebae community structure in the moss biotopes of streams

The specific composition and community structure of testate amoebae in the moss biotopes of streams were studied in the Sura River basin (Middle Volga region). Twenty-nine species and forms were identified. The eurybiont species Trinema enchelys, Euglypha ciliata glabra, Centropyxis aerophila, Tracheleuglypha dentata, Crythion dubium, Centropyxis cassis, Trinema complanatum, and Trinema lineare are dominant. The species richness varies from 2 to 11 species per sample, the abundance is 100 to 4000 ind./g of absolutely dry moss. The degree of forest covering in the basin, hydrochemical peculiarities (the amount of biogenic elements and water hardness) of streams, the size of streams, and environmental contamination are possible factors that determine the specific character of the composition and structure of testate amoebae communities.     

Testate amoebae community pattern in different types of boundary structures at the water-land contact zone

The patterns of changes in the species richness, abundance, species composition, and species structure of the testate amoebae community along six different types of water-land boundaries in the Medveditsa River (Don river Basin) were studied, namely, a new boundary, terrigenous and reogeneous edges, reogeneous and terrigenous hemiecotones, and the full ecotone. The testate amoebae communities are divided into terrestrial and aquatic variants for all types of boundaries. Hydrophilic species of the genera Arcella, Diffugia, Cyphoderia, and Pseudodifflugia dominate in the aquatic types of communities while pedobiont and eurybiont groups from the genera Centropyxis, Euglypha, Plagiopyxis, and Trinema are characteristic of the terrestrial communities. A decrease in the abundance and species richness of testate amoebae in the boundary zones was detected.     

Plant functional group diversity promotes soil protist diversity

We tested whether effects of plant diversity can propagate through food webs, down to heterotrophic protists not linked directly to plants. To this end we synthesised grassland ecosystems with varying numbers of plant functional groups (FGN) and assessed corresponding changes in testate amoebae communities. The number of plant species was kept constant. When FGN was increased from 1 to 3, species number and total community density of live testate amoebae were enhanced according to a linear and a saturating function, respectively. From FGN 1 to 2, the appearance of new testate amoebae species did not affect the presence of the resident species, whereas, from FGN 2 to 3 about one quarter of the resident testate amoebae species was replaced, without altering the total species number. Overall, density by species increased, while evenness of the testate amoebae community was not affected by FGN; although Trinema lineare, one of the most common species, became more abundant. The observed relationship between plant functional group diversity and testate amoebae diversity could shed new light on the biogeographical distribution patterns of protists.     

The Impact of Simulated Sulfate Deposition on Peatland Testate Amoebae

Peatlands subjected to sulfate deposition have been shown to produce less methane, believed to be due to competitive exclusion of methanogenic archaea by sulfate-reducing bacteria. Here, we address whether sulfate deposition produces impacts on a higher microbial group, the testate amoebae. Sodium sulfate was applied to experimental plots on a Scottish peatland and samples extracted after a period of more than 10 years. Impacts on testate amoebae were tested using redundancy analysis and Mann–Whitney tests. Results showed statistically significant impacts on amoebae communities particularly noted by decreased abundance of Trinema lineare, Corythion dubium, and Euglypha rotunda. As the species most reduced in abundance are all small bacterivores we suggest that our results support the hypothesis of a shift in dominant prokaryotes, although other explanations are possible. Our results demonstrate the sensitivity of peatland microbial communities to sulfate deposition and suggest sulfate may be a potentially important secondary control on testate amoebae communities.     

SSU rRNA reveals a sequential increase in shell complexity among the euglyphid testate amoebae (Rhizaria: Euglyphida)

The existing data on the molecular phylogeny of filose testate amoebae from order Euglyphida has revealed contradictions between traditional morphological classification and SSU rRNA phylogeny and, moreover, the position of several important genera remained unknown. We therefore carried out a study aiming to fill several important gaps and better understand the relationships among the main euglyphid testate amoebae and the evolutionary steps that led to the present diversity at a higher level. We obtained new SSU rRNA sequences from five genera and seven species. This new phylogeny obtained shows that (1) the clade formed by species of genera Assulina and Placocista branches unambiguously at the base of the subclade of Euglyphida comprising all members of the family Trinematidae and genus Euglypha, (2) family Trinematidae (Trachelocorythion, Trinema, and Corythion) branches as a sister group to genus Euglypha, (3) three newly sequenced Euglypha species (E. cf. ciliata, E. penardi, and E. compressa) form a new clade within the genus. Since our results show that Assulina and Placocista do not belong to the Euglyphidae (unless the Trinematidae are also included in this family), we propose the creation of a new family named Assulinidae. Consequently, we give a family status to the genera Euglypha and (tentatively) Scutiglypha, which become the new family Euglyphidae. The evolutionary pattern suggested by SSU rRNA phylogeny shows a clear tendency towards increasing morphological complexity of the shell characterised by changes in the symmetry (migration of the aperture to a ventral position and/or compression of the shell) and the appearance of specialised scales at the aperture (in families Trinematidae and Euglyphidae).     

Species composition and structure of testate amoebae community in a sphagnum bog at the initial stage of its formation

A total of 42 species and forms have been revealed in the testate amoebae community of a transitional bog at the initial stage of transformation into a typical sphagnum bog. A distinctive features of its species composition is dominance of widespread species Assulina muscorum, Arcella arenaria, Phryganella hemisphaerica, and Euglypha laevis in the absence of common sphagnobionts of the genera Nebela, Hyalosphenia, and Heleopera. Vertical heterogeneity of the community structure is weakly manifested, since dominant species are abundant in all horizons. The highest species richness is characteristic of the marginal community formed at the boundary between a sphagnum quagmire and a reed grass-dominated fen.     

The moss dwelling testacean fauna of Île de la Possession

An ecological study of the moss dwelling testacean fauna (Protozoa, Rhizopoda) on Île de la Possession (Crozet Archipelago, sub-Antarctica) revealed 83 taxa, belonging to 21 genera. The moss flora was dominated by cosmopolitan and ubiquitous taxa, such as Trinema lineare, T. enchelys, Euglypha laevis and E. rotunda. A cluster analysis and a correspondence analysis identified three communities: (1) a Corythion dubium assemblage found in a drier, slightly acidic terrestrial moss vegetation, (2) the Arcella arenaria, and (3) the Difflugiella crenulata assemblages, both characteristic of wetter, circumneutral habitats. The latter typified submerged mosses growing in running water, while the A. arenaria assemblage seemed to prefer mosses in standing waterbodies. Moisture conditions appeared to play a key role in determining the distribution pattern of testacean communities, while pH was only a secondary factor. A logistic regression emphasised the effect of the habitat type in controlling the variance in testacean assemblages. Moreover, the close relationship between bryophyte species and habitat type had a significant influence on the distribution pattern of the testate amoebae. Weighted averaging and calibration were used to estimate moisture optima and tolerances of the testate amoebae.     

Environmental factors influencing soil testate amoebae in herbaceous and shrubby vegetation along an altitudinal gradient in subarctic tundra (Abisko,Sweden)

Shifts in community composition of soil protozoa in response to climate change may substantially influence microbial activity and thereby decomposition processes. However, effects of climate and vegetation on soil protozoa remain poorly understood. We studied the distribution of soil testate amoebae in herbaceous and shrubby vegetation along an altitudinal gradient (from below the treeline at 500 m to the mid-alpine region at 900 m a.s.l.) in subarctic tundra. To explain patterns in abundance, species diversity and assemblage composition of testate amoebae, a data set of microclimate and soil chemical characteristics was collected. Both elevation and vegetation influenced the assemblage composition of testate amoebae. The variation was regulated by interactive effects of summer soil moisture, winter soil temperature, soil pH and nitrate ion concentrations. Besides, soil moisture regulated non-linear patterns in species richness across the gradient. This is the first study showing the effects of winter soil temperatures on species composition of soil protozoa. The effects could be explained by specific adaptations of testate amoebae such as frost-resistant cysts allowing them to survive low winter temperatures. We conclude that the microclimate and soil chemical characteristics are the main drivers of changes in protozoan assemblage composition in response to elevation and vegetation.     

Geographical Distribution of Testate Amoebae in Tibet and Northwestern Yunnan and their Relationships with Climate

In Asia, especially in China, our knowledge of the distribution of testate amoebae is still limited. In this paper, the geographical distribution of testate amoebae in Tibetan Plateau and northwestern Yunnan Plateau, southwest China and their relationships with the climatic factors have been studied. We found testate amoebae shifted in the most dominant species and increased in species (or genus) richness from northwest to southeast. Further, the linear regression analyses revealed that both species richness and genus richness have higher positive correlations with the mean temperature of the warmest month and annual mean precipitation as contrasted with the mean altitude, which showed weak negative correlation. This indicates that the temperature and precipitation are more significant influences on the richness than the altitude. The cluster analysis based on the community structure, defined by Sørenson’s coefficient matrix, suggested four groups from the 10 physiographical regions. This geographical distribution pattern was also closely related with the climatic regionalization. The present climatic regionalization pattern of the study area originated from the uplift of Tibetan Plateau and mainly occurred in or after the late Pleistocene. Therefore, the geographical distribution of testate amoebae in our study area may have experienced complicated and drastic changes corresponding to the variation of the climate caused by the geological events.     

Ecology of Testate Amoebae in an Amazonian Peatland and Development of a Transfer Function for Palaeohydrological Reconstruction

Tropical peatlands represent globally important carbon sinks with a unique biodiversity and are currently threatened by climate change and human activities. It is now imperative that proxy methods are developed to understand the ecohydrological dynamics of these systems and for testing peatland development models. Testate amoebae have been used as environmental indicators in ecological and palaeoecological studies of peatlands, primarily in ombrotrophic Sphagnum-dominated peatlands in the mid- and high-latitudes. We present the first ecological analysis of testate amoebae in a tropical peatland, a nutrient-poor domed bog in western (Peruvian) Amazonia. Litter samples were collected from different hydrological microforms (hummock to pool) along a transect from the edge to the interior of the peatland. We recorded 47 taxa from 21 genera. The most common taxa are Cryptodifflugia oviformis, Euglypha rotunda type, Phryganella acropodia, Pseudodifflugia fulva type and Trinema lineare. One species found only in the southern hemisphere, Argynnia spicata, is present. Arcella spp., Centropyxis aculeata and Lesqueresia spiralis are indicators of pools containing standing water. Canonical correspondence analysis and non-metric multidimensional scaling illustrate that water table depth is a significant control on the distribution of testate amoebae, similar to the results from mid- and high-latitude peatlands. A transfer function model for water table based on weighted averaging partial least-squares (WAPLS) regression is presented and performs well under cross-validation (r \(^{2}_{apparent} \,=\, 0.76, \text {RMSE} \,=\, 4.29; \mathrm {r}^{2}_{jack} \,=\, 0.68, \text {RMSEP} \,=\, 5.18\) ). The transfer function was applied to a 1-m peat core, and sample-specific reconstruction errors were generated using bootstrapping. The reconstruction generally suggests near-surface water tables over the last 3,000 years, with a shift to drier conditions at c. cal. 1218-1273 AD.     

Testate amoebae (Protista) communities in Hylocomium splendens (Hedw.) B.S.G. (Bryophyta): relationships with altitude, and moss elemental chemistry

We studied the testate amoebae in the moss Hylocomium splendens along an altitudinal gradient from 1000 to 2200 m asl. in the south-eastern Alps of Italy in relation to micro- and macro-nutrient content of moss plants. Three mountainous areas were chosen, two of them characterised by calcareous bedrock, the third by siliceous bedrock. A total of 25 testate amoebae taxa were recorded, with a mean species richness of 9.3 per sampling plot. In a canonical correspondence analysis, 63.1% of the variation in the amoebae data was explained by moss tissue chemistry, namely by C, P, Ca, Mg, Al, Fe, and Na content and a binary site variable. We interpreted this result as an indirect effect of moss chemistry on testate amoebae through an influence on prey organisms. Although two species responded to altitude, there was no overall significant relationship between testate amoebae diversity or community structure and altitude, presumably because our sampling protocol aimed at minimizing the variability due to vegetation types and soil heterogeneity. This suggests that previous evidence of altitudinal or latitudinal effects on testate amoebae diversity may at least in part be due to a sampling bias, namely differences in soil type or moss species sampled.     

Diversity and Distribution of Freshwater Testate Amoebae (Protozoa) Along Latitudinal and Trophic Gradients in China

Freshwater microbial diversity is subject to multiple stressors in the Anthropocene epoch. However, the effects of climate changes and human activities on freshwater protozoa remain poorly understood. In this study, the diversity and distribution of testate amoebae from the surface sediments were investigated in 51 Chinese lakes and reservoirs along two gradients, latitude and trophic status. A total of 169 taxa belonging to 24 genera were identified, and the most diverse and dominant genera were Difflugia (78 taxa), Centropyxis (26 taxa) and Arcella (12 taxa). Our analysis revealed that biomass of testate amoebae decreased significantly along the latitudinal gradient, while Shannon-Wiener indices and species richness presented an opposite trend (P?P?相似文献   

Diversity and community patterns of testate amoebae in Bau Sen and Bau Trang lakes in Binh Thuan Province,Vietnam

The species composition and distribution of testate amoebae in Bau Sen and Bau Trang lakes (Binh Thuan Province, Vietnam) were investigated. Fifty-three species, varieties and forms have been identified from the water column and sediments. Twenty-seven species, varieties and forms from the genera Arcella, Centropyxis, Cyclopyxis, Difflugia and Pyxidicula were found in Vietnam for the first time. The updated list of testate amoebae in Vietnam now includes 286 taxa. The genera Arcella, Centropyxis and Difflugia are characterized by the highest frequency of occurrence. The species diversity of Arcella, Centropyxis, Difflugia was the highest. Centropyxis aculeata, Arcella discoides, Difflugia schurmanni, Netzelia oviformis and Difflugia limnetica were the most common species. Many species have shown restricted distribution, some species have been found only in one lake and not been found in another lake. The number of observed species, varieties, and forms in each lake is 34. The average number of the species per sample on the shores of the lakes subjected to human agricultural activity was significantly higher than in the samples from the shores of the lakes with less anthropogenic disturbance. The curves of “cumulative species number vs. sampling effort” are well fitted by equations S = 7.60 N ^0.69 for Bau Sen lake and S = 12.52 N ^0.46 for Bau Trang. The curves are unsaturated, which indicates that more intensive investigations of testate amoebae should be expected to reveal more species.     

Biogeography of testate amoebae in the soils of Mexico

We studied testate amoebae (testates) in the soils of coniferous and deciduous forests and in the wetland and aquatic habitats of Mexico. In 141 samples we found 205 taxa identified to the species or intraspecies level and 68 testate amoebae, which could not be identified to the species level. The highest species diversity of testates was found in the soils of the tropical rainforest (126 species and intraspecific taxa, including spp.) and in tropical wetlands (144 species and intraspecific taxa, including spp.). The study documented testate amoebae with a limited geographical distribution (genera Centropyxis, Cornuapyxis, Ellipsopyxis, Hoogenraadia, Planhoogenraadia, Apolimia, Certesella, Apodera, and Alocodera). We found that testate amoebae in the soils of Mexico had a high level of polymorphism and individual variability. We discuss the value of soil testate amoebae for defining biogeographical regions of Mexico.     

The curse of taxonomic uncertainty in biogeographical studies of free-living terrestrial protists: a case study of testate amoebae from Amsterdam Island

Aim A current debate in microbial biogeography contrasts two views concerning the distribution of free‐living microorganisms. The first view assumes a ubiquitous distribution, while the second assumes that at least some species have limited geographical distributions. We tested for limited geographical distributions by identifying testate amoebae morphospecies from an extremely remote oceanic island where the potential for endemism is high. Location Amsterdam Island, Indian Ocean. Methods Sixty moss and water samples collected from the top of the volcano to the lowland were investigated for their testate amoeba content. Due to taxonomic uncertainties among the Argynnia (Nebela) dentistoma species complex (including A. antarctica), we also performed light and scanning electron microscopy investigations on the shell ultrastructure and biometric analyses on several specimens of this taxon. Results We identified a total of 43 testate amoeba taxa belonging to 15 genera. Only four testate amoeba taxa had previously been recorded on this island. Testate amoeba communities of Amsterdam Island are dominated by cosmopolitan ubiquitous euglyphid taxa such as Trinema lineare, Assulina muscorum and Corythion dubium. The length and width ranges for Argynnia dentistoma on Amsterdam Island overlap with other records of this species and of A. antarctica, suggesting that A. antarctica is not a distinct taxon. Main conclusions Although Amsterdam Island is among the most remote islands in the world, an extensive inventory of testate amoeba morphospecies provided no clear evidence for endemism. On the one hand, our detailed morphometric analysis of the A. dentistoma complex revealed that A. antarctica, a morphospecies previously suggested to display endemism, cannot be confidently distinguished from the cosmopolitan morphospecies A. dentistoma. On the other hand, five morphotaxa could not be identified with certainty and might represent new species, potentially with limited distribution. These examples illustrate how taxonomic uncertainties undermine biogeographical studies of testate amoebae. In order to allow better interpretation of morphology‐based testate amoeba distribution data, an assessment of genetic diversity among and within morphotaxa in relation to geographical distance for some common testate amoebae should be given high priority.     

Light variability and mixotrophy: Responses of testate amoeba communities and shell δ13C values to a peatland shading experiment

Paleoecological records suggest that growing season length and/or cloudiness may affect peatland carbon accumulation and testate amoeba-based environmental reconstructions, highlighting a need to understand how light intensity affects microbial communities. We shaded plots on two peatlands for two years to examine effects on testate amoeba communities, the relative abundance of mixotrophic and heterotrophic testate amoebae, transfer-function performance, and δ¹³C values of two species of mixotrophic testate amoebae. Surprisingly, relative abundance of mixotrophic species increased in shade, although compositional changes did not affect transfer-function performance. Shading did not affect δ¹³C values of Hyalosphenia papilio and Heleopera sphagni, which ranged from −23.5 to −19.6‰ and −23.2 to −19.2‰, respectively. These δ¹³C values were higher than those of potential food sources and lower than literature-derived values for Chlorella, the zoochlorellae inhabiting mixotrophic testate amoebae. δ¹³C values thus suggest that these mixotrophic species obtain some carbon from Chlorella, although coupled dietary and isotope studies are needed to quantify this contribution. More research is needed to assess impacts of light variability on peatland microbial communities; however, carbon sources are recorded by δ¹³C values of testate amoebae, indicating potential for studies of carbon cycling and how mixotrophy varies temporally and spatially.     

Seasonal changes in Sphagnum peatland testate amoeba communities along a hydrological gradient

Testate amoebae are an abundant and functionally important group of protists in peatlands, but little is known about the seasonal patterns of their communities. We investigated the relationships between testate amoeba diversity and community structure and water table depth and light conditions (shading vs. insolation) in a Sphagnum peatland in Northern Poland (Linje mire) in spring and summer 2010. We monitored the water table at five sites across the peatland and collected Sphagnum samples in lawn and hummock micro-sites around each piezometer, in spring (3 May) and mid-summer (6 August) 2010. Water table differed significantly between micro-sites and seasons (Kruskal–Wallis test, p = 0.001). The community structure of testate amoebae differed significantly between spring and summer in both hummock and lawn micro-sites. We recorded a small, but significant drop in Shannon diversity, between spring and summer (1.76 vs. 1.72). Strongest correlations were found between testate amoeba communities and water table lowering and light conditions. The relative abundance of mixotrophic species Hyalosphenia papilio, Archerella flavum and of Euglypha ciliata was higher in the summer.     

Influence of Environmental Heterogeneity on the Structure of Testate Amoebae (Protozoa,Rhizopoda) Assemblages in the Plankton of the Upper Paraná River Floodplain,Brazil

In freshwater environments, testate amoebae are usually found associated with macrophytes and sediments and many studies have suggested that their occurrence in plankton samples is accidental. This implies that predictable patterns detected in planktonic assemblages should not be observed in testate amoebae assemblages. This hypothesis was tested in this study. Plankton samples were collected from different environments in the Upper Paraná River floodplain. Results show that patterns in species composition and abundance of testate amoebae are predictable, and that dominant species tend to present characteristic shell morphology in hydrologically different environments. We suggest that testate amoebae must be routinely included in plankton ecology studies, at least in floodplain environments.     

Testate amoebae communities from aquatic habitats in the Arctic

Summary Forty taxa of testate amoebae were found in 15 aquatic samples collected in East Greenland (Angmasssalik Region), Jan Mayen and N.W. Spitsbergen. The number of species per sample is rather small, and the contribution of strictly aquatic species to the fauna is limited. A geographical shift in the importance of some genera can be demonstrated. Centropyxis aerophila and Paraquadrula irregularis are two of the most frequent species. The first-named is characteristic for acidoligotrophic waters, while the latter belongs to an alkaline-mesotrophic community. A third community is named after the commonest species, Trinema lineare. It seems to prefer a somewhat intermediate type of water.     

Testate amoebae and tintinnids as spatial and seasonal indicators in the intertidal margins of Guadiana Estuary (southeastern Portugal)

The present study gathers pioneering taxonomical and community data on testate amoebae and agglutinated tintinnids, analyzing their seasonal and spatial distribution patterns in the mesotidal system of the Guadiana Estuary, southeastern Portugal. To evaluate both groups’ potential as bioindicators in climate monitoring and paleoenvironmental reconstructions, their abundance, diversity and living proportions were compared to elevation in relation to mean sea-level, marine influence and to periods of elevated water levels. The distributions of testate amoebae and tintinnid total assemblages were also related to major physicochemical variables by means of multivariate analysis.From 49 surface sediment samples collected in winter and summer 2010, 17 species (25 strains) of testate amoebae were identified (in the 63 μm fraction). The Centropyxidae, mainly represented by Centropyxis aculeata, Centropyxis arcula and Centropyxis constricta, had the greatest density (71% of total individuals), while the Difflugidae represented the most species (82% of total species). Higher diversities and densities were observed in winter in the upper estuary, where salinity is negligible, and in the middle estuary where they are concentrated at the lower levels of the intertidal zone. Few or no individuals were observed in the highest marsh zones. In winter, dead testate amoebae were dominant, with empty tests accumulating in the sediments from post-mortem transport by high river discharge. In summer, an increase in the living fraction is observed, with living testate amoebae along the entire estuary, which could indicate that some species are able to live in the lower reaches of the estuary.Along with the testate amoebae, two species of agglutinated tintinnids (>63 μm), Stenosemella ventricosa and Tintinnopsis cf. lata, were abundant in the sediments. Their highest abundances were observed in summer. Living individuals were only recorded in summer, mainly in the vicinities of freshwater and sewage outflows, where elevated nutrient concentrations may be expected.The present study demonstrates that both testate amoebae and tintinnids have well defined patterns in their temporal and spatial distribution, offering high bioindicator potential in environmental/climate monitoring studies as well as in paleoenvironmental reconstructions.