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The results of the first study of the species diversity of myxomycetes of the Rdeysky State Nature Reserve are presented. The 201 field specimens of sporophores belonging to 56 morphospecies from 27 genera, ten families, and six orders were collected from September 30 to October 5, 2020. Fifty-two species of these were new for the Novgorod Region. The most common species at the reserve were Arcyria affinis, Hemitrichia calyculata, Lycogala epidendrum, Metatrichia vesparia, Physarum album, Trichia decipiens, and T. varia. Additionally, detailed morphological descriptions of two rare species Amaurochaete trechispora and Trichia crateriformis are given.

Myxomycetes are terrestrial protists with many presumably cosmopolitan species dispersing via airborne spores. A truly cosmopolitan species would suffer from outbreeding depression hampering local adaptation, while locally adapted species with limited distribution would be at a higher risk of extinction in changing environments. Here, we investigate intraspecific genetic diversity and phylogeography of Physarum albescens over the entire Northern Hemisphere. We sequenced 324 field collections of fruit bodies for 1-3 genetic markers (SSU, EF1A, COI) and analysed 98 specimens with genotyping by sequencing. The structure of the three-gene phylogeny, SNP-based phylogeny, phylogenetic networks, and the observed recombination pattern of three independently inherited gene markers can be best explained by the presence of at least 18 reproductively isolated groups, which can be seen as cryptic species. In all intensively sampled regions and in many localities, members of several phylogroups coexisted. Some phylogroups were found to be abundant in only one region and completely absent in other well-studied regions, and thus may represent regional endemics. Our results demonstrate that the widely distributed myxomycete species Ph. albescens represents a complex of at least 18 cryptic species, and some of these seem to have a limited geographical distribution. In addition, the presence of groups of presumably clonal specimens suggests that sexual and asexual reproduction coexist in natural populations of myxomycetes.

The reliability of evolutionary reconstructions based on the fossil record critically depends on our knowledge of the factors affecting the fossilization of soft‐bodied organisms. Despite considerable research effort, these factors are still poorly understood. In order to elucidate the main prerequisites for the preservation of soft‐bodied organisms, we conducted long‐term (1–5 years) taphonomic experiments with the model crustacean Artemia salina buried in five different sediments. The subsequent analysis of the carcasses and sediments revealed that, in our experimental settings, better preservation was associated with the fast deposition of aluminum and silicon on organic tissues. Other elements such as calcium, magnesium, and iron, which can also accumulate quickly on the carcasses, appear to be much less efficient in preventing decay. Next, we asked if the carcasses of uni‐ and multicellular organisms differ in their ability to accumulate aluminum ions on their surface. The experiments with the flagellate Euglena gracilis and the sponge Spongilla lacustris showed that aluminum ions are more readily deposited onto a multicellular body. This was further confirmed by the experiments with uni‐ and multicellular stages of the social ameba Dictyostelium discoideum. The results lead us to speculate that the evolution of cell adhesion molecules, which provide efficient cell–cell and cell–substrate binding, probably can explain the rich fossil record of soft‐bodied animals, the comparatively poor fossil record of nonskeletal unicellular eukaryotes, and the explosive emergence of the Cambrian diversity of soft‐bodied fossils., We present the results of long‐term (1–5 years) taphonomic experiments with Artemia salina buried in different sediments. The results imply that fossil preservation of soft‐bodied organisms depends critically on fast deposition of Al and Si ions and that the evolution of cell adhesion molecules in the early multicellular organisms probably played an important role in the sudden appearance of diverse fossil record of multicellular soft‐bodied organisms around the Precambrian/Cambrian boundary.

Physarum spectabile is reported from the Central Forest State Nature Biosphere Reserve (Nelidovsky district, Tver region), new to Russia. The short description of ecology and distribution of this rare species is provided. The morphology of the fruit bodies (sporocarps) of the species was examined by light microscopy and scanning electron microscopy (SEM), and images of relevant details are included.