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.     

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.     

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.     

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.     

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.     

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.     

Graphical Presentation of the African Tardigrade FaunaUsing GIS with the Description of Isohypsibius malawiensis sp. n. (Eutardigrada: Hypsibiidae) from Lake Malawi

The tardigrade fauna of the African continent is reviewed and presented graphically using Worldmap, a Geographical Information System (GIS) developed for exploring geographical diversity patterns in large biological datasets. References to the African tardigrade fauna have been gathered from published literature and supplemented with unpublished species information from the collection of Prof. Reinhardt M. Kristensen (RMK), Zoological Museum, University of Copenhagen. 156 species belonging to 36 genera of tardigrades are present. They consist of 105 eutardigrade species and 51 heterotardigrade species, of which 42 species are semiterrestrial and 9 species are marine. The presence of tardigrades are reported from 20 countries, but of these 9 are represented by a single reference. Marine tardigrades in particular have been neglected, with only a single report from the shores of the African continent. Data from the RMK collection of samples from Egypt is included in the analysis.

The scattered and sparse knowledge of the African tardigrade distribution makes general conclusions difficult, but emphasises the large regions which require further investigation. The current distribution patterns corresponds with easy accessible or ‘tourist’ locations. Regions where GIS could be used to illustrate ecological preferences are also pointed out by the analysis.

Isohypsibius malawiensis sp. n. is described from Lake Malawi. It has a smooth body surface and lacks eyes. The heteronych claws are without lunulae, but below the claws a double arched cuticular bar is present. The dorsal and ventral apophyses of the buccal tube have a large drop-shaped swelling. The first macroplacoid is the largest followed by the second, which is only slightly larger than the third; microplacoid is absent. Males are smaller than females. Females lay only one to two very large eggs in the exuvium. The Malpighian tubules are clover-shaped. The new species is interstitial in coarse sediment and no other tardigrade species were present.     

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.     

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.     

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.     

Trehalose and anhydrobiosis in tardigrades--evidence for divergence in responses to dehydration

To withstand desiccation, many invertebrates such as rotifers, nematodes and tardigrades enter a state known as anhydrobiosis, which is thought to require accumulation of compatible osmolytes, such as the non-reducing disaccharide trehalose to protect against dehydration damage. The trehalose levels of eight tardigrade species comprising Heterotardigrada and Eutardigrada were observed in five different states of hydration and dehydration. Although many species accumulate trehalose during dehydration, the data revealed significant differences between the species. Although trehalose accumulation was found in species of the order Parachela (Eutardigrada), it was not possible to detect any trehalose in the species Milnesium tardigradum and no change in the trehalose level has been observed in any species of Heterotardigrada so far investigated. These results expand our current understanding of anhydrobiosis in tardigrades and, for the first time, demonstrate the accumulation of trehalose in developing tardigrade embryos, which have been shown to have a high level of desiccation tolerance.     

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.     

Somatic musculature of Tardigrada: phylogenetic signal and metameric patterns

Although studies describing molecular‐based phylogenies within tardigrades are now frequently being published, this is not the case for studies combining molecular and morphological characters. Tardigrade phylogeny is still based, from a morphological point of view, almost exclusively on chitinous structures and little attention has been given to detecting and using novel morphological data. Consequently, we analysed the musculature of seven tardigrade species belonging to the main phyletic lines by confocal laser scanning microscopy and compared these morphological results with new molecular analyses (18S+28S rRNA genes). Finally, we analysed all the data with a total evidence approach. A consilience in the phylogenetic relationships among orders and superfamilies of tardigrades was obtained among the evolutionary trees obtained from morphological, molecular and total evidence approaches. Comparative analysis on the musculature allowed the identification of serial homologies and repeated metameric patterns along the longitudinal animal body axis. A phenomenon of mosaic evolution was detected in musculature anatomy, as dorsal musculature was found to be highly modified with respect to the other body muscle groups, probably related to the evolution of dorsal cuticular plates. An understanding of tardigrade musculature anatomy will give fundamental information to understand the evolution of segmental pattern within Panarthropoda. © 2013 The Linnean Society of London     

Tardigrades of Louisiana and Arkansas, United States of America

The distribution of tardigrades in the states of the southern United States is poorly known. There are no published records from the state of Louisiana, while in Arkansas only one species has been reported. Samples of mosses and lichens from trees and rocks were collected from three sites in central and southern Louisiana and six sites in western Arkansas. Leaf litter samples were collected from one site in Louisiana. Nine species of tardigrade were found in Louisiana and 22 in Arkansas. The number of species per sample ranged from one to six.     

A Large-scale, Multihabitat Inventory of the Phylum Tardigrada in the Great Smoky Mountains National Park, USA: A Preliminary Report

An All Taxa Biodiversity Inventory (ATBI) is underway in the Great Smoky Mountains National Park (GSMNP), with the goal of attempting to identify all species of life in the 2000 km² park. The GSMNP is a hotbed of biodiversity, a U.N. Biosphere Reserve, and one of the largest protected, deciduous forests in the temperate world. We have completed two field seasons of work on the tardigrades in the park (2001–2002). As of July 2003, we have collected 420 samples from soil/decomposed leaf litter, lichens and mosses on trees, and stream sediment and periphyton. A few samples from caves, bird nests, and lichens/mosses on rocks were also collected. Samples were taken from within permanent plots established for the ATBI, representing the major biological communities of the GSMNP. Tardigrades were extracted from samples using centrifugation with Ludox AM™, individually mounted on microscope slides in Hoyer’s medium, and studied with phase contrast and DIC microscopy. We have examined 1524 slides from 60 samples as of July 2003. Prior to our work, only three species of tardigrades had been previously reported from a few samples in the park. We have now recorded 42 species, 8 of which we believe may be new to science. Species richness estimates were calculated using EstimateS 6 software for each of the major tardigrade habitats. Overall, we predict that there are 47 to 76 species in the GSMNP, with generally similar species richness in soil, lichen, moss, and stream habitats. Species richness estimates were also used to determine that the number of tardigrade species was greater in mosses at breast height on trees than in mosses at the base of trees.