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Testate amoebae are known among the proxies for paleolimnological investigations but, despite their recognized importance and recent findings, they have not been sufficiently studied in alpine lakes, particularly in Europe. The present study analyzes fossil testate amoeba assemblages from the Upper Balma Lake (2216 m a.s.l., Western Alps, Italy) to reconstruct ecological changes over the past 1200 years. 21 species belonging to 5 genera were identified, with Centropyxis and Difflugia being the most abundant. Multivariate statistical analyses, combined with sedimentological and geochemical data, revealed five paleoenvironmental phases corresponding to known climatic events, including the Medieval Climate Anomaly, the Little Ice Age, and the Recent Warming period. Assemblage composition and diversity were related to grain size variations, nutrient input, and trace element concentrations (e.g., As, Mn, Mo) and periods of climatic stability were associated with higher biodiversity, while cold or disturbed intervals, marked by floods or sediment reworking, resulted in reduced abundances and diversity. In recent decades, a decline was observed for the genus Centropyxis , possibly indicating reduced oxygenation and changes in contaminant levels. Comparative analysis with the Lower Balma Lake, located downstream in the same area, highlighted the influence of morphological/hydrological differences between lakes on species distributions. The findings underscore the value of testate amoebae as sensitive bioindicators and their applicability in paleoecological reconstructions of alpine lakes. This study contributes to understanding long-term ecological responses to climate change and provides insights into flood regime variability in high-mountain environments.

Peatlands are susceptible not only to direct disturbance, but also to indirect changes in their surroundings, including land management. Changes in agricultural practices or forest management can significantly influence peatland functioning, for example, their trophic status or surface vegetation. Here, we investigate the effects of planned forestry on two Sphagnum -dominated peatlands in northern Poland’s Tuchola Forest. We use testate amoebae and compare them to available pollen and historical data to reconstruct past environmental conditions and assess anthropogenic pressure. The Tuchola Forest has undergone significant transformations as a result of human activities, notably during Prussia’s promotion of pine monoculture in the 19th century. We hypothesized that forest management activities and other related disturbances have led to wetland acidification and water table alterations. Our results show that these changes have had profound effects on both peatlands. Radiocarbon dating revealed a correlation between forest management practices and peatland dynamics. Quantitative reconstructions based on testate amoebae showed that, as a result of the introduced pine monoculture, both peatlands experienced rapid acidification (pH levels dropping from ca. 6.2 to 3.5) and water table lowering of over 15 cm. The predominance of pine monoculture has not only reduced biodiversity but also enhanced the susceptibility of the forest to fires and pest outbreaks, further affecting peatland conditions. These findings contribute to understanding of how historical land-use changes continue to influence present-day peatland dynamics, offering insights into restoration and conservation efforts in forested peatland landscapes.

The Quaternary glaciations profoundly shaped the biogeography of plants and animals, yet their impact on microbial eukaryotes remains largely unexplored. We tested the “genetic legacy of the Quaternary” (GLQ) paradigm in terrestrial protists using Arcellinida testate amoebae diversity distribution across the Iberian Peninsula, a well‐established glacial refugium. To do so, we compiled the most extensive Arcellinida metabarcoding dataset to date (ArKOI), including 615 samples from multiple continents and ecosystems. Our results showed that hotspots of intra‐OTU genetic diversity align with known Iberian refugia, supporting the concept of “refugia within refugia,” and displaying clear ecoregion‐specific climatic niches. Patterns of spatial clustering, niche breadth, and historical demographic reconstruction revealed repeated range contractions and expansions during the Pleistocene, mirroring those observed in macro‐organisms. These findings extend the GLQ paradigm to protists, highlighting shared historical and ecological processes across the eukaryotic tree of life and contributing to a unified theory of biogeographic responses to climatic change.

Climate change models point to a possible rise in air temperature, ranging from 2 °C to 4 °C. Global changes will therefore have a particularly pronounced effect on the functioning of shallow water bodies known as peat ponds, i.e., habitats formed after peat extraction in peatlands. However, the extent of this impact is still unknown. The main objective of the study was to determine the impact of water level and water physicochemical properties on the functioning of selected groups of aquatic organisms in peat ponds of different origins. The study was conducted in spring, summer and autumn of the years 2024 and 2025, in 10 peat ponds with different trophic status and typology, located in the Polesie National Park in eastern Poland. Considerable fluctuations in water levels, resulting from a scarcity of precipitation, accelerated the drying out and overgrowth of peat ponds, particularly the alkaline and acidic types. Within the zoocoenotic communities, a significant decline in the abundance of planktonic species and an increase in the abundance of littoral or periphytic species were recorded (F = 6.24, p < 0.015). Regarding trophic structure, an increase in the abundance of mixotrophic species and a decrease in the abundance of top-level predators were observed. Hydrological changes were reflected in an increase in species richness and abundance of communities of organisms with broad ecological tolerance (mainly ciliates), and a decrease in the number of species and abundance of planktonic crustaceans and macroinvertebrates. The RDA model explains over 84% of the total variability, indicating excellent model fit to the data and a strong correlation between environmental variables and species composition. Based on p values, water level, temperature, pH, and COD were selected as significant variables, with conductivity, O2, and Ptot demonstrating less statistical significance. Peat ponds ecosystems can serve as an excellent model system for studying the impact of intensifying climate change on the functioning of shallow water bodies.

Soil microbial communities play a crucial role in the functioning of terrestrial ecosystems. Rapid changes in climate and land-use will likely cause major changes in belowground biodiversity with unknown consequences on ecosystem functioning. The functional traits, taxonomic and functional diversities of soil microorganisms are known to vary in relation to soil type and climate, but few studies have compared these patterns and explored assembly community mechanisms systematically in contrasted ecological conditions. Here we address this gap and focus on testate amoebae, a key group of shell-producing microbial predators known to play significant roles in C and N cycling in terrestrial ecosystem. We used morphological approach to assess and compare their taxonomic and functional diversity in organic (Histosols) and mineral soils in six regions (320 samples) spanning a wide range of latitudes (52–67◦N, ~2126 km) and longitudes (46–107◦E, ~3927 km) in Central-North Eurasia. Our study revealed significant differences in testate amoeba community composition, diversity, functional traits and assembly mechanisms among ecoregions and soil type. In the ecoregions with drier soils, testate amoeba taxonomic and functional diversities were higher in organic soils compared to mineral soils, while the opposite was observed in ecoregions with wetter soils. With respect to morphological traits, in drier-soil ecoregions such as forest-steppes, testate amoebae were longer and had a relatively smaller aperture in organic soils, while the opposite is true in wetter-soil ecoregions such as taiga and tundra. Habitat filtering was identified as the leading assembly process in mineral soils, while biotic factors were more influential in organic soils. This study provides a comprehensive comparative analysis of testate amoeba communities, enhancing our understanding of how abiotic and biotic factors shape microbial communities in ecosystems, highlighting the role of soil moisture regime, and offering valuable insights for predicting ecological responses to environmental changes.

Knowledge about climate changes is crucial for understanding past and current anthropogenic ecosystem changes, but individual palaeoclimate proxies involve different habitat-dependent confounding factors. Continuously ombrotrophic bogs are an excellent system for palaeoclimate reconstructions because their functioning depends tightly on water table depth (WTD), which varies exclusively with the balance between precipitation and temperature. Here, we investigate a 7000-year-long record from the Puścizna Wielka bog (Poland). We focused on developing the first palaeoclimatological reconstruction for the Western Carpathians, which together includes testate amoebae (TA), the isotopic signal in Sphagnum stems (δ13C and δ18O), and plant macrofossils (PM), the latter enabling to trace micro-topographical changes and assess if the consistent ombrotrophic conditions needed for unbiased reconstruction were met. Both the regional (TAREG, PM) and continental (TAEU) calibration training sets were used for quantitative WTD reconstructions. Our WTD reconstructions were compared with the downscaled CCSM3 simulations. Pollen data provided information on the surrounding vegetation. Reconstructed pH and species composition of PM confirmed continual ombrotrophy. At the Middle-Late Holocene boundary (ca 4300–4200 cal yr BP), the TA-rich lawn phase with Sphagnum magellanicum and Eriophorum vaginatum replaced the initial hollow-like phase with Scheuchzeria, Sphagnum sec. Cuspidata and Archerella flavum. The climate driver of this change (decreased humidity) is also suggested by a 100–200 years delayed increase in fir pollen at the expense of spruce. For the last ca 230 years, δ13C and TA suggest that the bog had experienced unprecedented drought. The bog was dominated by Sphagnum rubellum-dwarf shrub hummocks with Alabasta militaris, Assulina muscorum and Hyalosphenia elegans at this time. Apart from these major changes, we identified several other events that are otherwise documented only by individual studies across Europe for the Late Holocene, especially for the Little Ice Age. Six distinctly wet and five distinctly dry periods were consistent among at least two proxies, with a conspicuously warm and dry climate at the beginning of the Bronze Age, allowing human colonisation of previously harsh mountain areas. The consistency with CCSM3 was the highest for TAREG-inferred WTD and lowest for δ18O. The temperature and precipitation of the warmest quarter were the most influential explanatory variables in multiple regression. Additively to CCSM3, isotopes in Sphagnum stems explained some WTD variation reconstructed by TAEU and PM, suggesting a more critical role of the microtopographic position for these proxies. Our results suggest that TA reconcile multiple equivocal reconstructions, reveal subtle fluctuations only occasionally reported by other proxies, and are less affected by climate-independent microtopography. However, the inclusion of PM in palaeoclimatic studies is essential to verify the continuous ombrotrophy of recent bogs.

Testate amoebae are widely used as proxies in palaeoecological reconstructions of lacustrine environments. However, our knowledge on their morphological adaptation to depth is still limited. This study aims to determine correlations between the morphological and size structure of testate amoeba communities and depth and some other environmental variables along a depth gradient from 0 to 57 m in mesotrophic Valdayskoe Lake, Russia. The morphological structure of testate amoeba communities in the bottom surface sediments of the lake and their distribution along the depth gradient were described. Redundancy analysis indicated that sampling depth, temperature, pH, and slope angle significantly explained the total variance in the community compositions, which were classified into three morphological groups. The set of morphotraits of testate amoebae communities differed drastically above and below the thermocline and may be used as an indicator of the depths. Above and below the thermocline, the morphological structure of testaceans is also determined by other environmental variables associated with the habitats they were found. The weighted and median body size of testate amoebae generally decreases with depth, but bottom relief influences the body size structure of the community via differences in the accumulation of organic matter on slopes and flat sites. These data may contribute to a better interpretation of palaeoecological records of subfossil testate amoebae in lacustrine surface sediments and serve as a basis for the development of a transfer function for reconstructing lake depths.

Climate change-induced drying is projected for northern peatlands, but evidence on its extent is inconsistent. Testate amoebae (TA) are a water table depth proxy that also responds to vegetation succession and abiotic changes. However, it is not well-known how TA communities and functional traits differ between unaffected and drying areas in different peatland types. Thus, we compared TA communities and functional traits in undrained control areas and areas (initially similar in vegetation and WT) subjected to moderate water level drawdown (WLD) for ∼20 years. The experiment covers a rich fen, a poor fen, and a bog. Arboreal vegetation has been established in the fen WLD areas. Taxonomic composition and functional traits differed between the WLD and control, most notably in the rich fen and the least in the bog, mirroring the vegetation. Eleven taxa favored WLD or pristine conditions; six taxa had a site-specific preference. Small tests and apertures, heterotrophy, and siliceous tests were more common in the WLD than control areas, but in the bog, these differences were not significant. Overall, besides drying, the establishment of arboreal vegetation and changes in abiotic conditions affected TA community and trait compositions in the fens, showing that they deliver information not only about water table depth but also sensitivity/resistance of peatlands. When aiming for quantitative water table reconstructions, account should be taken that the secondary changes amplify the signal of WLD in fens, whereas the resistance of vegetation and testate amoeba communities may hinder it in bogs, possibly causing bias when the reconstruction runs through a fen-bog-transition.

Since Georges Deflandre published his monograph on the genus Nebela in 1936 no systematic revision of this beautiful group of testate amoebae had been done. In the meantime, the genus was split, and many new species were described. A taxonomic revision was clearly overdue. In this monograph, we present a taxonomic revision of the sub-order Hyalospheniformes (Amoebozoa, Arcellinida), which includes a single family, the Hyalospheniidae. A total of 14 genera, and 97 species are presented in detail. The monograph includes taxonomic keys; taxon descriptions; ecological, geographical, and taxonomical notes; annotated lists of dubious and incertae sedis species; a list of synonymous names; notes on molecular data; and light and scanning electron microscopic pictures; and/or original line drawings for each species. This book is designed to benefit protistologists in general, and particularly ecologists and palaeoecologists, by assisting with the ease and accuracy of identification of hyalospheniid testate amoeba species, many of which are useful bioindicators. We also hope that this book will serve as a useful basis for future work regarding the taxonomy, biogeography, and ecology of these beautiful organisms. Joseph Leidy famously once wrote “How can life be tiresome sol long as there is still a new rhizopod undescribed?” There is no shortage of new Hyalospheniformes awaiting to being described. We hope this book will make the life of passionate taxonomists easier!

Arcella gibbosa is a cosmopolitan testate amoeba species whose distribution and morphological and morphometric characteristics have been well studied. At the same time, the influence of cultivation conditions on this species remains unclear. This work, for the first time, provided comparisons of its shell morphology, morphometric characteristics, and elemental composition of the shell among A. gibbosa populations from natural environments and in culture conditions. The external morphology of the species was similar among the populations grown under various cultivation conditions and in natural habitats, but there were statistically significant differences in each morphometric characteristic, including shell diameter, shell height, and apertural diameter. The results of PERMANOVA, followed by pairwise permutational MANOVAs and NMDS analyses, confirmed statistically pairwise differences between the natural populations and those grown in modified Wright's Chu #10 (mWC) and Prescott–James (PJ) media in terms of the composition of the investigated morphometric characters. Similarly, the results of the PERMANOVA and NMDS analyses revealed a statistically significant difference in shell elemental composition between the mWC and PJ populations. For the first time, we demonstrated the significant effects of culture media, initial cell density, light intensity, and ambient temperature on the growth of this species. Our findings suggest that the cultivation of A. gibbosa in mWC medium under certain conditions, such as a starting density of 20 ind. mL−1, light intensity of 200 lx and ambient temperature of 25 °C, is optimal for obtaining the high and stable cell density to use this species in ecotoxicological studies.