Testate amoebae

Testate amoebae are microorganism with one pseudopode like a simple lip or filiform, bentics, with an agglutinate or autogenetic test like-bag; in the fossil record, mostly present in peat deposits, fresh water sediments and some marsh deposits, and they become as environmental proxys at low pH environments, where mollusk or ostracods tend to dissolve. Sampling sediments was carried out on the shoreline and the lagoon bottom, testate amoebae was extracted, counted, and analyzed under the microscope, resulting in the characterization of the shoreline and lagoon bottom assemblage. A total of 34 species are recognized and 9 undifferentiated species, with the most abundant genus Centropyxis, Difflugia and Sphenoderia, and with the dominant species Centropyxis aculeata, Difflugia urceolata, Sphenoderia lenta and Difflugia lanceolata.

Cryptotephra (particles <125 μm) is a key record for monitoring past and current volcanic activity. However, its extraction from the host sediment and analysis is often long and difficult because of its small size. Finding a simple method to extract cryptotephra from environmental samples would therefore make its analysis much easier. We hypothesized that arcellinid testate amoebae may hold such a potential. These free-living shelled protists are among the earliest microorganisms to colonize volcanic tephra, and build their shell by agglutinating minerals from their environment. We analyzed by X-ray Spectrometry the mineral signature of tephra from the 2011 Puyehue-Cordon Caulle Volcanic Complex(Chile) eruption ash fallout and compared it to that of the shells of 51 individual testate amoebae (three individuals from each of 17 species) from 13 samples collected at different distances from the active vent. The mineral composition of particles within shells closely matched that of similar size class particles from their environment. The capacity of testate amoebae to randomly use mineral grains from their environment makes it possible to use their shells to assess the mineral composition of cryptotephra from soil, peat or sediment samples. Testate amoebae therefore represent the microbial world's version of Cinderella's helping pigeons.

AimTo assess the largely neglected patterns and causes of latitudinal diversity gradients in soil protists, using South American testate amoebae as model organisms.To assess the largely neglected patterns and causes of latitudinal diversity gradients in soil protists, using South American testate amoebae as model organisms.LocationSouth-western South America (SSA).South-western South America (SSA).MethodsWe assessed the relationship among richness, latitude and predictions of eight ecological hypotheses in SSA, a region characterized by harsh abiotic conditions northward and southward from mid-latitudes. We also examined the patterns of latitudinal variation in species range sizes, species composition and phylogenetic relatedness among species to assess whether the responses of species to current climate rely on evolutionary constraints.We assessed the relationship among richness, latitude and predictions of eight ecological hypotheses in SSA, a region characterized by harsh abiotic conditions northward and southward from mid-latitudes. We also examined the patterns of latitudinal variation in species range sizes, species composition and phylogenetic relatedness among species to assess whether the responses of species to current climate rely on evolutionary constraints.ResultsRichness followed a unimodal trend with abrupt declines northward and southward from mid-latitudes. This trend was mostly explained by water–energy balance. To our knowledge, this mechanism has never been reported for soil microorganisms before. Species range sizes were larger northward and southward from mid-latitudes, a pattern which we have called the ‘two-way Rapoport effect’. Species composition was due to turnover at mid-latitudes and to nestedness towards low and high latitudes. Species at mid-latitudes tended to be less related to each other than those at low and high latitudes, supporting the existence of evolutionary constraints to water–energy availability.Richness followed a unimodal trend with abrupt declines northward and southward from mid-latitudes. This trend was mostly explained by water–energy balance. To our knowledge, this mechanism has never been reported for soil microorganisms before. Species range sizes were larger northward and southward from mid-latitudes, a pattern which we have called the ‘two-way Rapoport effect’. Species composition was due to turnover at mid-latitudes and to nestedness towards low and high latitudes. Species at mid-latitudes tended to be less related to each other than those at low and high latitudes, supporting the existence of evolutionary constraints to water–energy availability.Main conclusionsThe unimodal response of species diversity to water and energy availability stems from a combination of the ancestral adaptation of testate amoebae to warm, humid climates and past climate changes that set up permanent harsh abiotic conditions northward and southward from mid-latitudes. Given that other soil microorganisms also depend on water and energy to survive and reproduce, we predict that the unimodal response to water–energy balance observed will also be valid for a large number of microbial groups in SSA. While this diversity trend may not hold true for testate amoebae from other regions, we predict that their evolutionary constraints to water–energy availability will always produce strong relationships among richness, water and energy at large spatial-scales.The unimodal response of species diversity to water and energy availability stems from a combination of the ancestral adaptation of testate amoebae to warm, humid climates and past climate changes that set up permanent harsh abiotic conditions northward and southward from mid-latitudes. Given that other soil microorganisms also depend on water and energy to survive and reproduce, we predict that the unimodal response to water–energy balance observed will also be valid for a large number of microbial groups in SSA. While this diversity trend may not hold true for testate amoebae from other regions, we predict that their evolutionary constraints to water–energy availability will always produce strong relationships among richness, water and energy at large spatial-scales.

S ummar y. Our research confirmed the value of kettle-hole mires for reconstructing Holocene environmental changes. The multi-proxy approach in which three palaeoecological methods were used (analyses of testate amoebae, plant macrofossils and pollen) improved the interpretation potential. We studied two Sphagnum mires situated in Tuchola Pinewoods (N Poland). In Tuchola mire 9000 years of environmental changes (groundwater level and pH) were recorded. Water table changes inferred from Tuchola ...

Three radiocarbon-dated sediment cores (4.2 kya to present) from Aktun Ha (Carwash) Cave, Mexico indicate that sediments in flooded caves document Holocene environmental changes. Three distinct environmental phases were determined based on microfossils (shelled rhizopods), organic geochemistry (delta13C, delta15N, TOC, TN, C/N), and particle size distributions (PSDs). In the three cores, terrestrial organic matter was more prevalent in the core closer to the cave entrance (cenote), whereas, aquatic organic matter was more prevalent in cores deeper into the cave. Euryhaline foraminifera (78%) indicate high oligohaline conditions in the freshwater lens (salinity 3.5 - 5.0 psu) during Phase 1 (preceding 4.3 kya), which had higher hydrologic flow rates as interpreted from low organic OM deposition (less than 10%). Phase 2 (4.2 - 2.7 ky BP) is characterized by oscillations between testate amoebae (centropyxids), euryhaline foraminifera (Ammonia tepida var. juvenile), and variable delta15N values. The increases in testate amoebae from Phase 1 and up to 2.50/00 enrichment in delta15N values coupled with poorly sorted PSDs indicate repeated freshening of the freshwater lens (ca. 3.5 - 2.5 psu shift) and associated transport of terrestrial organic matter into the cave. Phase 3 is marked by the colonization of Lagenodifflugia vas at 2.76 ky BP, indicating the onset of modern salinity (1.5 psu) conditions in the local freshwater lens. This is synchronous with a significant reduction in the C/N ratio, and long-term stabilization in sedimentation. The onset of modern hydrologic flow rates in the freshwater lens (less than 1.5 m/s) contributes to increased algae populations in the cenote, increased abundance of organic matter in the cave (TOC greater than 46%). The observed environmental shifts in the cave sediments correlate well with local precipitation changes and storm activity associated with southward migration of the Intertropical Convergence Zone during the late Holocene. Importantly, these results indicate (1) that climate exudes greater control on the phreatic cave environment and aquifer than previously documented, and (2) sediment accumulations in phreatic caves contain viable climate archives, which represent a significantly unexplored source of paleoclimate data.