Arcella

Abstract: Testate amoebae are amoeboid protists inhabiting a test (shell) They occur globally in soils, wetlands and freshwater, especially peats and mosses They are of ancient origin, dating from at least the Mesozoic, with possible ancestors as old as the Neoproterozoic Approximately 2,000 taxa have been described—a number which could easily rise to 4,000 with comprehensive recording Whilst many protists appear to be cosmopolitan as morphospecies, some of the larger testate species (exceeding 100 μm) have long been considered, controversially, to be geographically restricted Definitive conclusions have often been confounded by gaps in distributional data and misidentification Recent increases in recording from previously little known regions, and the rise of molecular taxonomy, have started to resolve outstanding issues—processes still far from complete Accordingly, biogeographical studies have concentrated on “flagship” species—those which can be identified with certainty and are sufficiently recorded to determine their ecological ranges Apodera vas (Certes) has been proved to be largely restricted to the Gondwanaland continents and sub-Antarctic islands, but absent from the Holartic despite the availability of much suitable habitat An early analysis postulated a Mesozoic origin of the species and a distribution influenced by continental drift Recent molecular evidence could imply a later origin Either way, its current distribution is clearly influenced by the pattern of global wind currents and lack of lowland tropical habitat By contrast a “Gondwana-tropical” group of species appears to be restricted to latitudes unaffected by glaciation Instances of local endemism, such as restriction to a single island, are also known, which await molecular evidence for substantiation

Abstract: Testate amoebae are common inhabitants of moist soils, wetland, and lacustrine habitats. They produce a decay-resistant test, or shell, which can be identified to species in most cases and recovered from sediments in quantities sufficiently large to permit estimation of relative abundance. The objectives of this study were to assess the potential of testate amoeba assemblages as paleoenvironmental and environmental indicators in two Lake Superior coastal wetlands and to determine if morphological variation in four common taxa (Arcella spp., Assulina spp., Centropyxis cassis type, and Nebela tincta-parvula-collaris group) is related to microenvironment. Study localities included ridge-swale wetland systems adjacent to Grand Traverse Bay and Tahquamenon Bay in the Upper Peninsula of Michigan. Testate amoeba assemblages from 74 microsites were compared with percent moisture, depth to water table, pH, porosity, depth of living moss, and associated moss and vascular plant species. Morphometric analysis (e.g., test length and aperture diameter) was conducted on 25 individuals from at least 10 microsites for each of the four selected taxa. Gradient analysis indicated that testate amoeba assemblages are primarily controlled by substrate moisture and pH, consistent with results from other regions. Transfer functions for pH and substrate moisture were developed using ‘jack-knifed’ validation procedures. Little relationship was found between microenvironmental parameters and morphological variation in the investigated taxa, except for the Nebela tincta-parvula-collaris group, where test size was significantly correlated with pH (r2 = 0.68). Results indicate that wetland testate amoeba assemblages in these coastal wetland systems are sensitive environmental and paleoenvironmental indicators that can be used to monitor and reconstruct water-level or pH changes.

Abstract: 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.

Abstract: Thecamoebian faunas identified from 15 small permanent and ephemeral lakes and ponds on Barbados, West Indies, are characterized by low numbers of individuals and low species diversities (Shannon-Wiener Diversity Index = 0–1.4). Four lakes and ponds were found to contain no thecamoebians. The faunas were dominated by Centropyxis aculeata , with lesser numbers of Arcella vulgaris , Cucurbitella tricuspis , Centropyxis constricta and Cyclopyxis kahli . Very low numbers of the small idiosomic species Euglypha rotunda and an undifferentiated Corythion-Trinema type were also reported; the first records from a tropical region. Centropyxid-dominated faunas have been reported from other tropical areas and may indicate stressed environmental conditions. Additional important ecological controls on these faunas include substrate characteristics, the nature of bankside and aquatic vegetation and water depth. Land use characteristics do not appear to have a significant influence on faunal distribution, although the soil indicator thecamoebian species C. kahli seems to have been introduced into at least one pond through erosion from adjacent fields. Significant numbers of the salt marsh foraminiferid Jadammina macrescens , and lesser numbers of Polysaccammina ipohalina and Miliammina fusca , were found in one coastal pond, with a few specimens of J. macrescens found in another. The presence of this unusual, nonmarine foraminiferal fauna may relate to the intrusion of salt water into local ground waters, or possibly the introduction of sea salt from the prevailing Atlantic winds. Foraminiferal and thecamoebian colonization into the ponds may have been avian mediated.