Limnic Species Research Articles

Factors contributing to the potential expansion of Limnomonas gaiensis (Chlamydomonadales, Chlorophyta) in freshwater lakes in Northern Europe

ABSTRACTLimnomonas gaiensis is a recently described green microalga inhabiting freshwater lakes in northern Europe (England, Sweden). There is little information on the species’ tolerance to environmental factors and its capacity to spread to unconnected lakes. Using a barcoding approach, we investigated the phylogeography of L. gaiensis along a latitudinal gradient spanning 54–60°N. Experimental long-term exposure to a gradient of water temperatures, mimicking natural conditions, was performed to assess its thermal tolerance. Genetic analyses showed that this limnic species is easily identified at the species level. Phylogeographic analyses revealed the existence of two genetically similar haplotypes over the mitochondrial cytochrome C oxidase subunit 1 gene in different countries, suggesting that the range of L. gaiensis has recently expanded from a common source lineage, despite geographic isolation. Heterogeneity in the Helix III of the nuclear Internal Transcribed Spacer 2 region of the English strain suggested past hybridization. Physiological analyses showed that L. gaiensis can survive and reproduce asexually, potentially year-round. Optimal growth was observed at 15°C, with a doubling time of 1.1 days. The species is able to survive short periods of desiccation. The lack of connectivity between the lakes where the species was sampled rules out aquatic dispersal of this species. However, its physiological features make L. gaiensis a good candidate for propagule dispersal by either wind or human/animal-mediated transportation. Our study calls for further investigation into limnic systems, using rapid barcoding, with concurrent atmospheric and physiological analyses to establish its distribution over wider geographic scales and to understand how L. gaiensis disperses.

Sharp claws beneath our feet – the diversity of tarsal attachment devices of oribatid mites (Acari, Chelicerata, excluding Astigmata) – a review

ABSTRACT The majority of animals possess claws on their legs and they are mainly used for keeping attached to the substrate. Recent studies on claw shapes and function suggest that claws are not just simple attachment devices but highly specialized morphological traits bearing information about lifestyle, ecology and evolution. In that respect, knowledge about claws is extremely scarce, especially in highly diverse groups, as for example the oribatid mites, with more than 11000 named species occurring in every environment all over the world. This review summarizes all information about claws and relevant aspects for this large group of arthropods. There is a huge variety of ambulacral claw morphologies present in oribatid mites and this diversity does not follow a strict phylogenetic or systematic pattern. Lifestyle and ecology apparently play an important role in shaping claw morphologies. Intertidal oribatid mites are mostly characterized by having single large tarsal claws to withstand tidal flooding, a similar tendency can be found in terrestrial limnic species where monodactylous species prevail. Additionally, fresh-water Oribatida often show scaliform and barbed distal tarsal setae which cooperate with the claws helping the mites to stick to water plants. Claws of arboreal mites are often equipped with adhesive pads “pulvilli” allowing them to walk on smooth plant surfaces. Suction pads are also found in a few mites showing epilithic lifestyles and in mites being able to perform sudden evasive jumps. Claws of phoretic oribatid mites show in most cases no apparent adaptations but certain groups are equipped with highly modified claws allowing them to attach to specific structures of their hosts. Finally, this review gives an overview of all claw morphologies present in each larger phylogenetic oribatid mite group.

Ostracod Response to a Major Middle Jurassic Sea-Level Fall: A Case Study from Southern Tunisia (North Gondwana) with Implications on Regional Stratigraphy and Palaeoenvironmental Reconstruction

Marginal-marine to non-marine ostracod assemblages from the Bajocian (Mid-Jurassic) of southern Tunisia, precisely from the Krachoua Formation at the Kef El Anneba section near the Beni Kheddache area, are here described and tested for their utility to improve the stratigraphic accuracy and palaeoenvironmental reconstructions. This particular microfauna consists of 11 species belonging to 6 genera and represents 2 distinct types of species-rich assemblages from this time interval, allowing the interpretation of the depositional setting of the fossiliferous horizon from which the samples derive. The first ostracod assemblage is mainly composed of the brackish to shallow marine species Fastigatocythere sp. Mette, 1995; Vernoniella aff. V. bajociana Bate, 1965b; Paracypris sp. A, Paracypris sp. B, Fabanella sarda Malz et al., 1985; Marslatourella aff. M. bathonica Andreu, 1999; and Fabanella aff. F. bathonica Oertli, 1957. This ostracod biofacies reflects marginal marine (shallow platform, restricted lagoon) conditions in the studied area. In contrast, the second ostracod assemblage is exclusively dominated by the non-marine limnic species Alicenula sp., Theriosynoecum pusilla Rohr, 1976; Theriosynoecum aff. T. aveyronensis Rohr, 1976; and Theriosynoecum sp. Such ostracod biofacies reflects the establishment of (a) permanent freshwater lake(s) in the studied area, triggered by the total emersion of the Bajocian Krachoua platform, presumably as response to the short-term sea-level fall event JBj3 of Haq (2017). The recognized ostracod species from the upper part of the Krachoua Formation at Kef El Anneba section (Medenine area) are particularly similar to those already described from the neighbouring sections of Kezzani (Dhaher area) and Krachoua (Tataouine area), facilitating a stratigraphic calibration of the Krachoua Formation, as well as regional correlations of the respective Bajocian continental event within the southern Tunisian palaeogeographic domain. Moreover, the biogeography of the studied ostracod microfauna from the Mid-Jurassic of southern Tunisia provides further arguments to support the hypothesis of significant biological exchanges between Laurasian and Gondwanan islands, as recently demonstrated by means of a charophyte microflora, indicating that Peri-Tethyan biogeography remained relatively uniform during that time interval and challenging the previous assumption of their endemism.

Food-web comparisons between two shallow vegetated habitat types in the Baltic Sea

Coastal vegetated habitats maintain highly diverse communities, where the contribution of macrophyte production is significant for macroinvertebrate primary consumers. In the brackish-waters of the Baltic Sea, the taxonomical diversity of different macrophytes includes both marine and limnic species. To study the basal food-web differences of two key vegetated habitat types, either dominated by a perennial brown macroalgae (Fucus vesiculosus) or by angiosperm plants, 13C and 15N compositions of different primary producers and macroinvertebrate consumers were examined, and their diets were estimated by Bayesian mixing models. Carbon isotope diversity of primary producers was high especially in the hard-bottom Fucus-dominated habitats, which was also reflected in a larger consumer isotope niche. However, consumer isotope niche among sites was similar within the same habitat type. Our models indicated that the perennial macrophyte dietary median contribution was about 25% for deposit feeders and omnivores in both habitat types, while epigrazers preferred filamentous algae (30–60%). The niche positions of the abundant clams L. balthica, M. arenaria and C. glaucum differed between the two habitats, but they showed only small (<10% units) differences in their macrophyte dietary contributions. The isotopic compositions of the dominating primary producer assemblage reflected significantly in the isotope niche structure of the associated primary consumers.

Comparison of the transcriptomes of two tardigrades with different hatching coordination

BackgroundTardigrades are microscopic organisms, famous for their tolerance against extreme environments. The establishment of rearing systems of multiple species has allowed for comparison of tardigrade physiology, in particular in embryogenesis. Interestingly, in-lab cultures of limnic species showed smaller variation in hatching timing than terrestrial species, suggesting a hatching regulation mechanism acquired by adaptation to their habitat.ResultsTo this end, we screened for coordinated gene expression during the development of two species of tardigrades, Hypsibius exemplaris and Ramazzottius varieornatus, and observed induction of the arthropod molting pathway. Exposure of ecdysteroids and juvenile hormone analog affected egg hatching but not embryonic development in only the limnic H. exemplaris.ConclusionThese observations suggest a hatching regulation mechanism by the molting pathway in H. exemplaris.

Dominance of competitors in riparian plant species composition along constructed banks of the German rivers Main and Danube

Hardening of shorelines has been extensively implemented in many parts of the developed world. This also applies to banks of German Federal Waterways, which are mostly fixed by ripraps to prevent bank erosion as a consequence of wave disturbance by shipping traffic. Since ripraps notably alter functions of riparian ecosystems and nature conservation demands recently gained in importance along waterways, alternatives for ripraps play an increasing role.Front-fixed banks are ripraps parallel to the shoreline and embedded in the waterway’s channel with an unsecured bank of low steepness behind them. Thus, they are suitable to prevent banks from erosion. However, it is unclear how they can contribute to the ecological enhancement of riparian vegetation along waterways.Therefore, we compared riparian vegetation of ripraps and front-fixed banks with unsecured banks along the German rivers Main and Danube to assess the ecological efficiency of front-fixed banks. Disturbance by alternating water levels was the lowest at ripraps, whereas disturbance levels were higher at front-fixed and unfortified banks. We used an ordination and indicator species analysis to reveal differences in species composition. The results of the indicator species analysis were analyzed regarding species’ biotope origin, light and moisture demand and life strategy. We analyzed species diversity and calculated functional diversity indices to display the prevalent ecosystem processes.Higher variation in species composition, common indicator species, a strong vertical layering of woody riparian vegetation and similar site conditions at front-fixed and unfortified banks revealed higher similarities in species composition between them than to other bank type combinations. Limnic species occurred with a higher frequency at unfortified and front-fixed banks, whereas terrestrial species were more frequent at ripraps. Light-tolerant species were more common at ripraps, whereas species’ demand for moisture was higher at front-fixed and unfortified banks than at ripraps. Cr-strategists occurred more frequently with increasing disturbance level, whereas c-strategists were more common at ripraps.Ripraps had the highest species diversity levels whereas functional diversity tended to be higher at front-fixed and unfortified banks. This indicates a higher trait complementarity and thus a higher specialization towards alternating water levels, wherefore a higher degree of naturalness can be assumed in these habitats.Nature conservation efforts along German Federal Waterways should focus on the restoration of flooding dynamics, as species typical for riverine habitats are more common at front-fixed and unfortified banks than at ripraps. Since front-fixed banks bear traits suited for the reconnection of rivers and their floodplains and for bank protection, they are a suitable alternative to promote biodiversity along German Federal Waterways.

THE MOLLUSCA COLLECTION OF THE MUSEU NACIONAL / UFRJ – HISTORICAL SYNTHESIS

A Coleção de Mollusca do Museu Nacional/UFRJ é a mais antigs antiga e uma das maiores no Brasil. Atualmente, ela inclui 39.631 lotes registrados de todas as classes do filo, exceto Monoplacophora, além de muitos outros em processo de tombamento. A maioria dos lotes provêm de localidades no Brasil, mas espécies de localidades no exterior também estão representadas. Espécies marinhas são as mais representativas, mas espécies de ambientes terrestre e límnico também estão depositadas, assim como material de sítios de Sambaqui. A coleção abriga 671 lotes de tipos, de 347 nomes, sendo 132 holótipos e um neótipo. A coleção teve seu início no final do século XIX e cresceu em diferentes taxasao longo de sua história, como resultado de coletas intensivas no Brasil, e também pela doação de coleções particularesa e uma das maiores no Brasil. Atualmente, ela inclui 39.631 lotes registrados de todas as classes do filo, exceto Monoplacophora, além de muitos outros em processo de tombamento. A maioria dos lotes provêm de localidades no Brasil, mas espécies de localidades no exterior também estão representadas. Espécies marinhas são as mais representativas, mas espécies de ambientes terrestre e límnico também estão depositadas, assim como material de sítios de Sambaqui. A coleção abriga 671 lotes de tipos, de 347 nomes, sendo 132 holótipos e um neótipo. A coleção teve seu início no final do século XIX e cresceu em diferentes taxasao longo de sua história, como resultado de coletas intensivas no Brasil, e também pela doação de coleções particulares

Identification of the trehalose-6-phosphate synthase (tps) gene in desiccation tolerant and intolerant tardigrades

The non-reducing disaccharide trehalose is one of the molecules involved in anhydrobiosis, acting as bioprotectant of cells exposed to desiccation. The main biosynthesis pathway of trehalose involves a glycosyl-transferase, trehalose-6-phosphate synthase (TPS), encoded by a gene (tps) whose presence and characterization has been studied in different metazoans. The tps gene is here identified for the first time in Tardigrada in twelve species belonging to both Heterotardigrada and Eutardigrada. The tps gene is found in all semiterrestrial and anhydrobiotic species examined, correlating trehalose presence with anhydrobiotic ability. In contrast, tps is not detected in two limnic and desiccation intolerant species. The surprising presence of tps in another limnic and desiccation intolerant species, Dactylobiotus parthenogeneticus, allows us to infer that in tardigrades trehalose could be produced and involved, not just in anhydrobiosis, but also in the regulation of other biological functions, such as encystment. The analysis of nucleotide tps sequences shows a very high conservation of the gene inside the phylum Tardigrada, while amino acid sequences further support the relationship between Tardigrada and Pancrustacea.

North American freshwater Halacaridae (Acari): literature survey and new records

ABSTRACT Ten species from eight freshwater halacarid genera and three limnic species from three marine genera are at present recorded from North America. The species are illustrated, their morphological characters, ecological data and distribution in North America outlined. The North American fauna of freshwater halacarids is similar to that of Europe, both in respect to presence and abundance of species. In contrast, the freshwater inhabiting species of otherwise marine genera in North America are not found outside this continent.

A new limnic species of Macrostomum (Platyhelminthes: Macrostomida) from Argentina and its muscle arrangement labeled with phalloidin

A new species of Macrostomum from limnic environments in Argentina is described. Macrostomum platensis n. sp. differs from its congeners by the shape and length of its stylet. Moreover, the arrangement of the muscle system is described using rhodamine-labeled phalloidin. This method provides detailed information on the complex arrangement of muscles of the body wall, pharynx, head and reproductive organs. The resulting description is compared with previously published ones using the same methodological approach. The muscle arrangement may be considered for future taxonomic studies within the genus Macrostomum and might provide phylogenetically useful characters.

Survival of freezing by hydrated tardigrades inhabiting terrestrial and freshwater habitats

The seasonality and unpredictability of environmental conditions at high altitudes and latitudes govern the life cycle patterns of organisms, giving rise to stresses that cause death or development of specific adaptations. Ice formation is a major variable affecting the survival of both freshwater fauna and fauna inhabiting lichens, mosses and leaf litter. Tardigrades occupy a wide range of niches in marine, freshwater and terrestrial environments. The highest number of species is found in terrestrial habitats thanks to their ability to enter anhydrobiosis and cryobiosis. The cryobiotic ability of tardigrade species from polar regions is well known. Consequently, we focused our research on the ability to survive freezing in the active hydrated state using seven tardigrade species differing in phylogenetic position and collected at various altitudes and from different habitats in a temperate area. Specimens were cooled at different cooling rates (from 0.31 °C min −1 to 3.26 °C min −1). Even though the final survival and the time required by animals to recover to active life were both inversely related to the cooling rate, highly significant interspecific differences were found. Species survival ability ranged from excellent to none. Species living in xeric habitats withstood freezing better than those living in hygrophilous habitats, while true limnic species did not exhibit any cryobiotic ability. The ability to withstand freezing seems linked to the anhydrobiotic ability. The differences in cryptobiotic performance among tardigrade species seem more influenced by selective pressures linked to local adaptation to habitat characteristics than by phylogenetic relationships.

Ultrastructural observations of the protonephridia of Polymerurus nodicaudus (Gastrotricha: Paucitubulatina)

AbstractKieneke, A. and Hochberg, R. 2012. Ultrastructural observations of the protonephridia of Polymerurus nodicaudus (Gastrotricha: Paucitubulatina). —Acta Zoologica (Stockholm) 93: 115–124.We studied different regions of the protonephridia of the limnic gastrotrich Polymerurus nodicaudus by means of light and electron microscopy to determine how freshwater species might differ from their marine relatives. Microscopic and ultrastructural characters are in accordance with another limnic species of Paucitubulatina, Chaetonotus maximus, whose protonephridial system has been previously reconstructed. Shared protonephridial characters of both species include the presence of highly elongate terminal organ cilia, microvilli, and the canal cell lumen as well as the presence of a conspicuous anterior loop of the protonephridial lumen. These features are not present in representatives of earlier, marine, paucitubulatan lineages (i.e., Xenotrichulidae) and so are assessed as evolutionary novelties that were likely important for the successful colonization of the freshwater environment.

Riesgo de establecimiento del gasterópodo dulceacuícola invasor Melanoides tuberculatus (Thiaridae) en el Río de la Plata (Argentina-Uruguay)

Melanoides tuberculatus is a cosmopolitan gastropod that has invaded and has now spread into most countries of the American continent. Introduction pathways remain unknown in most cases. This work draws attention on the colonization risks of this species in the Rio de la Plata area as a consequence of its record in flower and pet shops – in the city of La Plata (Buenos Aires, Argentina) - in which limnic species are sold. The species was identified at the beginning of 2009 within a lot of 29 specimens from a shop, and this is the southernmost record of this species in the Plata Basin. Subsequent surveys in 3 commercial shops in the same city revealed its presence in 2 of them. This was related to the purchase of ornamental plants by the shops. Identification of this species in the city of La Plata should be carefully assessed, because of the potential consequences that settlement of this mollusk in the Rio de la Plata may have on displacement of the local fauna and on public health.

Stress response of a boreo-alpine species of tardigrade, Borealibius zetlandicus (Eutardigrada, Hypsibiidae)

Invertebrates living in extreme environments as well as those living under unpredictable habitat conditions must be able to survive severe environmental stresses bound to their habitats. Tardigrades represent a good animal model to analyze responses evolved by organisms to overcome extreme environmental stresses or to colonize extreme environments because they respond to desiccation or freezing in their habitats by entering cryptobiosis. The responses to environmental stresses have been evaluated almost exclusively in terrestrial tardigrades, while very little is known about the ability of limnic species to tolerate those stresses. This study evaluates the responses of the limnic boreo-alpine species Borealibius zetlandicus, under lab conditions, to stresses imposed by desiccation and temperature variation (freezing and heating). Our results indicate that active specimens are able to freeze, confirming the cryobiotic ability of this species. There is a negative correlation between survival and cooling rates. In contrast, no specimens of B. zetlandicus are able to survive desiccation. With regard to thermal tolerance, the animals show a high ability to resist heat-shock (LT50 = 33.0 ± 0.5 °C) for a short time. This wide tolerance to different environmental parameters could be the reason for the wide distribution of the species. Due to the disjunct distribution of the species and to the potential presence of cryptic tardigrade species that could have different ecological and physiological responses, we decided to characterize the population studied from a molecular point of view by investigating its COI mtDNA sequences.

Distribution et écologie des associations d’ostracodes récents de l’estuaire de Tahadart (Maroc Nord-Occidental)

Forty-five ostracod species were identified for the first time in the Tahadart estuary (NW Morocco). They can be grouped into five different ecological assemblages, which characterise four estuarine ecozones. A first ecozone occurs in temporary waters located between the tidal channels of the inner estuary and it is characterised by ostracod species typical of fresh to brackish waters. In the main estuary area, the ostracod fauna is dominated by clearly euryhaline species that account for nearly 70% of the entire fauna. The relative abundance of the different assemblages allows us to subdivide the estuarine environment along a longitudinal profile into mouth, outer and inner estuary. The estuary's mouth displays the highest values of marine euhaline, phytal and periphytal as well as ubiquitous species and the lowest values of very euryhaline species; the latter are the only species present in the inner estuary. The outer estuary exhibits intermediate percentages of the different ecological assemblages. This distribution, characterized by the absence of limnic species, points to the influence of marine waters in an open estuary with a low fresh water input. In the estuary's mouth, as well as in the outer estuary, where the slikke and schorre are well developed, the distance to the emersion line is underlined by the lower occurrence of marine and ubiquitous species and the higher occurrence of the very euryhaline ones. The Tahadart estuary displays a moderate to high ostracod diversity with distinct differences among the ecological zones. The stress of this environment is highlighted by the low diversity characteristics of extreme environments, alike in the inner estuary and in some areas located far from the emersion level. The relative position with respect to the emersion line, as well as the presence of gross detritic sediments and vegetation, appear to be of importance for the good development of the ostracods.

Reconstruction of an Aquatic Food Web: Viking Haithabu vs. Medieval Schleswig

In the last two decades, the analysis of stable isotopes of carbonate and collagen from archaeological bone finds became a useful tool in the reconstruction of ancient food webs. Nevertheless there is still only little information available about aquatic food webs, in particular concerning brackish water ecosystems. The Schlei Fjord in Schleswig-Holstein, Germany, is such an ecosystem and was investigated to determine stable isotopic values for nitrogen, carbon and oxygen from bone collagen and carbonate in archaeological bone finds. Wild birds, mammals and fish bones from the Viking settlement Haithabu and the medieval town of Schleswig have been analyzed in this study to determine stable isotope values for marine and limnic species and to investigate possible isotopic gradients for mixing fresh water and salt water ecosystems.

Encystment Processes and the “Matrioshka-like Stage” in a Moss-dwelling and in a Limnic Species of Eutardigrades (Tardigrada)

Tardigrades have two forms of dormancy, namely cryptobiosis and encystment. The encystment is a form of diapause known for a limited number of species of tardigrades and still little studied. To increase the knowledge on encystment, two species of eutardigrades from Italy have been considered: the moss-dwelling Amphibolus volubilis (Eohypsibiidae), and the limnic Dactylobiotus parthenogeneticus (Murrayidae). Cysts have been collected in nature, or induced under laboratory conditions. In the latter case, it was possible to follow the several steps of encystment processes. Two different types of cyst (“type 1” and “type 2”) have been found in A. volubilis, while in D. parthenogeneticus only one type has been found. In general, the ovoid-shaped cysts are constituted by a series of cuticles surrounding the animals and resemble an onion or a Matrioshka Russian doll. In all three types of cyst, the encystment processes show both common and peculiar traits. Encystment begins with the discharging of the sclerified parts of the buccal-pharyngeal apparatus, as in the molting process, but without the loss of the old cuticle. Then, two or three new cuticles are serially synthesized, according to cyst type. In A. volubilis, the ultrastructure of these new cuticular involucra is similar to that of non-encysted animal cuticles, while in D. parthenogeneticus the ultrastructure of the new cuticular involucra differs from that of non-encysted animal cuticle. A modified buccal-pharyngeal apparatus has been observed both in “type 2” cyst of A. volubilis and in the D. parthenogeneticus cyst.

Zoobenthic diversity-gradients in the Baltic Sea: Continuous post-glacial succession in a stressed ecosystem

The Baltic Sea, formed after the latest glaciation, is an enclosed, low-saline, non-tidal ecosystem and has steep latitudinal and vertical gradients from sub-arctic conditions in the north to temperate in the south. The sea has undergone rapid changes since the glaciation, and the “ecological age” of the present ecosystem is only about 8000 years. Primary successional processes are still ongoing, and numerous ecological niches (e.g. large-bodied sediment bioturbators) remain available for immigration. The system is species-poor and vulnerable to the threat of exotic invasive species, and to date about 50 zoobenthic species have established populations in the Baltic Sea. The present biota is a mixture of species of different ecological and zoogeographical origin (marine to limnic; northern Arctic marine and limnic, to North Sea and Atlantic marine). The current distribution patterns of zoobenthos are illustrated, using marine, limnic and non-indigenous examples of structure and ecosystem functions. The species richness decreases from over 1600 marine benthic species in the open Skagerrak to about 500 in the western parts of the Baltic Sea, approximately 80 in the southern regions, to less than 20 in the northern regions. On the other hand, limnic species increase diversity in the inner reaches of the Gulf of Finland and the Gulf of Bothnia. Polychaetes, molluscs and echinoderms are dramatically reduced in numbers from the south to the north.

The Evolution of Advanced Mechanical Defenses and Potential Technological Applications of Diatom Shells

Diatoms are unicellular algae with silicified cell walls, which exhibit a high degree of symmetry and complexity. Their diversity is extraordinarily high; estimates suggest that about 10(5) marine and limnic species may exist. Recently, it was shown that diatom frustules are mechanically resilient, statically sophisticated structures made of a tough glass-like composite. Consequently, to break the frustules, predators have to generate large forces and invest large amounts of energy. In addition, they need feeding tools (e.g., mandibles or gastric mills) which are hard, tough, and resilient enough to resist high stress and wear, which are bound to occur when they feed on biomineralized objects such as diatoms or other biomineralized protists. Indeed, many copepods feeding on diatoms possess, in analogy to the enamelcoated teeth of mammals, amazingly complex, silica-laced mandibles. The highly developed adaptations both to protect and to break diatoms indicate that selection pressure is high to optimize material properties and the geometry of the shells to achieve mechanical strength of the overall structure. This paper discusses the mechanical challenges which force the development of mechanical defenses, and the structural components of the diatom frustules which indicate that evolutionary optimization has led to mechanically sophisticated structures. Understanding the diatom frustule from the nanometer scale up to the whole shell will provide new insights to advanced combinations of nanostructured composite ceramic materials and lightweight architecture for technological applications.

Experiences with dormancy in tardigrades

Tardigrades often colonise extreme habitats, in which they survive using both types of dormancy: quiescence and diapause. Together with nematodes and bdelloid rotifers, tardigrades are known to enter quiescence (with several forms of cryptobiosis: anhydrobiosis, cryobiosis, anoxybiosis, osmobiosis) at any stage of their life cycle, from egg to adult. Entering anhydrobiosis, tardigrades contract their body into a so-called tun, loosing most of their free and bound water (&gt;95%), synthesizing cell protectants (e.g., trehalose, glycerol, heat shock proteins) and strongly reducing or suspending their metabolism. Our research on cryptobiosis focused on some ecological and evolutionary aspects. We evaluated: i) the long-term anhydrobiotic survival by comparing quantitative data on recovery from naturally induced desiccation in several species of tardigrades; ii) differences in survival patterns between species and populations by experimentally inducing anhydrobiosis and cryobiosis; iii) phenotypic factors affecting anhydrobiotic survival. As regards diapause, we considered encystment and eggs. Encystment involves at least the synthesis of new cuticular structures. Morphological changes during cyst formation are more complex than those involved in tun formation. We analyzed more in detail encystment processes, comparing a semiterrestrial with a limnic species. Several inter-specific differences have been identified, other than the production of two types of cysts in the semiterrestrial species. Our analysis of life history traits of a laboratory reared strain of a soil tardigrade revealed a particular hatching phenology that involved the production of both subitaneous and resting eggs. The latter need a cue to hatch (dehydration followed by re-hydration). In addition, the evolutionary meaning of dormancy in tardigrades is discussed.