1,721,179 research outputs found
Ultrastructural study of spermiogenesis and the testicular and spermathecal spermatozoon of the gonochoristic tardigrade Xerobiotus pseudohufelandi (Eutardigrada, Macrobiotidae)
No full textThis paper investigates by scanning and transmission electron microscopy spermiogenesis and spermatozoon morphology of the gonochoristic eutardigrade Xerobiotus pseudohufelandi (Macrobiotidae). During spermiogenesis clusters of spermatids are connected by cytoplasmic bridges that persist up to an advanced stage of maturation. Spermiogenesis is characterized by distinctive modifications of the nucleus and by the differentiation of an acrosome, tail and substantial midpiece. Testicular spermatozoa are folded with the hinge located between the head and midpiece, thus resembling a nut-cracker. The head includes a rod-shaped, bilayered acrosome and an elongated, helicoidal nucleus with condensed chromatin. The large kidney-shaped midpiece has hemispherical swellings/ovoid elements surrounding the centriole and an incomplete mitochondrial sleeve. The flagellum contains a ́9 + 2 ́ axoneme and terminates in a tuft of microtubules. Spermathecal spermatozoa always have linear profiles. The acrosome and nucleus have the same morphological pattern as in testicular spermatozoa, whereas the midpiece is thin and lacks the hemispherical swellings, and the tail is reduced to a short stub. Functional considerations are presented, based upon this different morphology. Moreover, phyletic comparisons are made on the basis of sperm morphology, both for the family Macrobiotidae and the class Eutardigrada
Karyological analysis on Macrobiotus pseudohufelandi (Tardigrada, Macrobiotidae) and a new finding of a tetraploid population
No full textThree populations of Macrobiotus pseudohufelandi (Eutardigrada, Macrobiotidae) were studied with karyological techniques not previously utilized for tardigrades. These observations provided detailed information on the karyology of these animals, particularly single chromosome morphology. A diploid amphimictic cytotype and a triploid thelytokous parthenogenetic cytotype were confirmed. In addition, a new tetraploid thelytokous parthenogenetic cytotype was found. Tetraploidy, as defined by chromosome number, was confirmed by DNA-Feulgen content evaluations. Indeed, the minimum DNA content in the tetraploid population is about four fold that in sperm from the diploid population
The spermatozoon in tardigrades: Evolution and relationships with the environment
No full textThe spermatozoon ultrastructure of seven species of tardigrades, one heterotardigrade echiniscid and six eutardigrades, was analysed and described. Tardigrade species were collected from freshwater sediments, moss and leaf litter. A phylogenetic evaluation was made and relationships of spermatozoon shape and habitat were discussed. The spermatozoon morphology of the moss-dwelling echiniscid (heterotardigrade) was very similar to that found in marine species of the same order. This indicates that in Echiniscoididae change of habitat had little influence on sperm structural organisation. In contrast, eutardigrade spermatozoa. have developed several different structural organisations that may be related to family and/or habitat
Dry and survive: the role of antioxidant metabolism in anhydrobiotic organisms.
No full textAlthough evolution of life has turned oxygen into a vital compound for most organisms, this element can also have deleterious effects on living systems. Oxidative stress is a process resulting from an imbalance between excessive production of reactive oxygen species (ROS) and limited action of antioxidant defenses. It is a particularly harmful health risk factor, common to the development of several chronic human pathologies (e.g. cancer, Alzheimer’s and Parkinson’s) and believed to play a major role in the ageing process. Thus antioxidant protection is essential for survival under an aerobic environment.
Water too is essential for life, but some organisms have the ability to survive extreme desiccation by entering into a state of suspended animation called anhydrobiosis. These organisms are widespread throughout nature, including bacteria, protists, yeasts, plants and animals. The loss of water involves important biological processes such as changes in metabolism, alterations of cell membranes, and production of oxidative stress. Therefore, the maintenance of life in the absence of water requires a complex set of mechanisms working in close coordination, such as the accumulation of bioprotectant molecules, the activation of molecular repair mechanisms and of antioxidant and molecular chaperone systems.
Oxidative stress seems to be one of the most deleterious effects of water depletion, since the susceptibility to oxidative damage may increase with dehydration. Anhydrobiotes seem to apply two main strategies to cope with the danger of oxygen toxicity, namely an increasing efficiency of antioxidant defences and a metabolic control of both energy-production and energy-consuming processes. Tardigrades are here presented as model system to evaluate the effective damages induced by an increase of ROS production during desiccation and to understand the role of antioxidant systems to ensure survival of living beings when in the anhydrobiotic state.
Even though desiccation does not seem to have an effect on tardigrade longevity, damages are accumulated in proportion to the time spent in the desiccated state, leading to animal death. High temperatures, high humidity and high oxygen partial pressure are all factors that negatively affect tardigrade survival during long-term anhydrobiosis since they are involved in the production of oxidative stress. These abiotic conditions also directly influence the time required by animals to recover active life after a period of desiccation. Experimental studies produced evidence that enzymes (e.g. peroxidases, catalases, superoxide dismutase) and antioxidants (e.g. glutathione and carotenoids) represent a key group of molecules required for desiccation tolerance in tardigrades. The action of these molecules emphasises the need for redox balancing in anhydrobiotic tardigrades
Dry up and survive: the role of antioxidant defences in anhydrobiotic organisms
Full text linkAlthough the evolution of life has turned oxygen into a vital chemical for aerobic organisms, this element can also have deleterious effects on living systems through the production of oxidative stress. This is a process resulting from an imbalance between the excessive production of Reactive Oxygen Species (ROS) and the limited action of antioxidant defences. It is a particularly harmful health risk factor, involved in the development of several chronic human pathologies and believed to play a major role in the ageing process. Consequently aerobic metabolism needs a stringent control of ROS. Water too is essential for life, but some organisms widespread throughout nature have the ability to survive complete desiccation by entering an anhydrobiotic state. The loss of water induces changes in metabolism, cell membrane organization, and molecular composition. In the anhydrobiotic state, high temperatures, high humidity, light exposure, and high oxygen partial pressure negatively affect organism survival and directly influence the time required to reactivate the metabolism after a period of desiccation. These abiotic factors induce damages that are accumulated in proportion to the time spent in the desiccated state, potentially leading to organism death. Oxidative stress seems to be one of the most deleterious damages due to water depletion, therefore anhydrobiosis also needs a stringent control of ROS production. Anhydrobiotic organisms seem to apply two main strategies to cope with the danger of oxygen toxicity, namely an increased efficiency of antioxidant defences and a metabolic control of both energy-production and energy-consuming processes. Experimental studies provide evidence that antioxidant defences such as ROS scavenging enzymes (e.g. peroxidases, catalases, superoxide dismutase, glutathione peroxidases) and other molecules (e.g. glutathione, carotenoids, vitamins C and E) represent a key group of molecules required for desiccation tolerance in anhydrobiotic organisms. The action of these molecules emphasises the need for redox balancing in anhydrobiotic organisms including tardigrades and chironomid larvae
Gli animali de "Le avventure di Pinocchio"
No full textThe aim of this paper is to increase our knowledge on the about 60 different kind of animals cited in the literary work “Le avventure di Pinocchio”. Through brief and fleeting apparitions, these animals have the task of supporting the symbolic language of the narrative because advisors, guides, barriers and helpers of Pinocchio, or as caricature of the institutions. The knowledge of the animals diversity characterizing the “Le avventure di Pinocchio” is analyzed considering their geographical distribution and colonized habitats. Moreover, the metaphoric meaning of the animals is also considered
Spermatozoon morphology of three species of Hypsibiidae (Tardigrada, Eutardigrada)and phylogenetic evaluation
No full textThe spermatozoan ultrastructure of the gonochoristic eutardigrades Pseudobiotus megalonyx, Ramazzottius tribulosus and Ramazzottius oberhaeuseri (Hypsibiidae, Hypsibiinae) are described and illustrated. The two species of the same genus have very similar spermatozoa, whereas the two genera differ widely in male gamete organization. The testicular spermatozoon of Pseudobiotus has a thread-like configuration and is made up of a small comma-shaped acrosome, a helical nucleus and a tail with terminal tuft; no middle piece or neck and mitochondria were observed. The testicular spermatozoon of Ramazzottius shows an evident rod-shaped acrosome, a cork-screwshaped nucleus and a short tubular middle piece containing a mitochondrial sleeve; moreover, the tail splits terminally into a tuft. Functional considerations and phylogenetic comparisons are made on the basis of sperm morphology
Ramazzottius semisculptus, nuova specie di Hypsibiidae (Eutardigrada).
No full textGli autori descrivono una nuova specie di Eutardigrada, Ramazzottius semisculptus, la cui cuticola presenta una scultura (costituita da tubercoli poligonali) appena visibile e limitata alla estremità caudale del corpo; talvolta essa è completamente liscia. Le uova sono deposte libere e sono provviste di piccole sporgenze coniche, lisce, con la base frastagliata
Rearing tardigrades: Results and problems
No full textWe report our first results of attempts to rear four species of eutardigrades inhabiting different substrates, feeding on different kinds of food and characterized by different sexual conditions and modes of reproduction. Attempts were carried out to follow individual terrestrial carnivorous (Macrobiotus richtersi, M. joannae) and limnic herbivorous (Diphascon cf. scoticum; Isohypsibius monoicus) species. Carnivorous leaf litter-dwelling species were reared in small dishes containing agar as substrate and bacteriophagous nematodes as food. Five generations were obtained with the triploid. thelytokous strain of M. richtersi, whereas three generations were obtained with the hermaphrodite species M. joannae, Diphascon cf. scoticum and I. monoicus were reared in small dishes containing algae as food and substrate. Several generations were obtained for both species. Males were never found in D. cf. scoticum and I. monoicus was hermaphroditic. Specimens isolated from hatchings were maintained and reproduced in both species, demonstrating parthenogenesis in the first one and self-fertilization in the latter. Consideration of the problems and on the future applications of tardigrade rearing are discussed
First evidence of achiasmatic male meiosis in the water bears Richtersius coronifer and Macrobiotus richtersi (Eutardigrada, Macrobiotidae)
Full text linkChromosome 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
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