Diatoms in cryoconite holes and adjacent proglacial freshwater sediments, Nordenskiöld glacier (Spitsbergen, High Arctic)

Cryoconite holes are small, extreme habitats, widespread in the ablation zones of gla-ciers worldwide. They can provide a suitable environment for microorganisms including bacteria, cyanobacteria, algae, fungi, and invertebrates. Diatoms have been previously recovered from cryoconite holes of Greenland and of Svalbard, and recent findings from Antarctica suggest that cryoconite holes may harbor a unique diatom flora distinct from other aquatic habitats nearby. In the present study, we characterize the diatom communi-ties of Nordenskiöld glacier cryoconite holes in Billefjorden (Svalbard, Spitsbergen), and multivariate approaches were used to compare them with three freshwater localities in the immediate vicinity to investigate possible sources of the species pool. We found cryoconite holes to have similar or greater average genus-richness than adjacent lake/ ponds habitats, even though lower numbers of valves were recovered. Overall, cryoconite hole diatom communities differed significantly from those observed in lakes, suggesting that other sources actively contribute to these communities than nearby lakes alone. This further suggests that (i) diatoms present in cryoconite might not exclusively originate from aquatic habitats, but also from (semi-) terrestrial ones; and (ii) that a much wider area than the immediate surroundings should be considered as a possible source for cryoconite diatom flora

Global radiation in a rare biosphere soil diatom

Soil micro-organisms drive the global carbon and nutrient cycles that underlie essential ecosystem functions. Yet, we are only beginning to grasp the drivers of terrestrial microbial diversity and biogeography, which presents a substantial barrier to understanding community dynamics and ecosystem functioning. This is especially true for soil protists, which despite their functional significance have received comparatively less interest than their bacterial counterparts. Here, we investigate the diversification of Pinnularia borealis, a rare biosphere soil diatom species complex, using a global sampling of >800 strains. We document unprecedented high levels of species-diversity, reflecting a global radiation since the Eocene/Oligocene global cooling. Our analyses suggest diversification was largely driven by colonization of novel geographic areas and subsequent evolution in isolation. These results illuminate our understanding of how protist diversity, biogeographical patterns, and members of the rare biosphere are generated, and suggest allopatric speciation to be a powerful mechanism for diversification of micro-organisms

Polar lake microbiomes have distinct evolutionary histories

Toward the poles, life on land is increasingly dominated by microorganisms, yet the evolutionary origin of polar microbiomes remains poorly understood. Here, we use metabarcoding of Arctic, sub-Antarctic, and Antarctic lacustrine benthic microbial communities to test the hypothesis that high-latitude microbiomes are recruited from a globally dispersing species pool through environmental selection. We demonstrate that taxonomic overlap between the regions is limited within most phyla, even at higher-order taxonomic levels, with unique deep-branching phylogenetic clades being present in each region. We show that local and regional taxon richness and net diversification rate of regionally restricted taxa differ substantially between polar regions in both microeukaryotic and bacterial biota. This suggests that long-term evolutionary divergence resulting from low interhemispheric dispersal and diversification in isolation has been a prominent process shaping present-day polar lake microbiomes. Our findings illuminate the distinctive biogeography of polar lake ecosystems and underscore that conservation efforts should include their unique microbiota

Gomphonema svalbardense sp. nov., a new freshwater diatom species (Bacillariophyta) from the Arctic Region

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Diatom communities in Petuniabukta (Spitsbergen, Svalbard Archipelago): a taxonomic and (paleo)ecological approach

Diatoms are one of the most abundant algal groups in polar ecosystems, both in number of specimens as in number of species. Their characteristic silica valve and the significant responses to changes in their physical and chemical environment, make them excellent bio-indicators used in applied environmental and paleoecological studies. Despite this, the species composition and ecological preferences of High Arctic diatom communities are poorly known, mainly due to historic force-fitting and incorrect species identifications. The diatom flora of Svalbard in particular is little studied and most studies published so far are very concise. Here we studied the freshwater littoral diatom flora of Petuniabukta (Spitsbergen) on a spatial and temporal scale in order to reduce the taxonomic and ecological uncertainty when applying diatoms as (paleo)environmental indicators in the Arctic. For the spatial scale, the diatom flora of 53 freshwater lakes was analysed using light and scanning electron microscopy. More than 300 taxa belonging to 59 genera have been found, of which one third could not be identified below genus level. Two new species, Gomphonema svalbardense and Achnanthidium petuniabuktianum, have recently been described as new to science and several other taxa are in need of a formal description. Cluster and ordination analyses allowed separating the diatom communities in four main assemblages which were explained by differences in environmental characteristics, such as the presence of streams, mosses and glaciers. For the temporal scale, the diatom succession in a ~6000 year old sediment core from Garmaksla Lake was studied. Changes in the relative abundances of the two dominating taxa, Staurosira venter and Amphora affinis, suggest subsequent periods of warming and cooling. Unprecedented changes in the top layers of the core are attributed to climate warming as result of the end of the Little Ice Age, ~100–150 years ago, and, more recently, human induced environmental changes. In conclusion, the high number of unidentified taxa in this study indicates that a profound revision of the Arctic diatom flora is highly desired, not only to improve our fundamental knowledge concerning the diversity, ecology and biogeography of Arctic diatoms, but also to advance applied (paleo)ecological studies

A time-calibrated multi-gene phylogeny provides insights into the evolution, taxonomy and DNA barcoding of the Pinnularia gibba group (Bacillariophyta )

Many diatom groups are known for widespread (pseudo)cryptic species diversity and Pinnularia gibba group is one of them. Recently, KoLLAR et al. (2019) delimited species within the group by means of a polyphasic approach, providing an evidence for the existence of fifteen species. In order to further guide the systematic revision of the group, the present study focuses on the evolution and morphology of the P. gibba group. Using representatives of the fifteen species we used fossils to constrain and calibrate a multi-gene species-level phylogeny. Although many species are morphologically highly similar, significant differences in cell size were detected in different sections of the tree, suggestive of ongoing morphological differentiation. We further used the phylogenetic analysis to assess marker resolution for DNA barcoding, showing that the proposed diatom barcode markers rbcL and V4 SSU rDNA can distinguish closely related (pseudo)cryptic species of the group

Achnanthidium petuniabuktianum sp. nov. (Achnanthidiaceae, Bacillariophyta), a new representative of the A. pyrenaicum group from Spitsbergen (Svalbard Archipelago, High Arctic)

During a survey of the freshwater littoral diatom flora from lakes and ponds in the region of Petuniabukta on Spitsbergen (Svalbard Archipelago, High Arctic region), a new Achnanthidium species, A. petuniabuktianum sp. nov., has been recorded. Achnanthidium petuniabuktianum is a new representative of the A. pyrenaicum group as evidenced by its curved distal raphe fissures. The present paper describes in detail the morphology of A. petuniabuktianum based on light and scanning electron microscopy. The new taxon is characterized in having linear valves with parallel margins and broadly rounded, never protracted apices and a characteristic—in light microscopy hardly discernible—striation pattern consisting of very short striae composed of one or two small, always slit-like areolae. Based on current results, Achnanthidium petuniabuktianum is a benthic taxon occurring in epilithic and epiphytic habitats in the littoral zones of freshwater lakes and ponds