Tardigrade Fauna of the Region between Oka and Volga Rivers (Russia) and Patterns of their Distribution in Substrates and Habitats

The region between the Oka and Volga rivers has been largely neglected with respect to tardigrade biodiversity. In the present study a total of 21 species from 7 genera, 3 families, 2 orders and only 1 class of tardigrades were present, and some of their ecological preferences were noted. The tardigrades in the studied region were mainly cosmopolitan. Eurytopic, hygrophilic and xerophilic species were common while obligate freshwater species were not found. There is a marked similarity in the tardigrade fauna within similar habitats from different locations within the region.     

Preliminary Studies of the Tardigrade Fauna of the Faroe Bank

Four cruises to the Faroe Bank have collected bottom samples for qualitative analysis of the meiofauna. The preliminary results show a very rich tardigrade fauna, with a large proportion of species new to science. At present 35 species of tardigrades belonging to 4 families (6 sub-families) have been found, of these are 22 new to science (63%). The 35 species comprise more than 20% of all known marine tardigrades. Halechiniscidae is represented by 30 species (1 Euclavarctinae, 11 Styraconyxinae, 12 Tanarctinae, 3 Halechiniscinae, 2 Florarctinae and 1Dipodarctinae). This family comprises 87.87% of the specimens sorted out so far. Specimens from the subfamilies Tanarctinae (46.63%) and Styraconyxinae (31.54%) are dominating. Batillipedidae is represented with 3species (8.63% of the specimens) and Coronarctidae (1.89%) and Stygarctidae (1.61%) with a single species each. Samples with similar sediment from 104—260 m depth have similar species distribution in the families. This implicates that the sediment is the key factor involved in the species distribution and that depth is less important. The calcareous sediment is a unique substrate and the tardigrade fauna of the Faroe Bank can be compared with that of sub-tropical and tropical coralline sand. The composition of species exhibits a strong taxonomic affinity with the tardigrade fauna from more southern latitudes, i.e. the Mediterranean Sea and the south-eastern coast of USA.     

Factors influencing the distribution of aquatic plant communities in Irish canals

Terrestrial tardigrades are often found in the lichens and mosses growing on trees and rocks. The assertion that tardigrades in these habitats are very patchy in their distribution has rarely been backed by quantitative sampling. This study assesses spatial variability in tardigrade populations inhabiting small patches (0.1 cm² to over 5 cm²) of moss and lichen on trees and rocks at three sites in the United States of America. Tardigrades were collected from four replicate rocks in the Ouachita Mountains of Arkansas, with 30 lichen patches collected on two adjacent boulders and 20 moss patches on a second pair of boulders. In Fort Myers and in Citrus Springs, Florida, 30 lichen patches per tree were collected from two pairs of trees. The tardigrades in each sample were extracted, mounted, identified, and counted. The variation in tardigrade abundance among lichen or moss patches within rocks or trees was very high; the only consistent pattern was that very small patches usually lacked tardigrades. Tardigrade diversity and abundance also varied greatly within sites when lichens and mosses of the same species from different rocks and trees were compared (in the most extreme case one tree had numerous individuals of two tardigrade species present while the other had almost no tardigrades). The results of this quantitative sampling support the assertion that tardigrades are very patchy in distribution. Given the considerable time investment required for the quantitative processing of tardigrade samples, this high spatial variability in tardigrade diversity and abundance requires that researches testing ecological hypotheses about tardigrade abundance check variability before deciding how many samples to take.     

Population density and species composition of moss-living tardigrades in a boreo-nemoral forest

This study investigates for the first time the tardigrade fauna in a variety of different mosses from a coniferous forest and an adjacent clear-cut area in southern Sweden. Tardigrades were found in a majority of the samples. Sixteen species were recorded, of which the cosmopolitan species Macrobiotus hufelandi was the far most common. Some mosses, particularly species with "wefts" growth form, contained more tardigrades than other mosses, indicating that growth form may have an impact on tardigrade abundance. Mosses of the same species collected from a forest and from a clear-cut, respectively, did not show a general trend in the overall abundance of tardigrades, but the forest tended to contain more species. Five species of tardigrades ( Murrayon dianae, Isohypsibius sattleri, Platicrista angustata, Diphascon belgicae and Diphascon pingue ) never previously reported from Sweden were recorded.     

Micro-distribution of Soil Inhabiting Tardigrades (Tardigrada) in a Sub-alpine Coniferous Forest of Japan

Micro-distribution of soil inhabiting tardigrades was studied in a sub-alpine coniferous forest (alt. 1,840 m a. s. l.) on the eastern slope of Mt. Yatsugatake, Central Japan. Eight cylindrical soil samples were taken from the forest floor. Each sample was divided into 10 slice samples of 1 cm thick. Tardigrades were extracted from samples by Baermann funnels, identified to specific level and counted. The average number of tardigrades in the study site is 74,058/m². High densities sometimes occurred at depths greater than 5 cm. Consequently for investigating tardigrade populations, 5cm depth core sampling is insufficient in this type of habitat. Composition of the main groups of species reveals that shallow layers (1, 2 or 3 cm depth) are frequently dominated by the Diphascon-group. Macrobiotus-group species generally occurred in higher abundance in the deeper layers. It is very interesting that there are some different patterns of soil micro-distribution in tardigrade species.     

DNA taxonomy of a neglected animal phylum: an unexpected diversity of tardigrades

A molecular survey technique was used to investigate the diversity of terrestrial tardigrades from three sites within Scotland. Ribosomal small subunit sequence was used to classify specimens into molecular operational taxonomic units (MOTU). Most MOTU were identified to the generic level using digital voucher photography. Thirty-two MOTU were defined, a surprising abundance given that the documented British fauna is 68 species. Some tardigrade MOTU were shared between the two rural collection sites, but no MOTU were found in both urban and rural sites, which conflicts with models of ubiquity of meiofaunal taxa. The patterns of relatedness of MOTU were particularly intriguing, with some forming clades with low levels of divergence, suggestive of taxon flocks. Some morphological taxa contained well-separated MOTU, perhaps indicating the existence of cryptic taxa. DNA sequence-based MOTU proved to be a revealing method for meiofaunal diversity studies.     

Appearance of males in a thelytokous strain of Milnesium cf. tardigradum (Tardigrada)

Tardigrades are generally gonochoristic. Many moss-dwelling species propagate by parthenogenesis, but heterogony has not yet been found. Milnesium tardigradum, a carnivorous tardigrade, also has both sexes, but males are usually rare and many populations appear to have only parthenogenetic reproduction. Since 2000, I have maintained a thelytokous strain of Milnesium cf. tardigradum that originated from one female. Individuals of this strain were thought to be all females, but here I report that males have emerged in this strain at a very low frequency. This is the first report of the appearance of males in parthenogenetic tardigrades. On the first pair of legs of some individuals, I observed the modified claws characteristic of males of this species. It is unknown whether these males can actually function in sexual reproduction; however, they might allow some possibility of genetic exchange among clonal populations. No environmental factors that generate males were determined.     

Interspecific Association and Substrate Specificity in Tardigrades from Florida, Southeastern United States

The distribution of terrestrial tardigrades in the Gulf Coast states of the United States is poorly known. Only one species has been reported in Florida. In this study moss, liverwort, lichen and fern samples (47 identified species) from trees and shrubs were collected from all 67 Florida counties. These samples contained 20 species of tardigrade. All possible pairs of tardigrade species and tardigrade and substrate were tested for interspecific association. Only three significant negative and one positive interspecific association between tardigrades were detected. Evidence for substrate specificity was weak. Although some tardigrade species were significantly associated with mosses or foliose lichens in general, no significant association between a tardigrade species and a substrate species was detected.     

Tardigrades of the Australian Antarctic: Macquarie Island, sub-Antarctica

Sub-Antarctic Macquarie Island lies in the Southern Ocean between Tasmania and Antarctica and just above the Antarctic Convergence. Extensive flora and fauna samples were collected during the 1977—78 Australian Museum Expedition. Thirteen genera and 25 species of tardigrades are reported from among the 8725 specimens recovered from the 72 samples. Association between species of tardigrades and between species of tardigrades and plant species are discussed. Possible predator-prey relationships are suggested by patterns of association.     

Identification and differentiation of Heterotardigrada and Eutardigrada species by riboprinting

In the last decades, the number of known tardigrade species has considerably increased to more than 960 species with new ones being discovered every year. However, the study of tardigrade species presents a general problem which is frequently encountered during the work with invertebrates: small size and remarkable degrees of phenotypic plasticity may sometimes not permit a definite identification of the species. In this investigation we have used riboprinting, a tool to study rDNA sequence variation, in order to distinguish tardigrade species from each other. The method combines a restriction site variation approach of ribotyping with amplified DNAs. In eight investigated species of heterotardigrades and eutardigrades we have amplified the genes for the small subunit ribosomal RNA (SSU; 18S) and subsequently sequenced the genes. Virtual riboprints were used for identification of restriction sites from ten already published 18S rDNA sequences and seven new 18S rDNA sequences. On the basis of the obtained sequences, diagnostic restriction fragment patterns can be predicted with only 11 restriction enzymes. The virtual digestion confirmed the obtained restriction fragment patterns and restriction sites of all amplified and digested tardigrade DNAs. We show that the variation in positions and number of restriction sites obtained by standard restriction fragment analysis on agarose gels can be used successfully for taxonomic identification at different taxonomic levels. The simple restriction fragment analysis provides a fast and convenient method of molecular barcoding for species identification in tardigrades.     

Distribution of Tardigrades within a Moss Cushion: Do Tardigrades Migrate in Response to Changing Moisture Conditions?

The distribution of tardigrades within the layers of the cushion moss Grimmia alpicola Hedwig, 1801 was investigated. The aim of this study was to determine the tardigrade species present within the moss layers during both wet and dry periods and to determine if migration occurred in response to changing moisture conditions. Samples of the moss were removed from concrete caps on brick fence posts before and after rainfall and separated into two sections (top and bottom). The tardigrades from each layer and moisture condition were identified to species. Data for each species were statistically analyzed with a two-way analysis of variance (ANOVA) to compare the numbers of individuals present in the top and bottom layers of the moss under both wet and dry conditions.

Five tardigrade species were identified, including two species new to science: Macrobiotus sp. n.; Milnesium tardigradum Doyère, 1840; Echiniscus viridissimus Peterfi, 1956; Echiniscus perviridis Ramazzotti, 1959; and Echiniscus sp. n. The new species will be described in a forthcoming paper. No significant differences were found in the numbers of individuals of four of the five species in each layer within the moss or for each moisture condition. Only one species, E. viridissimus, was significantly more frequent in the top layer of the moss, regardless of moisture condition.

Migration within the moss cushion was not detected in any of these five species as a result of changes in moisture conditions. In xeric moss species, it may not be beneficial for tardigrades to migrate to avoid desiccation. Instead, they apparently undergo anhydrobiosis in both the top and bottom layers of the moss cushion.     

Ecological Distribution and Community Analysis of Tardigrada from Choccolocco Creek, Alabama

A seasonal survey of tardigrade populations in the riparian zone of the Choccolocco Creek, Alabama, was undertaken from August 1994 through December 1995. Six sites within the riparian zone were sampled in different portions of the creek. At each site, 3 trees with cryptogams were sampled six times during survey period. From a total of 108 samples, 1,588 tardigrades were extracted and individually mounted on slides in Hoyer's medium. The community was dominated (86%) by specimens in the genus Macrobiotus. One species of Echiniscus was new to science and will be described in a separate paper. No significant difference was found between tardigrade occurrence (total number of individuals) and season, moss genera, or tree species. However, there was a significant relationship between the number of tardigrades and site, indicating the need for additional replicate samples. Simpson's and Shannon-Wiener's species diversity indices indicated that species richness and evenness were low. Jaccard's and Standard's community similarity indices suggested that the communities within the riparian zone were dissimilar along Choccolocco Creek.     

The Distribution of Tardigrades Upwind and Downwindof a Missouri Coal-Burning Power Plant

Significant differences occurred in the density of tardigrades, rotifers, and nematodes and the diversity of tardigrades between collecting sites located upwind and downwind from a coal-burning power plant in Missouri. The oak tree species and lichen genera also varied in the two areas. Tardigrade and rotifer densities were greater in upwind sites, whereas nematode density was higher in downwind samples. One tardigrade species (Ramazzottius sp.) was found only at the upwind sites, and one species (Echiniscus sp.) was only in the downwind samples. In contrast, three species (Macrobiotus sp., Minibiotus sp., and Milnesium tardigradum) were found both upwind and downwind but in different densities in the two areas. The study presents baseline data for long-term monitoring of the effects of environmental factors on nematode and rotifer densities as well as tardigrade density and diversity.     

The Tardigrades of Emilia (Italy). III. Piane di Mocogno (Northern Apennines)

Samples of leaf litter, mosses and lichens were collected in a beech forest at Piane di Mocogno (Emilia, Italy), 1200 m asl. The tardigrade community of the leaf litter was similar to that found in this substrate in Italy and in the U.S.A. At Piane di Mocogno the species association within the leaf litter was different from that in mosses and lichens (which have similar fauna), confirming that very different communities characterise different substrates such as leaf litter and mosses. During this faunal analysis, six species of tardigrades were found for the first time in this area. The presence of Microhypsibius bertolanii (first record in leaf litter and in Italy) and Eohypsibius nadjae are note worthy. Ornamented eggs in an exuvium of Hypsibius cf.scabropygus were also recorded for the first time.     

First evidence of achiasmatic male meiosis in the water bears Richtersius coronifer and Macrobiotus richtersi (Eutardigrada, Macrobiotidae)

Chromosome behaviour during male meioses has been studied in two bisexual amphimictic populations of two tardigrade species, namely Richtersius coronifer and Macrobiotus richtersi (Eutardigrada, Macrobiotidae). Both bisexual populations exhibit a diploid chromosome number 2n=12 and no sex chromosomes were identified. DAPI staining and C-banding data indicate that all chromosomes of the bisexual population of R. coronifer are acrocentric. In both species, at male meiotic prophase, all six bivalent homologous chromosomes are aligned side by side along their length and show no evidence of chiasmata. However, in the oocytes of both species a chiasma is generally present in each bivalent at diplotene stage. Lack of recombination is previously unknown in tardigrades, but is a well known phenomenon in many other metazoans where it is always restricted to the heterogametic sex. In tardigrades there is no evidence of heterochromosomes, but it does not mean that in tardigrades, the heterogametic sex does not exist. The adaptive and evolutionary significance of achiasmatic meiosis is discussed.     

Soil-inhabiting Tardigrade Communities in Forests of Central Japan

This study was carried out for the purpose of detecting the relationship between soil-inhabiting tardigrade communities and environmental factors of various forests. Nine forests in the southern part of Kanagawa Prefecture, Central Japan, were selected for this study. Four vegetation types were designated; broadleaved (evergreen/deciduous), coniferous and orchard. In these sites, dry weight of leaf litter, soil pH, soil hardness, soil moisture content and porosity ratio were measured. Wet soil faunal frequencies were also described. The Baermann funnel method was adopted for collecting tardigrades, and DIC microscopy was used for specific identification. To clarify the correlation between environmental variables and tardigrade faunae, multivariate analysis was applied. The tardigrade fauna occurred as two distinct groups. The first group primarily contained Macrobiotus species. The second group contained the genus Diphascon (e.g. D. nobilei, D. patanei, D. prorsirostre). An exception to this was D. pingue, included in the former. Most of the Diphascon species were concentrated in Nebu (coniferous forest site), while, Macrobiotus species were dominant in other sites. Distinct environmental factors could not be identified, but the nematodal frequency was recognized as the main factor in forming these groups. The uniqueness of Nebu, which does not correspond to large-scaled vegetational classification, was substantiated by statistical data. Nebu’s coniferous forest apparently has created a unique environment for sustaining rare species (Diphascon species). This study concluded that forests should be evaluated not only by the macroscopic factors, such as landscape, but also by the microscopic communities, such as those including the tardigrades.