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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.

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.

Testate amoebae are a group of unicellular free-living protozoa which are characterized by morphologically distinct shells (tests) which play an important role in the natural ecosystems as bio-indicators. This communication reports 2 new additions of moss inhabitant testate amoebae viz., Centropyxis lata Jung, 1942 and Centropyxis longispina Decloitre, 1979 to Indian testate fauna from Sholayar forest reserve, Kerala and Singalila National Park, West Bengal.

Inland saline lakes are dynamic environments with fluctuating salinity levels, sometimes reaching values higher than those of seawater. Their abiotic conditions are often extreme and more unpredictable than in marine systems, which could imply lower biotic pressures. This could have allowed nonmarine organisms to cross the salinity barrier and subsequently specialize and diversify there. Alternatively, inland saline lakes could host generalist species that are also found in other environments. In order to answer this question, we focused on a group of protists characterized by their narrow ecological tolerance, Arcellinida testate amoebae. We studied their diversity using a metabarcoding approach in different thalassic and athalassic saline systems from Spain and Chile. The majority of operational taxonomic units (OTUs) were exclusive to athalassohaline systems. Three clades included most diversity in athalassohaline systems, in addition to several specific colonization events. Inland saline systems have been colonized by freshwater species, which diversified there, turning these athalassohaline environments into hotspots of specialized Arcellinida biodiversity.

Many UK blanket bog peatlands are degraded due to historical management including drainage, leading to reduced biodiversity, carbon sequestration and water storage. Currently, much restoration efforts including rewetting and revegetation strategies are being deployed aiming to restore habitats towards intact and ecohydrologically functioning ecosystems. However, it remains unclear how these efforts affect the key microbial consumers, testate amoebae (TA), especially their functional traits, and whether TA can be used as a generic tool to monitor the long-term hydrological restoration success. This study compared TA communities and their key functional traits at one intact and three near-intact sites versus three modified blanket bog sites with different habitat conditions (i.e., least modified, post-restoration, and degraded) to assess their environmental responses, bioindicator potential and explore their possible functional contribution to ecosystems in the process of recovery. The results showed: 1) TA community composition gradually changes from degraded to intact sites in both Sphagnum and surface peat, with distinct dominant TA species in each; 2) soil moisture, Sphagnum cover, and phosphorus content strongly relate to TA composition; 3) Hyalosphenia subflava and Corythion dubium indicate dry conditions, while Archerella flavum and Amphitrema wrightianum are indicators of wet conditions; 4) significantly higher community-weighted mean values of TA traits (biovolume, aperture width, siliceous tests) in surface peat at the least modified areas suggest TA's strong role in carbon and silica cycling following rewetting. Our findings support TA as bioindicators for tracking habitat hydrological conditions and restoration progress in blanket bogs, effectively linking community composition to ecosystem functions.