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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.

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.

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.

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.

The role of environmental factors that shape the large‐scale distribution of eukaryotic microbes remains understudied. We aimed to disentangle the impacts of latitudinal and longitudinal gradients on the distribution of Sphagnum‐dwelling testate amoebae in mires and to understand the influence of environmental factors related to both local habitats (hummock—lawn—hollows) and regional climates. A range from temperate to subarctic and from the European part to the Far East of Russia (51°–70°N, 32°–158°E). Testate amoeba (Arcellinida, Euglyphida, and Amphitremida). We analysed the testate amoeba (TA) composition and abundance data from 816 samples collected in 75 peatlands. Linear mixed‐effects models and redundancy analysis were applied to determine the likely environmental drivers of TA α‐ and β‐diversity. We identified a significant reversed latitudinal gradient in α‐diversity which negatively correlated with the mean annual temperature. This gradient is microhabitat‐specific, being prominent in lawn and hollow microhabitats, but not in hummocks. Longitude, which corresponds mainly to a gradient of precipitation seasonality, was a significant predictor of TA β‐diversity, especially in hollows. Our findings identify climatic factors (e.g., mean annual temperature and precipitation seasonality) as likely shaping the continental‐scale TA α‐ and β‐diversity patterns, emphasising the microhabitat‐specific nature of these relationships. The absence of pattern in hummocks is interpreted as evidence for a predominant microhabitat stress (i.e., low moisture and pH) in this habitat.

Abstract Testate amoebae are widely distributed organisms, playing essential roles in several aquatic and terrestrial ecosystems. This study presents an overview of the biodiversity of Testate amoebae (Arcellinida and Euglyphida) in the state of Bahia, Brazil, over the last 108 years, based on unpublished data and information from the literature. The records covered 19 municipalities and seven river basins. A total of 172 infrageneric taxa were identified, with Difflugiidae and Arcellidae standing out as the most representative and Centropyxis aculeata as the only constant species (FO = 100%). We observed a total of 25 occurrences that were new to the state. The study considered ecological and methodological aspects, including biomes, types of aquatic bodies, ecosystems, collection methods, mesh sizes, and compartments. Methods such as washing macrophyte rhizospheres and using 20 μm nets have demonstrated greater efficiency in estimating richness. The analysis of accumulation curves indicated that the sampling method recorded approximately 76.3% of the estimated biodiversity. Despite the advances, gaps remain, e.g., in the Cerrado biome, in temporary lakes, and in sediments. This study reinforces the importance of methodological standardization and investment in studies in the Bahia state to improve knowledge about regional and global biodiversity.

Testate amoebae are effective bioindicators of environmental changes in aquatic ecosystems. This study assessed the influence of environmental heterogeneity and seasonality on the structure of testate amoebae assemblages in two Conservation Units in northeastern Brazil: the National Park of Boa Nova (PARNA) and the Wildlife Sanctuary (REVIS), Bahia. Samples were collected from 12 sites during the rainy and dry seasons, alongside abiotic data. We identified 83 taxa, including 26 new records for Bahia. The families Euglyphidae and Hyalospheniidae were the most species-rich. Arcella hemisphaerica Perty, 1852, Centropyxis aculeata (Ehrenberg, 1838), and Euglypha tuberculata Dujardin, 1841 occurred in all samples, with the latter two, along with Cyphoderia ampulla (Ehrenberg, 1840), being the most abundant. Both environmental heterogeneity and season significantly shaped amoebae assemblages, with greater abundance and diversity in the dry season. Rarefaction curves indicated adequate sampling. Cluster analysis distinguished assemblages by rainfall patterns and highlighted the distinctiveness of samples from the Caatinga (P12) compared to ecotonal sites. Redundancy analysis showed that water temperature, transparency, depth, conductivity, dissolved solids, and salinity were key environmental predictors. These findings underscore the importance of considering seasonal and spatial variability in conservation strategies and highlight the relevance of testate amoebae as bioindicators in Neotropical protected areas.

Arcellinida are an abundant and diverse order of testate (shelled) amoebae that are important bioindicators of changing climates. Despite their ecological importance, the molecular mechanisms that underlie their adaptations, including those involving lineage-specific genes, remain largely unknown. Lineage-specific gene families (LSGFs) are linked to evolutionary innovations, yet the evolution of LSGFs remains underexplored across the tree of life, with most research restricted to model eukaryotes. Here, we assess the evolution of Arcellinida-specific gene families using a set of 197 Arcellinida transcriptomes representing 12 Arcellinida genera. We employ a conservative filtering approach to identify 3424 Arcellinda-specific gene families. Our analyses show that these lineage-specific gene families are shorter and exhibit lower expression compared to more conserved genes, congruent with trends observed in other eukaryotic lineages. Although there are inherent limitations regarding missing data with transcriptomics, we recover substantially more lineage-specific gene family births in the symbiont-bearing species Hyalosphenia papilio compared to Hyalosphenia elegans. Our results demonstrate a method to identify lineage-specific genes in non-model organisms where no reference genome are available, and expand our understanding of the evolution of lineage-specific genes in eukaryotes.

Peatlands in southern Chile, particularly in the remote Aysén region, are unique ecosystems that remain understudied despite their ecological significance as natural laboratories. These near-pristine environments serve as essential water reservoirs and harbor largely unexplored microbial diversity. Testate amoebae, a group of shelled protists, play key roles in nutrient cycling and are highly sensitive to environmental changes, making them valuable bioindicators. However, the ecological drivers shaping their diversity and community composition in Chilean peatlands remain poorly understood. This study investigated the spatial distribution and diversity of testate amoebae across five peatlands in the Aysén region (44°S and 49°S; Southern Patagonia, Chile). We recorded 73 morphospecies, including typical southern taxa such as Alocodera cockayni, Apodera vas, Argynnia gertrudeana, Certesella certesi, and C. martiali. Redundancy analysis revealed that organic phosphorus, pH, and sulfate are the most influential factors shaping testate amoeba communities. Beta diversity analysis indicated significant spatial turnover among sites, suggesting that local environmental gradients strongly influence species distribution. Interestingly, Sphagnum-dominated peatlands exhibited higher diversity compared to those with mixed vegetation (vascular plants and bryophytes). Our findings fill a critical gap in understanding microbial biodiversity in Chilean peatlands and highlight the importance of conserving these ecosystems as reservoirs of microbial diversity and natural archives of environmental change.

Abstract: Aim: Testate amoebae are a group that remains understudied. The present study conducted a survey on the testaceans’ records in several biotopes in ecoregions of the State of Rio de Janeiro, exploring differences in the occurrence of taxa. Methods A literature survey was carried out in the Scopus, Web of Science, Google Scholar and Scielo databases using the keywords in English and Portuguese "Testate Amoebae", "Thecamoebian", "Zooplankton" and accompanied by "Rio de Janeiro". Further, samples (collected by plankton mesh nets from 50 to 68 µm; bucket and bottle) from 12 locations were analyzed. The identification of taxa was conducted using an optical microscope with digital camera and Toup-View software for morphological measurements and with specific bibliography. All the records were georeferenced across the freshwater ecoregions of Rio de Janeiro. Statistical analyses were performed using R 4.3.3 Software (R Core Team 2024) through the Vegan package, a species accumulation curve (specaccum function), non-metric multidimensional scaling (nMDS) analysis based on ‘Jaccard’ dissimilarity and the PERMANOVA test performed. Results The bibliographic survey resulted in 35 publications from 1910 to 2023. The sum of records from the literature and from the samples analyzed comprised 37 localities and 250 taxa, including new records for the State of Rio de Janeiro. Centropyxis aculeata was the most frequent species (63.7%), and Difflugia, Centropyxis and Arcella were the most diverse genera. The species accumulation curve indicated that testaceans’ richness is underestimated, evidencing insufficient sampling. There was no significant difference between testaceans’ assemblages from different biotopes. Conclusions The records in Rio de Janeiro are underestimated due to insufficient sampling in some ecoregions. Future studies are needed to produce a taxonomic inventory more faithful real diversity.