Tardigrade Populations Research Articles

An experimental study on tolerance to hypoxia in tardigrades.

Introduction: Tardigrades are small aquatic invertebrates with well documented tolerance to several environmental stresses, including desiccation, low temperature, and radiation, and an ability to survive long periods in a cryptobiotic state under arrested metabolism. Many tardigrade populations live in habitats where temporary exposure to hypoxia is expected, e.g., benthic layers or substrates that regularly undergo desiccation, but tolerance to hypoxia has so far not been thoroughly investigated in tardigrades. Method: We studied the response to exposure for hypoxia (<1ppm) during 1-24h in two tardigrade species, Richtersius cf. coronifer and Hypsibius exemplaris. The animals were exposed to hypoxia in their hydrated active state. Results: Survival was high in both species after the shortest exposures to hypoxia but tended to decline with longer exposures, with almost complete failure to recover after 24h in hypoxia. R. cf. coronifer tended to be more tolerant than H. exemplaris. When oxygen level was gradually reduced from 8 to 1ppm, behavioral responses in terms of irregular body movements were first observed at 3-4ppm. Discussion: The study shows that both limno-terrestrial and freshwater tardigrades are able to recover after exposure to severe hypoxia, but only exposure for relatively short periods of time. It also indicates that tardigrade species have different sensitivity and response patterns to exposure to hypoxia. These results will hopefully encourage more studies on how tardigrades are affected by and respond to hypoxic conditions.

Negative impact of freeze–thaw cycles on the survival of tardigrades

Global warming effects in temperate and polar regions include higher average temperatures and a decrease in snow cover, which together lead to an increase in the number of freeze–thaw cycles (FTC). These changes could affect the fitness of both terrestrial and aquatic species. In this study, we tested how tardigrades, ubiquitous microscopic invertebrates, face FTC. Tardigrades are amongst the most resistant animals to unfavorable conditions, including long and deep freezing periods, and are an emerging model group for invertebrate ecology and evolution. We used 12 populations of tardigrades, representing different families within order Parachela, inhabiting different ecosystems (glaciers, snow, terrestrial, aquatic), found in various substrates (mosses, sediments in lakes, cryoconite on glaciers, and snow), and originating from different latitudes and altitudes. We estimated the number of cycles required to kill 50% of individuals and tested for its association with ecological characteristics of the natural habitat (e.g., number of months with predicted FTC), while accounting for phylogeny. The most resistant tardigrades to FTC were the ones from mountain areas and glaciers. The estimated number of cycles required to kill 50% of individuals was the highest for mountainous species inhabiting rock pools and cryoconite holes on glaciers (30 and 14 FTC, respectively). Tardigrades from lowlands were the most sensitive to changes, with 50% of individuals dying after three FTC, while lacustrine and subtropical tardigrades required only one FTC to reach 50% mortality. Our study shows that the response to recurrent freezing stress is taxon dependent and related to the local environmental conditions. The predicted increase of FTC cycles will negatively impact tardigrade populations. Considering the abundance and various trophic roles of tardigrades, reduction in population sizes or the disappearance of some fragile species could affect the functioning of both aquatic and terrestrial ecosystems. Tardigrades are candidate indicators of how freeze–thaw cycles impact ubiquitous microscopic metazoans with similar physiological capabilities.

Defining the viability of tardigrades with a molecular sensor related to death.

The design of experimental protocols that use animal models to assess the impact of a stress on a population or to determine the life span expectancy impact can be time-consuming due to the need for direct observations of dead and living animals. These experiments are usually based on the detectable activity of animals such as food intake or mobility and can sometimes produce either under- or overestimated results. The tardigrade Hypsibius exemplaris is an emerging model for the evolutionary biology of the tardigrade phylum because of its convenient laboratory breeding and the recent introduction of new molecular tools. In this report, we describe the use of a new fluorescent dye that can specifically stain dead tardigrades. Furthermore, we also monitored the absence of a toxic side effect of the death-linked fluorescent dye on tardigrade populations. Finally, we conclude that tardigrade experiments that require survival counting of the Hypsibius exemplaris species can be greatly improved by using this technique in order to limit underestimation of alive animals.

Evaluation of extraction methods for quantitative analysis of tardigrade populations in soil and leaf litter

Accurate quantitative analysis of soil tardigrades depends on a relevant extraction method. Over the years, a number of different methods have been used, but the efficiency of these methods has rarely been evaluated for soil and leaf litter tardigrades. Four methods of extraction were compared in this study: the light-cooling (L-C) extractor, the high-gradient (H-G), Baermann extractor, the non-gradient (N-G) Baermann extractor and sieves. The results indicate that light and temperature are significant factors influencing tardigrade extraction. The L-C and H-G extractors were more effective than sieves for all substrate categories. These extraction methods (L-C and H-G) therefore seem to be appropriate for quantitative studies of soil and leaf litter tardigrades.

Tardigrades of the Canopy: Evidence of Stratification

Mosses and lichens growing on trees and rocks are a common habitat for limnoterrestrial tardigrades all over the world. However, worldwide tardigrade research has been conducted primarily with ground level samples. In order to determine the presence, absence, diversity, distribution and size of tardigrade populations in the canopy, researchers ascended 135 trees of 17 species at nine northeastern Kansas forest sites, and collected tardigrade habitat from varying heights. Analysis of 822 samples clearly evidenced the presence of tardigrade populations in the forest canopy, as well as documented stratification with a statistically significant increase in density of the tardigrades per sample from 6.4 to 11.9 with increased height. This third dimension discovery must now be factored into theories of tardigrade dispersal. Further investigations may hold new, arboreal species.

The impact of fire on terrestrial tardigrade biodiversity: a first case-study from Portugal

Currently, loss of habitat is the greatest threat to biodiversity, yet little is known about its effect on microscopic animal taxa, such as Tardigrada. One of the causes of habitat destruction is forest fire, both natural and anthropogenic. The latter is commonly used in agriculture to kill insect pests, as a soil preparation, or conservation to create habitat mosaics. In Portugal, 42% of fire frequency is anthropogenic. There is no consensus on the impact of fires on biodiversity, with studies pointing towards different conclusions. Different methods and target taxonomic study groups may partly explain this paradigm. This study is the first into possible effects of habitat destruction on tardigrade populations, in which we analysed the taxonomic and genetic variations of tardigrades from a fire affected location in a Portuguese natural park. Sampling was performed over a 10-year period, from 2000 to 2010. The location was affected by a small fire in 1998 and a big fire in 2003. A total of 11 species from nine separate genera was recorded, from which 19 cox1 haplotypes were identified. Our data suggest a negative effect of a forest fire on tardigrade populations. Taxonomic and genetic richness, as well as abundance show lower levels in the years after a fire, compared with the preceding years. Additionally, the population recovered visibly faster after the small fire than after the bigger one. This is consistent with larger fires destroying larger forest areas, leaving fewer animals at a farther distance available for re-colonisation. Most species found before the main fire are also found after it, indicating these tardigrades have a high recolonisation capability. However, only three of all recorded haplotypes were found both pre and post the main fire, which indicates genetic diversity loss as a direct consequence of fire. Therefore, we conclude that habitat destruction by means of forest fire has a detrimental effect on tardigrade biodiversity, and may have similar effects on other small animals.

Long-term experimental manipulation of moisture conditions and its impact on moss-living tardigrades

The effects of long-term experimentally modified hydration conditions on populations of moss-living tardigrades were investigated in a naturally dry South-Swedish alvar environment at the Island Oland. Carbonite rocks with mosses were collected from rock fences and arranged in three experimental groups: increased dehydration, increased hydration, and control. The total experimental period was 18 months, with treatments applied during two 6 month periods. The density of tardigrade populations was recorded. The total population of tardigrades, all species included, tended to be lower under watering treatment, but the difference was only marginally significant. Populations of Richtersius coronifer and Echiniscus spiniger did not respond to the treatments, while populations of Milnesium tardigradum declined under conditions of increased hydration. The density of eggs in R. coronifer was also lower in the watering treatment. Thus, no positive response to increased hydration was recorded. These results suggest that the tardigrade populations either were not limited by the amount of hydrated periods, or that some other factor(s) counteracted the expected positive response to increased hydration. All populations showed a high variability in density among different moss samples, and the rock from which a sample was taken explained a significant part of this variability. This confirms a commonly believed, but seldom quantified, high heterogeneity in density of semi-terrestrial tardigrades, also among seemingly very similar substrates.

Small-scale Spatial Distribution Variability in Terrestrial Tardigrade Populations

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 dynamics and vertical distribution of enchytraeids and tardigrades in response to deforestation

Abstract In order to increase our present knowledge of the potential impacts of deforestation on the soil ecosystem, we investigated the responses of enchytraeid and tardigrade populations to tree harvesting. The study was conducted in an area of ca. 10 ha located at an altitude of approximately 450 m in the surroundings of the University campus (Vigo, Pontevedra, Spain). Pine forest (Pinus pinaster Aiton), with an average density of 400 trees/ha ranging between 10 and 20 years of age, and some young oaks (Quercus robur L.) were covering the area. At the end of the summer 1995, approximately 50% of the area was harvested. Soil and animal samples were taken from May 1996 to April 1997 at monthly intervals in both forested and deforested areas. Removal of the trees resulted in a significant effect on enchytraeid population numbers and their response was species-dependent in terms of changes in both population numbers and vertical distribution. Higher mortality rates of enchytraeids were recorded in the absence of trees. August seemed to have been critical for survival of all enchytraeid species as no individuals were found in that month and only a few recovered in the following month. Only Cognettia sphagnetorum showed vertical migration in order to avoid adverse conditions. Tardigrades were more abundant in the deforested areas; their ability to enter in a resistant stage could have enabled them to overcome adverse environmental conditions. It is concluded that harvesting of the trees has changed the soil environment and that differences in moisture and temperature conditions are not sufficient to explain the observed differences. The forest soils contained more organic matter than those in the deforested area and therefore differences in the amount and/or quality of the organic matter could be one of the possible explanations for the observed changes in enchytraeid abundance when the forest is removed.

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/m 2. 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.

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.

A new species of Calohypsibius (Phylum Tardigrada, Eutardigrada) from Roan Mountain, Tennessee-North Carolina, U.S.A.

Abstract The ecological distributions of tardigrade species from six sites on Roan Mountain, Tennessee-North Carolina, were determined in a study begun by D.R. Nelson in 1971. Three new species of eutardigrades were discovered in Nelson's study, but remained undescribed. A follow-up to that study was initiated by K.L. McGlothlin in 1988 to determine the long-term stability of tardigrade populations at two of Nelson's original collection sites. Two of Nelson's three new eutardigrade species were rediscovered by McGlothlin, and one newPseudechiniscusspecies was found. The description of one of the eutardigrades,Hypsibius roanensis, was published previously. The remaining eutardigrade found during both studies, a new species ofCalohypsibius, is described here:Calohypsibius schusterisp. nov.

Effects of fungivorous and predatory arthropods on nematodes and tardigrades in microcosms with coniferous forest soil

Effects of fungivorous and predatory soil arthropods on free-living nematodes and tardigrades were studied in a factorial microcosm experiment. A stepwise increase in faunal complexity was obtained by adding soil arthropods to defaunated humus samples from an irrigated+fertilized and an untreated stand of Scots pine. The effects were assessed after 103 and 201 days at 15°C and a soil moisture content of 50% water-holding capacity. The study showed that a diverse community of “fungivorous” arthropods (collembola and oribatid mites), present in numbers similar to those in the field, reduced the abundance of nematodes. A complete community of fungivorous and predatory arthropods (e.g., gamasides, spiders, and cantharid larvae) further strengthened this repressive effect. Certain nematode genera were more affected than others. Tardigrades seemed to be efficient predators on nematodes, but their numbers were, in turn, strongly reduced by predatory arthropods. Because predatory arthropods fed on both nematodes and their tardigrade predators, the impact of arthropod predators on nematode regulation was greater than it appeared to be on the basis of nematode numbers. Humus type also interacted with the other factors. Nematode numbers were initially higher in the untreated humus than in the irrigated+fertilized humus. However, because tardigrade populations increased only in the untreated humus, nematode numbers decreased more in this humus than in the irrigated+fertilized humus. The study demonstrates that nematode abundance can be regulated by a number of types of interacting predators.

The influence of air pollution on moss-dwelling animals: 4. Seasonal and long-term fluctuations of rotifer, nematode and tardigrade populations

The influence of air pollution on moss-dwelling animals: 4. Seasonal and long-term fluctuations of rotifer, nematode and tardigrade populations

A New Species of Hypsibius (Phylum Tardigrada) from Roan Mountain, Tennessee, U.S.A.

A new tardigrade species, Hypsibius roanensis, is described from epiphytic mosses and lichens on beech trees on Roan Mountain, Tennessee. It differs from other species of the genus by the presence of sculptured cuticle with irregular tubercles that increase in size caudally. The buccopharyngeal apparatus consists of narrow buccal tube, well-developed apophyses, and spherical pharynx with two granular macroplacoids. Roan Mountain is the highest cross range between the Unaka Mountains and the Blue Ridge Mountains in the Southern Appalachians. The north-facing slope of the mountain is in Carter County, Tennessee; the south-facing slope is in Mitchell County, North Carolina. Tardigrades were first recorded from Roan Mountain by Riggin (1962), who found three species of Macrobiotus at 1,890 m in Tennessee. Maucci (1987) reported 10 species in five genera (Macrobiotus, Diphascon, Minibiotus, Itaquascon, and Milnesium) from mosses collected in the spruce-fir forest of Roan Mountain above 1,829 m. The most extensive study of tardigrades on Roan Mountain was by Nelson (1973, 1975), who examined the ecological distribution of 21 species from epiphytic mosses on beech trees at approximately 1,219 m, 1,524 m, and 1,654 m on both the northand southfacing slopes. Nelson found nine specimens of new species of Hypsibius (designated Hypsibius a in Nelson, 1975). However, multiple specimens from sample were mounted per slide in non-permanent medium (Turtox CMC9), and the slides were unsuitable for identification after 10 years. McGlothlin (1990) collected again at two of Nelson's sites to determine the long-term stability of tardigrade populations and rediscovered the new species of Hypsibius. The new species is described here. MATERIALS AND METHODS On 8 September 1988, epiphytes (primarily mosses) were collected from beech trees at approximately 1,524 m and 1,654 m on the north-facing slope of Roan Mountain, Carter County, Tennessee (Nelson's stations 5N and 6N). Fifty-six samples were collected, 27 from the 5N station and 29 from 6N. Each sample was placed in stoppered funnel and soaked in tap water for 24 h to allow the animals to become active and then go into anoxybiosis. The epiphyte was removed and squeezed over the funnel to recover the maximal number of tardigrades. The contents of the funnel were drained into beaker, and the top layer of water was decanted. Boiling water was added to the beaker to kill the tardigrades. Then the contents of the beaker were rinsed through two sieves, TRANS. AM. MICROSC. SOC., 112(2): 140-144. 1993. ? Copyright, 1993, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.127 on Tue, 28 Jun 2016 06:58:43 UTC All use subject to http://about.jstor.org/terms VOL. 112, NO. 2, APRIL 1993 no. 18 mesh (1 mm) and no. 325 mesh (0.045 mm), simultaneously. The material remaining on the no. 325 sieve was washed into jar with 95% ethanol. Later, the contents of the jars were examined in gridded Petri dish under darkfield stereomicroscope at 25 x. Tardigrades were transferred with an Irwin loop to small vials containing 95% ethanol. Up to 35 tardigrades were mounted per sample. Each specimen was removed with an Irwin loop and placed in Hoyer's mounting medium on microscope slide and sealed with coverslip. After the medium had dried completely, the coverslip was ringed with epoxy paint. Identifications were made using an interference phase-contrast compound microscope with oil immersion. Measurements were made with calibrated ocular micrometer. Drawings were made with drawing tube and photographs were taken with Kodak T Max? 100 film. The scanning electron micrograph is from Nelson's (1973) original study of Roan Mountain tardigrades.

Dispersal ofRamazzottiusand other tardigrades in relation to type of reproduction

Summary The relationships between the type of reproduction and sexuality and the types of substrates inhabited by semiterrestrial tardigrade populations are reported. Specimens of the genus Ramazzottius (Eutardigrada, Hypsibiidae) were collected from a limited area of hilly to mountainous zones near Modena and Reggio Emilia (Italy). The lichen substrate Xanthoria parietina, typically colonized by R. oberhaeuseri, was the main subject of study, though animals were also extracted from moss cushions. The sex ratio, correlated with the type of reproduction, clearly differed when the lichen or moss samples were collected from tree trunks or limited rocky areas, or came from extensive rocky outcrops. In the former case, the cytological characteristics of oocytes and the absence of males attest to thelytokous parthenogenesis. In the latter, some male specimens were always found, though several samples showed cytological evidence of parthenogenetic and amphimictic females. Differences in the distribution and freq...

Response of soil nematodes, rotifers and tardigrades to three levels of season-long sulfur dioxide exposures

Soil nematode, rotifer, and tardigrade populations were sampled in field plots of native northern mixed prairie in southeastern Montana from 1977 to 1979. The field plots were exposed to season-long fumigation with controlled low-levels of SO2 throughout the growing seasons (April–October). Two field sites were used, one fumigated for five seasons (1975–1979) and the other for four (1976–1979). Seasonal average SO2 concentrations ranged from control (< 1 pphm) to approximately 7 pphm. Soil fauna were sampled by taking soil cores and extracting them by the Baermann wet funnel technique. Total counts were made for tardigrades and rotifers while nematodes were divided into three groups-stylet bearers (Tylenchida-Dorylimida), non-stylet bearers, and the predatory Mononchida. Consistent trends of substantial reductions in tardigrade populations occurred in all treated plots in all years; however, statistical significance was achieved only in 1979 when sample size and individual core size were substantially increased. Tardigrades were found to be restricted almost completely to the surface two centimeters of the soil profile. Significant population reductions in the treated plots of both sites were found for non-stylet bearing nematodes in 1977 only. Stylet bearing types and predaceus Mononchida appeared unaffected by the SO2 as were the soil rotifers, although slight but consistent trends of reduction in rotifers occurred in the highest treatments in 1977 and 1978. Both nematodes and rotifers were distributed primarily in the 0 to 10 cm layer of the soil profile but not restricted to the soil surface as much as the tardigrades. Implications of the responses to SO2 and vertical distributions of the three groups are discussed.

Effect of four insecticides on the pasture ecosystem

Fensulfothion, fenitrothion, carbofuran, and DDT were applied as granules to the surface of a pasture at insecticidal rates (2.24 kg a.i./ha). Fensulfothion significantly (P < 0.01) depressed nematode numbers for at least 30 weeks and carbofuran only at 20 weeks after treatment. Tht effect was greatest in the surface layer (0-30 mm) of soil. Most groups of nematodes showed no treatment effect, but the Tylenchida, in particular Tylenchus spp. other than T. emarginatus, and the Mononchidae were depressed by fensulfothion and Paratylenchus by carbofuran. There were some significant differences between treatments in rotifer and tardigrade populations and on one occasion tardigrade numbers were greater in the DDT treated plots than the control (P < 0.05).

Food from a Northern Environment

A sister group of the Arthropoda, the Tardigrada are micrometazoans that occupy a diversity of niches in freshwater, marine, and terrestrial habitats. Commonly called water bears because of their slow, lumbering gait, these molting lobopods have four pairs of legs, usually terminating in claws. Most are less than 1 mm in length, with a complete digestive tract, a dorsal gonad with one or two gonoducts, and a dorsal lobed brain with a ventral nerve cord and four bilobed ganglia, one per leg-bearing metamere. The body cavity (hemocoel) functions in respiration and circulation. Over 1200 species have been described based primarily on the morphology of the claws and buccal-pharyngeal apparatus. Individuals may be either gonochoric, unisexual, or hermaphroditic, with fertilized or unfertilized eggs deposited either freely or within the shed exuvium. Parthenogenesis occurs frequently in limnic and terrestrial tardigrades, allowing them to colonize new territories by passive dispersal of a single individual. Cryptobiosis (anhydrobiosis, anoxybiosis, cryobiosis, and osmobiosis) and diapause (encystment and resting eggs) occur during the life history. Active adults (surrounded by water) and cryptobiotic adults and eggs are primarily dispersed passively, but some active dispersal can also occur. Due to the characteristic patchy distributions of tardigrade populations, little is known about their population dynamics and trophic relationships. Improved methods for collection, microscopy, culturing, and molecular analyses have been have contributed much to our knowledge of tardigrades.