Multi-scale beta-diversity patterns in testate amoeba communities: species turnover and nestedness along a latitudinal gradient.

The relationship between species diversity and spatial scale is a central topic in spatial community ecology. Latitudinal gradient is among the core mechanisms driving biodiversity distribution on most scales. Patterns of ß-diversity along latitudinal gradient have been well studied for aboveground terrestrial and marine communities, whereas soil organisms remain poorly investigated in this regard. The West Siberian Plain is a good model to address diversity scale-dependence since the latitudinal gradient does not overlap with other possible factors such as elevational or maritime. Here, we collected 111 samples following hierarchical sampling (sub-zones, ecosystem types, microhabitat and replicate samples) and performed multi-scale partitioning of ß-diversity of testate amoeba assemblages as a model of study. We found that among-ecosystem ß-diversity is a leading scale in testate amoeba assemblages variation. Rare species determine ß-diversity at all scale levels especially in the northern regions, where rare taxa almost exclusively accounted for the diversity at the ecosystem level. ß-Diversity is generally dominated by the turnover component at all scales in lower latitudes, whereas nestedness prevailed at among-ecosystem scale in higher latitudes. These findings indicate that microbial assemblages in northern latitudes are spatially homogeneous and constrained by historical drivers at larger scales, whereas in southern regions, it is dominated by the turnover component both at the microhabitat and ecosystem scales and therefore determined by recent vegetation and environmental heterogeneity. Overall, we have provided the evidence for the existence of negative latitudinal gradient for among-ecosystem ß-diversity but not for among-microhabitat and among-sample ß-diversity for terrestrial testate amoeba communities.

Insights into the origin of metazoan multicellularity from predatory unicellular relatives of animals.

BACKGROUND: The origin of animals from their unicellular ancestor was one of the most important events in evolutionary history, but the nature and the order of events leading up to the emergence of multicellular animals are still highly uncertain. The diversity and biology of unicellular relatives of animals have strongly informed our understanding of the transition from single-celled organisms to the multicellular Metazoa. Here, we analyze the cellular structures and complex life cycles of the novel unicellular holozoans Pigoraptor and Syssomonas (Opisthokonta), and their implications for the origin of animals. RESULTS: Syssomonas and Pigoraptor are characterized by complex life cycles with a variety of cell types including flagellates, amoeboflagellates, amoeboid non-flagellar cells, and spherical cysts. The life cycles also include the formation of multicellular aggregations and syncytium-like structures, and an unusual diet for single-celled opisthokonts (partial cell fusion and joint sucking of a large eukaryotic prey), all of which provide new insights into the origin of multicellularity in Metazoa. Several existing models explaining the origin of multicellular animals have been put forward, but these data are interestingly consistent with one, the "synzoospore hypothesis." CONCLUSIONS: The feeding modes of the ancestral metazoan may have been more complex than previously thought, including not only bacterial prey, but also larger eukaryotic cells and organic structures. The ability to feed on large eukaryotic prey could have been a powerful trigger in the formation and development of both aggregative (e.g., joint feeding, which also implies signaling) and clonal (e.g., hypertrophic growth followed by palintomy) multicellular stages that played important roles in the emergence of multicellular animals.

Biodiversity of testate amoebae in Sphagnum bogs: the dataset from forest-steppe ecotone (Middle Volga Territory, Russia).

Background: Testate amoebae are a polyphyletic group of unicellular eukaryotic organisms that are characterised by a rigid shell and inhabit mostly freshwater and terrestrial ecosystems. They are particularly abundant in peatlands, especially in Sphagnum-dominated biotopes. Peatland hydrology is the most important influence on testate amoebae communities. The good preservation of the shells in peat deposits and their response to hydrological regime changes are the principles for palaeohydrological reconstructions. Any changes in the water balance of mires should be expected to have far-reaching effects on biogeochemical cycles, productivity, carbon dioxide and methane exchange. New information: This paper presents a dataset (Darwin Core Archive - DwC-A) on the distribution of Sphagnum-dwelling testate amoebae in nine mires located in the forest-steppe subzone of the East European Plane. The dataset includes information about 86 taxa belonging to 29 genera and contains 3,123 occurrences of 49,874 individuals. The following environmental variables are provided: microtopography, oxidising and reducing potential, total mineralisation, substrate temperature, acidity, substrate wetness and water table depth. These data might be used for biogeographical and palaeoecological studies, including quantitative reconstructions.

Functional traits data for testate amoebae of Northern Holarctic realm.

The functional traits of soil protists have been employed in ecological research to enhance comprehension of the underlying mechanisms of ecological processes. Among the numerous soil protists, testate amoebae emerge as a prominent and abundant group, playing a pivotal role in soil micro-food webs. Furthermore, they are regarded as valuable bioindicators for environmental monitoring and palaeoecological studies due to their sensitivity to environmental changes. We screened 372 testate amoebae species widely distributed across Northern Holarctic realm and collected trait data, representing the morphological and feeding characteristics of testate amoebae. The dataset would provide valuable basis for investigation of the functional diversity and ecological roles of testate amoebae, thus facilitating further research on soil protist communities and ecosystem dynamics.

Distribution of soil testate amoeba assemblages along an elevation gradient on Mount Fuji (Japan).

Elevation gradients have been useful to study distributional patterns of soil organisms since the time of Humboldt but only recently these patterns have been studied for soil microorganisms. Here we report the results on species diversity and composition of soil- and moss-dwelling testate amoeba assemblages along a 1400 m elevation gradient (904-2377 m a.s.l.) on Mount Fuji (Japan) from temperate forest to alpine vegetation. In total, 95 testate amoeba taxa belonging to 29 genera were identified. The core of testate amoeba assemblages was formed by ubiquitous species such as Trinema lineare, Euglypha laevis, Cryptodifflugia oviformis, and Trinema complanatum. However, several taxa with limited geographic distribution were also observed (e.g., Centropyxis latideflandriana, C. stenodeflandriana, Plagiopyxis cf. barrosi, Heleopera rectangularis, and Distomatopyxis couillardi). Species diversity indices (species richness and Shannon's index) were characterised by bell-shaped patterns peaking at âˆ¼ 1700 m in the subalpine mixed conifer-deciduous forest. The species composition of testate amoeba assemblages was best explained by the vegetation types which accounted for 12.3% of the total variation. Overall, these findings indicate that elevation effects on species composition of testate amoeba assemblages are strongly mediated by vegetation.

Key periods of peatland development and environmental changes in the middle taiga zone of Western Siberia during the Holocene.

The response of peatlands to climate change can be highly variable. Through understanding past changes we can better predict the response of peatlands to future climate change. We use a multi-proxy approach to reconstruct the surface wetness and carbon accumulation of the Mukhrino mire (Western Siberia), describing the development of the mire since peat formation in the early Holocene, around 9360 cal. year BP. The mire started as a rich fen which initiated after paludification of a spruce forest (probably in response to a wetter climate), while the Mukhrino mire progressed to ombrotrophic bog conditions (8760 cal. year BP). This transition coincided with the intensive development of mires in Western Siberia and was associated with active carbon accumulation (31 g m-2 year-1). The ecosystem underwent a change to a tree-covered state around 5860 cal. year BP, likely in response to warming and possible droughts and this accompanied low carbon accumulation (12 g m2 year-1). If the future climate will be warmer and wetter, then regional mires are likely to remain a carbon sink, alternatively, a reversion to the wooded state with reduced carbon sink strength is possible.

Size compartmentalization of energy channeling in terrestrial belowground food webs.

Size-structured food webs form integrated trophic systems where energy is channeled from small to large consumers. Empirical evidence suggests that size structure prevails in aquatic ecosystems, whereas in terrestrial food webs trophic position is largely independent of body size. Compartmentalization of energy channeling according to size classes of consumers was suggested as a mechanism that underpins functioning and stability of terrestrial food webs including those belowground, but their structure has not been empirically assessed across the whole size spectrum. Here we used stable isotope analysis and metabolic regressions to describe size structure and energy use in eight belowground communities with consumers spanning 12 orders of magnitude in living body mass, from protists to earthworms. We showed a negative correlation between trophic position and body mass in invertebrate communities and a remarkable nonlinearity in community metabolism and trophic positions across all size classes. Specifically, we found that the correlation between body mass and trophic level is positive in the small-sized (protists, nematodes, arthropods below 1 µg in body mass), neutral in the medium-sized (arthropods of 1 µg to 1 mg), and negative in the large-sized consumers (large arthropods, earthworms), suggesting that these groups form compartments with different trophic organization. Based on this pattern, we propose a concept of belowground food webs being composed of (1) size-structured micro-food web driving fast energy channeling and nutrient release, for example in microbial loop; (2) arthropod macro-food web with no clear correlation between body size and trophic level, hosting soil arthropod diversity and subsidizing aboveground predators; and (3) "trophic whales," sequestering energy in their large bodies and restricting its propagation to higher trophic levels in belowground food webs. The three size compartments are based on a similar set of basal resources, but contribute to different ecosystem-level functions and respond differently to variations in climate, soil characteristics and land use. We suggest that the widely used vision of resource-based energy channeling in belowground food webs can be complemented with size-based energy channeling, where ecosystem multifunctionality, biodiversity, and stability are supported by a balance across individual size compartments.

Erratum: Future Temperature Extremes Will Be More Harmful: A New Critical Factor for Improved Forecasts.

The authors would like to correct the names and surnames of both authors of their previous paper [1] as follows [...].

New Lineage of Microbial Predators Adds Complexity to Reconstructing the Evolutionary Origin of Animals.

The origin of animals is one of the most intensely studied evolutionary events, and our understanding of this transition was greatly advanced by analyses of unicellular relatives of animals, which have shown many "animal-specific" genes actually arose in protistan ancestors long before the emergence of animals [1-3]. These genes have complex distributions, and the protists have diverse lifestyles, so understanding their evolutionary significance requires both a robust phylogeny of animal relatives and a detailed understanding of their biology [4, 5]. But discoveries of new animal-related lineages are rare and historically biased to bacteriovores and parasites. Here, we characterize the morphology and transcriptome content of a new animal-related lineage, predatory flagellate Tunicaraptor unikontum. Tunicaraptor is an extremely small (3-5 µm) and morphologically simple cell superficially resembling some fungal zoospores, but it survives by preying on other eukaryotes, possibly using a dedicated but transient "mouth," which is unique for unicellular opisthokonts. The Tunicaraptor transcriptome encodes a full complement of flagellar genes and the flagella-associated calcium channel, which is only common to predatory animal relatives and missing in microbial parasites and grazers. Tunicaraptor also encodes several major classes of animal cell adhesion molecules, as well as transcription factors and homologs of proteins involved in neurodevelopment that have not been found in other animal-related lineages. Phylogenomics, including Tunicaraptor, challenges the existing framework used to reconstruct the evolution of animal-specific genes and emphasizes that the diversity of animal-related lineages may be better understood only once the smaller, more inconspicuous animal-related lineages are better studied. VIDEO ABSTRACT.

Future Temperature Extremes Will Be More Harmful: A New Critical Factor for Improved Forecasts.

There is increasing evidence that extreme weather events such as frequent and intense cold spells and heat waves cause unprecedented deaths and diseases in both developed and developing countries. Thus, they require extensive and immediate research to limit the risks involved. Average temperatures in Europe in June-July 2019 were the hottest ever measured and attributed to climate change. The problem, however, of a thorough study of natural climate change is the lack of experimental data from the long past, where anthropogenic activity was then very limited. Today, this problem can be successfully resolved using, inter alia, biological indicators that have provided reliable environmental information for thousands of years in the past. The present study used high-resolution quantitative reconstruction data derived from biological records of Lake Silvaplana sediments covering the period 1181-1945. The purpose of this study was to determine whether a slight temperature change in the past could trigger current or future intense temperature change or changes. Modern analytical tools were used for this purpose, which eventually showed that temperature fluctuations were persistent. That is, they exhibit long memory with scaling behavior, which means that an increase (decrease) in temperature in the past was always followed by another increase (decrease) in the future with multiple amplitudes. Therefore, the increase in the frequency, intensity, and duration of extreme temperature events due to climate change will be more pronounced than expected. This will affect human well-being and mortality more than that estimated in today's modeling scenarios. The scaling property detected here can be used for more accurate monthly to decadal forecasting of extreme temperature events. Thus, it is possible to develop improved early warning systems that will reduce the public health risk at local, national, and international levels.

Diversity and Distribution of Free-living Ciliates from High-Arctic Kara Sea Sediments.

For the first time, free-living ciliates were studied in sediments from a variety of habitats in the Kara Sea (the Arctic Ocean). Ciliates were found in a wide range of environmental conditions (from the intertidal zone up to depths of 554m, from salinities ranging from 0 to 34psu, and from coarse sands and gravel to muddy sediments), with total abundances varying from 1 to 127ind/cm3. Altogether, 114 species were identified, most of which were widely distributed and were previously reported from other Arctic regions. An unsaturated species accumulation curve and the presence of many rare species indicated that the Kara Sea is potentially as rich in ciliates as other regions. Fine- and medium-grained sands exhibited the richest and most abundant ciliate fauna, with many interstitial forms occurring up to depths of 200m; whereas both the coarse sands of the exposed intertidal beaches and the sublittoral muds were poorly inhabited by non-specific euryoecious species. The granulometric composition of sediments was suggested to be the main driver controlling the diversity and composition of ciliate communities, while the other factors, such as salinity, water productivity and depth, were of secondary importance.

What is the optimum sample size for the study of peatland testate amoeba assemblages?

Testate amoebae are widely used in ecological and palaeoecological studies of peatlands, particularly as indicators of surface wetness. To ensure data are robust and comparable it is important to consider methodological factors which may affect results. One significant question which has not been directly addressed in previous studies is how sample size (expressed here as number of Sphagnum stems) affects data quality. In three contrasting locations in a Russian peatland we extracted samples of differing size, analysed testate amoebae and calculated a number of widely-used indices: species richness, Simpson diversity, compositional dissimilarity from the largest sample and transfer function predictions of water table depth. We found that there was a trend for larger samples to contain more species across the range of commonly-used sample sizes in ecological studies. Smaller samples sometimes failed to produce counts of testate amoebae often considered minimally adequate. It seems likely that analyses based on samples of different sizes may not produce consistent data. Decisions about sample size need to reflect trade-offs between logistics, data quality, spatial resolution and the disturbance involved in sample extraction. For most common ecological applications we suggest that samples of more than eight Sphagnum stems are likely to be desirable.

Morphology and phylogeny of the testate amoebae Euglypha bryophila Brown, 1911 and Euglypha cristata Leidy, 1874 (Rhizaria, Euglyphida).

The genus Euglypha contains the largest number of filose testate amoeba taxa which were mainly described based on the morphological characteristics of shells. Despite the increasing amount of molecular data, the phylogenetic relationships within the genus Euglypha remain unresolved. In this work we provide new data on SSU rRNA gene sequences, light and electron microscopy for the two euglyphid species Euglypha bryophilaBrown, 1911 and Euglypha cristataLeidy, 1874. Both species are characterised by the presence of a turf of spines on the aboral pole of the shells but differ in shell cross sections (elliptical and circular, respectively). A newly revealed feature of E. bryophila is a three-lobed thickening at the anterior margin and an elongated lobe at the posterior margin of apertural plates. The phylogenetic analysis shows that the species group together with the previously sequenced taxa of the genus Euglypha according to the shell cross-section. The subdivision of the genus based on the shell symmetry may reflect evolutionary trends to complication of the shell from radial to biradial symmetry. We also suggest that the shape of the anterior thickening of apertural plates and the lobe at the posterior margin can be used to distinguish Euglypha at the species level.

An Estimation of the Global Diversity and Distribution of the Smallest Eukaryotes: Biogeography of Marine Benthic Heterotrophic Flagellates.

Protists are ubiquitous, but the factors influencing their diversity and biogeography remain unclear. We use a comprehensive database on the marine benthic heterotrophic flagellate (HF) morphospecies to explore the worldwide patterns in their diversity and distribution in comparison with predictions of the Ubiquity model (UM) and Moderate Endemicity model (MEM). The number of known HF morphospecies was limited (even when considering the rates of descriptions), and the local-to-global diversity ratio was relatively high (10-25%). Regional diversity was highly correlated with the investigative effort, indicating considerable under-exploration. Regional endemics were few (not over 19% of total richness), and many morphospecies were widespread or even cosmopolitan. No obvious latitudinal trend in HF diversity was detected. By species composition, the regions were distinctly arranged into three groups according to cold, temperate and warm waters, but not in accordance with geographical distances. This distribution pattern was most likely explained by contemporary climate (temperature) but did not suggest clear geographical barriers for dispersal. Therefore, the HF are less concordant with the MEM predictions but closer to the UM than other (larger) protists. Molecular studies reveal significantly higher HF diversity; the distributional patterns obtained from genetic- and morphology-based data, however, complement but not generally contradict each other.

Testate amoeba transfer function performance along localised hydrological gradients.

Testate amoeba transfer functions are widely used for reconstruction of palaeo-hydrological regime in peatlands. However, the limitations of this approach have become apparent with increasing attention to validation and assessing sources of uncertainty. This paper investigates effects of peatland type and sampling depth on the performance of a transfer function using an independent test-set from four Sphagnum-dominated sites in European Russia (Penza Region). We focus on transfer function performance along localised hydrological gradients, which is a useful analogue for predictive ability through time. The performance of the transfer function with the independent test-set was generally weaker than for the leave-one-out or bootstrap cross-validations. However, the transfer function was robust for the reconstruction of relative changes in water-table depth, provided the presence of good modern analogues and overlap in water-table depth ranges. When applied to subsurface samples, the performance of the transfer function was reduced due to selective decomposition, the presence of deep-dwelling taxa or vertical transfer of shells. Our results stress the importance of thorough testing of transfer functions, and highlight the role of taphonomic processes in determining results. Further studies of stratification, taxonomy and taphonomy of testate amoebae will be needed to improve the robustness of transfer function output.

Additive partitioning of testate amoeba species diversity across habitat hierarchy within the pristine southern taiga landscape (Pechora-Ilych Biosphere Reserve, Russia).

In order to better understand the distribution patterns of terrestrial eukaryotic microbes and the factors governing them, we studied the diversity partitioning of soil testate amoebae across levels of spatially nested habitat hierarchy in the largest European old-growth dark coniferous forest (Pechora-Ilych Biosphere Reserve; Komi Republic, Russia). The variation in testate amoeba species richness and assemblage structure was analysed in 87 samples from six biotopes in six vegetation types using an additive partitioning procedure and principal component analyses. The 80 taxa recorded represent the highest value of species richness for soil testate amoebae reported for taiga soils so far. Our results indicate that testate amoeba assemblages were highly aggregated at all levels and were mostly controlled by environmental factors rather than dispersal processes. The variation in species diversity of testate amoebae increased from the lowest to the highest hierarchical level. We conclude that, similarly to macroscopic organisms, testate amoeba species richness and community structure are primarily controlled by environmental conditions within the landscape and suggest that metacommunity dynamics of free-living microorganisms are driven by species sorting and/or mass effect processes.