Yuri K. Novozhilov

Myxomycete diversity and distribution from the fossil record to the present

The myxomycetes (plasmodial slime molds or myxogastrids) are a group of eukaryotic microorganisms usually present and sometimes abundant in terrestrial ecosystems. Evidence from molecular studies suggests that the myxomycetes have a significant evolutionary history. However, due to the fragile nature of the fruiting body, fossil records of the group are exceedingly rare. Although most myxomycetes are thought to have very large distributional ranges and many species appear to be cosmopolitan or nearly so, results from recent studies have provided evidence that spatial distribution patterns of these organisms can be successfully related to (1) differences in climate and/or vegetation on a global scale and (2) the ecological differences that exist for particular habitats on a local scale. A detailed examination of the global distribution of four examples (Barbeyella minutissima, Ceratiomyxa morchella, Leocarpus fragilis and Protophysarum phloiogenum) demonstrates that these species have recognizable distribution patterns in spite of the theoretical ability of their spores to bridge continents.

Genetic Structure of Two Protist Species (Myxogastria, Amoebozoa) Suggests Asexual Reproduction in Sexual Amoebae

Plasmodial slime molds (Myxogastria or Myxomycetes) are common and widespread unicellular organisms that are commonly assumed to have a sexual life cycle culminating with the formation of often macroscopic fruiting bodies that efficiently disseminate spores. However, laboratory studies based on mating compatibility revealed the coexistence of asexual as well as sexual strains. To test this hypothesis in natural populations, we investigated the genetic variability of two species of the genus Lamproderma. Detailed ecological relevés were carried out in 2007 and 2009 in several deep ravines in the Elbsandsteingebirge (Saxony, south-eastern Germany). Morphological characters of 93 specimens of Lamproderma were recorded and genetic analyses, based on the small subunit ribosomal gene, the internal transcribed spacer 1 and partial elongation factor 1α sequences were carried out for 52 specimens. Genetic analyses showed the existence of two major clades, each composed of several discrete lineages. Most of these lineages were composed of several identical sequences (SSU, ITS 1 and EF-1α) which is explained best by an asexual mode of reproduction. Detrended Correspondence Analysis of morphological characters revealed two morphospecies that corresponded to the two major clades, except for one genotype (Lc6), thus challenging the morphospecies concept. Genetic patterns were not related to the geographical distribution: specimens belonging to the same genotype were found in distinct ravines, suggesting effective long-distance dispersal via spores, except for the Lc6 genotype which was found only in one ravine. Implications for the morphological and biological species concept are discussed.

Myxomycete biodiversity of the Colorado Plateau

A rapid biodiversity assessment for myxomycetes (plasmodial slime moulds) was carried out during a two-week field trip to the Colorado Plateau (western U.S.A.). Due to the very arid climate of the region, the moist chamber culture technique formed a major part of the survey. A total of 1165 records belonging to 93 species and 1 variety from 27 genera was collected from the 433 moist chamber cultures prepared with the bark surface of living plants, litter and weathered dung of herbivorous animals. Only 31 specimens of 16 wood-inhabiting species were collected in the field, mainly at higher elevations. Subsequent moist chamber cultures produced numerous bark-inhabiting species that are usually considered to be rare, including Echinostelium coelocephalum, Protophysarum phloiogenum, and Macbrideola declinata. The most common litter-inhabiting species were Didymium mexicanum and Badhamia melanospora (mainly on decaying parts of Opuntia spp. and Agave spp.); the most abundant coprophilous species were Badhamia cf. apiculospora, Fuligo cinerea, Perichaena liceoides, and Licea tenera. Both, species richness and diversity, increase from sagebrush desert to pine-juniper open woodland and pine-oak woodland. The myxomycete biota of the Colorado Plateau displays a high level of similarity to those of other arid regions of the world (mean coefficient of community Cs = 0.67), differing considerably from temperate (mean Cs = 0.34), boreal (mean Cs = 0.49) and tropical biotas (mean Cs = 0.42).

Ecology and world distribution of Barbeyella minutissima(Myxomycetes).

On the basis of all accessible records from the literature and our own field observations and collections, the ecology of the rare myxomycete Barbeyella minutissima is described. Analysis of these data, derived mainly from the Northern Ammergauer Alps (Germany) and the Appalachian Mountains (USA: West Virginia, North Carolina), permit the microhabitat requirements of this myxomycete and its ecological associations with other myxomycetes and bryophytes to be elucidated in some detail. Barbeyella minutissima appears to have a distribution centred in montane spruce-fir forests, where it is regularly associated with three other species of myxomycetes - Colloderma oculatum, Lamproderma columbinum, and Lepidoderma tigrinum. Several leafy liverworts are associated with Barbeyella. Particularly noteworthy is Nowellia curvifolia, which seems to be an indicator organism for this myxomycete. A world distribution map of Barbeyella minutissima is provided, along with conclusions relating to the putative range of the species.

Two new species of Perichaena (Myxomycetes) from arid areas of Russia and Kazakhstan

Two new myxomycete species from dry steppe and desert communities of the Caspian Lowland (Russia) and central Kazakhstan are described and illustrated. They are placed tentatively within genus Perichaena, which does include species with a reduced capillitium and single-layered peridium. Both species were found repeatedly in moist chamber cultures; P. heterospinispora appeared on leaf litter and twigs, whereas P. polygonospora occurred on leaf litter and weathered dung of rodents. Both species have spore ornamentation that is unique for members of genera Licea and Perichaena. The spore ornamentation of the first species includes scattered large, pyramid-like spines 0.9–1.2 μ m high that sometimes have enlarged ends. Among these spines the spore surface is covered by evenly and densely distributed warts that are visible only by SEM. The second species is characterized by angular spores with a coarse network of rounded ridges. The areas among these ridges bear scattered composite warts 0.3–0.5 μ m high that sometimes coalesce to form clusters but more often are distributed evenly and densely and are visible only by SEM. The stability of the taxonomic characters of both species was confirmed by several collections from different regions obtained in 2 y. The morphology of the fructifications of the two myxomycetes was examined with both scanning electron and light microscopy, and micrographs of all relevant features are presented.

Description, culture and phylogenetic position of a new xerotolerant species of Physarum

A new widespread myxomycete species, Physarum pseudonotabile, inhabiting the arid regions of the Eurasia, South and North America is described and illustrated. Tentatively assigned to Ph. notabile T. Macbr., a phylogeny based on the small ribosomal subunit (SSU) and elongation factor 1 alpha (EF1a) genes placed the new species in a clade far from Ph. notabile. Ph. pseudonotabile was found to be frequent in surveys based on the moist chamber culture technique with samples of litter, bark and herbivore dung collected in dry steppe and deserts of the Caspian lowland (Russia), Kazakhstan, Mongolia, China, Spain, Argentina and USA. The main morphological difference between Ph. pseudonotabile and Ph. notabile lies in spore ornamentation. Spores of the former species display irregularly distributed verrucae, whereas the latter species possesses spores with dense and regularly arranged spinulae. In addition, the ecological preferences of the two species differ. Ph. pseudonotabile inhabits the bark of living plants and ground litter in arid regions, whereas Ph. notabile is found on coarse woody debris in boreal and temperate forests. Although the new species appears to be closest to Ph. notabile morphologically, the phylogenetic analysis reveals Ph. pusillum and Ph. nivale as the closest relatives. In addition, the molecular investigations revealed a considerable amount of hidden diversity within species of Physarum with gray lime flakes. Currently we have only sufficient material to assess the morphological variation of Ph. pseudonotabile but expect that more taxa within this clade may emerge within studies combining morphological and molecular analyses.

What an Intron May Tell: Several Sexual Biospecies Coexist in Meriderma spp. (Myxomycetes).

Specimens of the snowbank myxomycete Meriderma atrosporum agg. from five European mountain ranges were sequenced for parts of the nuclear small subunit ribosomal RNA gene (SSU) and the protein elongation factor 1 alpha gene (EF1A). A phylogeny of the EF1A gene, including a very variable spliceosomal intron, resulted in seven phylogroups, and this topology was confirmed by SSU sequences. Two thirds of all specimens were heterozygous for the EF1A gene, and the two haplotypes of these specimens occurred always in the same phylogroup. Except for two cases in closely related phylogroups all ribotypes were as well limited to one phylogroup. This pattern is consistent with the assumption of reproductively isolated sexual biospecies. Numbers of EF1A-haplotypes shared between mountain ranges correlate with geographical distance, suggesting relative isolation but occasional long-distance dispersal by spores. Most subpopulations (divided by putative biospecies and mountain ranges) were in Hardy-Weinberg equilibrium. A simulation assuming panmixis within but not in between subpopulations suggested that similar numbers of shared genotypes can be created by chance through sexual reproduction alone. Our results support the biospecies concept, derived from experiments with cultivable members of the Physarales. We discuss the results on the background of possible reproductive options in myxomycetes.

Phylogenetic position of the enigmatic myxomycete genus Kelleromyxa revealed by SSU rDNA sequences

The coprophilous myxomycete Kelleromyxa fimicola (Dearn. & Bisby) Eliasson was first described in 1929 as Licea fimicola Dearn. & Bisby. Based on the superficial resemblance of its sporocarps to those of Licea biforis, the species was placed within the Liceales, an order assigned by molecular phylogenies to the bright-spored clade of myxomycetes. However, detailed studies of the morphology and life cycle of K. fimicola revealed several characters of the dark-spored order Physarales. To elucidate the systematic position of Kelleromyxa, we obtained three partial and one complete sequence of the SSU rDNA, which demonstrated a clear relationship of K. fimicola to the order Physarales. However, the obtained sequences are not closely related to any of the two known families of Physarales, supporting the erection of a monotypic family for this species. Along with morphological observations, our data support the exclusion of K. fimicola from the order Liceales and placement among the order Physarales within the dark-spored clade of myxomycetes.

Stable isotope composition (δ13C and δ15N values) of slime molds: placing bacterivorous soil protozoans in the food web context

RATIONALE Data on the bulk stable isotope composition of soil bacteria and bacterivorous soil animals are required to estimate the nutrient and energy fluxes via bacterial channels within detrital food webs. We measured the isotopic composition of slime molds (Myxogastria, Amoebozoa), a group of soil protozoans forming macroscopic spore-bearing fruiting bodies. An analysis of largely bacterivorous slime molds can provide information on the bulk stable isotope composition of soil bacteria. METHODS Fruiting bodies of slime molds were collected in a monsoon tropical forest of Cat Tien National Park, Vietnam, and analyzed by continuous-flow isotope ratio mass spectrometry. Prior to stable isotope analysis, carbonates were removed from a subset of samples by acidification. To estimate the trophic position of slime molds, their δ(13) C and δ(15) N values were compared with those of plant debris, soil, microbial destructors (litter-decomposing, humus-decomposing, and ectomycorrhizal fungi) and members of higher trophic levels (oribatid mites, termites, predatory macroinvertebrates). RESULTS Eight species of slime molds represented by at least three independent samples were 3-6‰ enriched in (13) C and (15) N relative to plant litter. A small but significant difference in the δ(13) C and δ(15) N values suggests that different species of myxomycetes can differ in feeding behavior. The slime molds were enriched in (15) N compared with litter-decomposing fungi, and depleted in (15) N compared with mycorrhizal or humus-decomposing fungi. Slime mold sporocarps and plasmodia largely overlapped with oribatid mites in the isotopic bi-plot, but were depleted in (15) N compared with predatory invertebrates and humiphagous termites. CONCLUSIONS A comparison with reference groups of soil organisms suggests strong trophic links of slime molds to saprotrophic microorganisms which decompose plant litter, but not to humus-decomposing microorganisms or to mycorrhizal fungi. Under the assumption that slime molds are primarily feeding on bacteria, the isotopic similarity of slime molds and mycophagous soil animals indicates that saprotrophic soil bacteria and fungi are similar in bulk isotopic composition.

Ecology of sandstone ravine myxomycetes from Saxonian Switzerland (Germany)

We describe the ecology of a highly specialized community of ravine myxomycetes from sandstone gorges of the Saxonian Switzerland region (near Dresden, Germany). Five taxa, Colloderma robustum, Diderma ochraceum, Lamproderma columbinum, L. puncticulatum agg. and Lepidoderma tigrinum, account for 87% of all records. Colloderma robustum and Diderma lucidum are new records for Germany; Diderma ochraceum was known from a few collections only. A total of 127 small-scale vegetation releves showed that the community occurs only in deep and narrow ravines (mean horizon openness 4.9%) on nearly vertical rocks (mean inclination 79°), and preferentially in northern exposition (42% of all releves). Substrate pH is very acidic (mean 3.35). At the fructification time of the myxomycetes (beginning of October) the microclimate is very constant with temperatures around 10°C and nearly 100% relative humidity around the day. Beside green algae (associated with 100% of all myxomycete records, most common was Coccomyxa confluens (Kutz.) Fott s.l.) the bryophytes Mylia taylorii (64%), Dicranodontium denudatum (59%), Tetraphis pellucida (50%) and Diplophyllum albicans (40%) were of high indicator value for this community. Low values for niche width of the five more common myxomycete species reflect the high degree of specialization for the community as a whole, whereas niche overlap between species is high. Low values for the Cole index of association can be interpreted as competition between species or, more likely, reflect the relative rarity of fruiting colonies.