The ionic hemolymph composition of the terrestrial isopod Porcellio scaber Latr. during molt

We analyzed the ionic composition of the hemolymph of Porcellio scaber in four different stages of the molt cycle using capillary electrophoresis and calcium selective mini- and microelectrodes. The main ions in the hemolymph were K⁺, Ca²⁺, Na⁺, Mg⁺, and Cl⁻. The values for total calcium obtained by means of capillary electrophoresis and calcium selective minielectrodes did not differ significantly from each other. In situ measurements of the free Ca²⁺ concentration ([Ca²⁺]) by means of calcium-selective microelectrodes indicated that Ca²⁺ is not bound in the hemolymph. During molt the [Ca²⁺] is significantly larger than during intermolt. The [Ca²⁺] increased by 13%, 19% and 18% during premolt, intramolt, and postmolt, respectively. The concentration of the other cations and of Cl⁻ decreased significantly between premolt and intramolt. Thus, the rise of the [Ca²⁺] in the hemolymph is not due to a general increase in all ions, but rather to the resorption of cuticular calcium. Furthermore, the results suggest that K⁺, Na⁺, Mg⁺, and Cl⁻are extruded from the hemolymph during and/or after posterior ecdysis. Accepted: 5 August 1997     

Ultrastructural changes of the anterior and posterior sternal integument of the terrestrial isopod Porcellio scaber Latr. (Crustacea) during the moult cycle

The ultrastructure of the anterior (ASE) and posterior sternal epithelium (PSE) was investigated during the biphasic moult cycle. During early premoult the sternal epithelial cells increase in size, accumulate huge amounts of glycogen, and increase the abundance of cellular organelles. CaCO(3) deposit formation begins before the secretion of the epicuticle in the anterior sternal integument and continues through the secretion of the first exocuticular layers. The deposition of cuticle is delayed in the ASE until the CaCO(3) deposit is fully resorbed between the anterior and posterior moult. The development of the interstitial network (IN), which enormously increases the basolateral compartment of the plasma membrane, starts at the beginning of the exocuticle deposition. During CaCO(3) deposit formation and resorption the volume fraction of the mitochondria is much larger in the ASE than in the PSE, although the cuticle is secreted faster in the posterior integument. The results suggest that the exocuticular and epicuticular layers are permeable to calcium and probably also carbonate ions; that the IN is required during late premoult, when CaCO(3) deposition is accelerated, but not during early CaCO(3) deposition; and that active mechanisms contribute to transepithelial ion transport during CaCO(3) deposit formation and resorption.     

Morphology,morphometry and ultrastructure of the maxillary gland of the terrestrial isopod Porcellio scaber (Crustacea,Oniscidea)

Summary The ultrastructure of the maxillary gland of the terrestrial isopod Porcellio scaber is described. The gland is composed of an end sac, an excretory duct and a terminal duct which opens by a valve at the base of maxilla 2. An epithelium of podocytes in the end sac enables passive ultrafiltration by haemolymph pressure. The excretory duct shows ultrastructural adaptations to secretion and resorption. SEM micrographs reveal the location and the morphology of the valve at the excretory pore. A model reconstructed from serial sections allowed the calculation of morphometric data of the gland. The ultrafiltration area of the end sac and the area of resorption and secretion of the excretory duct amount to 0.091 and 0.157 cm² per 1 g of fresh body weight, respectively. The total volume of the gland is calculated to be 0.04 mm³ in a specimen of 13.7 mm length. In comparison with the marine species Mesidotea entomon, the relative areas for ultrafiltration and resorption of the gland of P. scaber are more than twice as large as the corresponding areas of the marine species. This relative enlargement of the gland in P. scaber and the form of the valve at the excretory pore are seen as adaptations to terrestrial life.     

The ultrastructure of the androgenic gland in Porcellio scaber Latr. (terrestrial isopods)

Summary This paper presents the normal ultrastructural features of the androgenic gland in Porcellio scaber. It describes the changes in the organelles of its cells through the course of the secretory cycle, which terminates with the regression and destruction of these holocrine glandular cells. As products of this activity, the electron-opaque bodies (granules, lysosomes, agglomerates) and clear substances accumulate in the cytoplasm. With the destruction of the cell membrane, the entire cell content passes into the spaces of the haemocoele. The morphological modifications of the mitochondria and rough endoplasmic reticulum are the most striking changes.

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Résumé Les auteurs présentent, dans ce travail, les aspects ultrastructuraux normaux de la glande androgène chez l'oniscoïde Porcellio scaber. On montre, par des phases successives, les modifications morpho-fonctionnelles des organites cellulaires jusqu'à la fin du cycle sécrétoire, qui finit par la dégradation et la destruction des cellules glandulaires, dont la fonction est de type holocrin. Comme produits de cette activité, des corps éléctrono-opaques (grains, agglomerats, lysosomes) et des substances claires apparaissent dans le cytoplasme. Par la destruction de la membrane plasmique, tout le contenu cellulaire est éliminé dans les espaces haemocoeliens, soit par écoulement soit par fragments. Le RE et le chondriome subissent les modifications les plus spectaculaires.

     

Prolonged feeding of terrestrial isopod (Porcellio scaber, Isopoda, Crustacea) on TiO (2) nanoparicles. Absence of toxic effect

Nanoparticles of titanium dioxide are one of most widely used nanomaterials in different products in everyday use and in industry, but very little is known about their effects on non- target cells and tissues. Terrestrial isopods were exposed to food dosed with nano-TiO(2) to give final nominal concentration 1000 and 2000 μg TiO(2)/g dry weight of food. The effects of ingested nano-TiO(2) on the model invertebrate Porcellio scaber (Isopoda, Crustacea) after short-term (3 and 7 days) and prolonged (14 and 28 days) dietary exposure was assessed by conventional toxicity measures such as feeding rate, weight change and mortality. Cell membrane destabilization was also investigated. No severe toxicity effects were observed after 3, 7, 14 or 28 days of dietary exposure to nano-TiO(2), but some animals, particularly those exposed to lower concentrations of nanoparticles, had severely destabilized digestive cell membranes. It was concluded that strong destabilization of the cell membrane was sporadic, and neither concentration- nor time-related. Further research is needed to confirm this sporadic toxic effect of nanoparticles.     

Heavy metals in the terrestrial isopod Porcellio scaber latreille. I. Histochemical and ultrastructural characterization of metal-containing lysosomes

Different populations of metal-loaded and uncontaminated Porcelio scaber Latreille were studied. Combined light and electron microscopial methods as well as X-ray microanalysis were applied for localization and characterization of intracellular sites of metal deposition within the small cells of hepatopancreas. By means of cytochemistry and X-ray microanalysis it was shown that membrane-limited vesicles are important sites of deposition for lead, copper, zinc and probably smaller amounts of cadmium. The vesicles also contained phosphorus. They are identical with the reported cuprosomes and belong to the lysosomal system. In addition, considerable amounts of lead, copper, and cadmium were found in small structures outside of membrane-limited organelles.Abbreviations EDX energy-dispersive X-ray - P. scaber Porcellio scaber - STEM scanning transmission electron microscope - TEM transmission electron microscope - v volume - wt weight     

Ultrastructural study of yolk formation in Porcellio scaber Latr. (Isopoda)

Two types of yolk are formed in the developing oocytes of a terrestrial crustacean, Porcellio scaber. The intra-oocytic yolk, arises through autosynthesis, and the extra-oocytic yolk, is derived from micropinocytosis. the so-called disc shaped bodies, which occur in large numbers within the cisternae of a branched system of endoplasmic reticulum, are precursors of the intra-oocytic uolk. Dictyosomes are not involved in yolk formation in this species. Thus, the vitellogenesis of Porcellio scaber occurs in a manner analogues to that described in the aquatic crustaceans, which indicates that environmental factors have relatively little effect on this process.     

Analysis of CaCO3 deposit formation and degradation during the molt cycle of the terrestrial isopod Porcellio scaber (Crustacea,Isopoda)

Terrestrial isopods store cuticular calcium in large sternal deposits composed of an amorphous CaCO(3) compound. A large part of the deposits consists of numerous small spherules that increase the exposed surface to facilitate resorption of CaCO(3) during cuticle mineralization. It is not known how these spherules are formed and how they are dissolved. This paper presents for the first time an analysis of ultrastructural changes occurring in the sternal CaCO(3) deposits of a terrestrial isopod during their formation and degradation. Our results indicate that formation of the spherules takes place in a specialized aggregation zone, in which 10- to 30-nm-thick granules form agglomerations that then increase in size to form spherules that reveal a concentric growth pattern. Degradation of the deposits occurs in a manner that exposes a maximum of surface area on all levels of their structural organization.     

Cold adaptation of the terrestrial isopod,Porcellio scaber,to subnivean environments

The terrestrial isopod, Porcellio scaber, was susceptible to subzero temperature: both freezing and chilling were injurious. The level of cold hardiness against chilling and freezing showed different patterns in their seasonal variation. The lower lethal temperature causing 50% mortality, an indicator of the tolerance to chilling, ranged from-1.37°C in August to-4.58°C in December. The whole body supercooling point, the absolute limit of freeze avoidance, was kept at about-7°C throughout the year. The winter decrease in lower lethal temperature was concomitant with an accumulation of low molecular weight carbohydrates which are possible protective reagents against chilling injury, whereas the less seasonally variable supercooling point seemed to be associated with the year-round presence of gut content. Food derivatives may act as efficient ice nucleators. The different trend in seasonal changes between lower lethal temperature and supercooling point may be related to the microclimate of the hibernacula in subnivean environments, where the winter temperature became lower than the lower lethal temperature in the summer active phase, but remained higher than the summer supercooling point.Abbreviations LLT₅₀ lower lethal temperature inducing 50% mortality - SCP supercooling point - T _a ambient air temperature - T _s soil surface temperature     

"Candidatus Bacilloplasma," a novel lineage of Mollicutes associated with the hindgut wall of the terrestrial isopod Porcellio scaber (Crustacea: Isopoda)

Pointed, rod-shaped bacteria colonizing the cuticular surface of the hindgut of the terrestrial isopod crustacean Porcellio scaber (Crustacea: Isopoda) were investigated by comparative 16S rRNA gene sequence analysis and electron microscopy. The results of phylogenetic analysis, and the absence of a cell wall, affiliated these bacteria with the class Mollicutes, within which they represent a novel and deeply branched lineage, sharing less than 82.6% sequence similarity to known Mollicutes. The lineage has been positioned as a sister group to the clade comprising the Spiroplasma group, the Mycoplasma pneumoniae group, and the Mycoplasma hominis group. The specific signature sequence was identified and used as a probe in in situ hybridization, which confirmed that the retrieved sequences originate from the attached rod-shaped bacteria from the hindgut of P. scaber and made it possible to detect these bacteria in their natural environment. Scanning and transmission electron microscopy revealed a spherically shaped structure at the tapered end of the rod-shaped bacteria, enabling their specific and exclusive attachment to the tip of the cuticular spines on the inner surface of the gut. Specific adaptation to the gut environment, as well as phylogenetic positioning, indicate the long-term association and probable coevolution of the bacteria and the host. Taking into account their pointed, rod-shaped morphology and their phylogenetic position, the name "Candidatus Bacilloplasma" has been proposed for this new lineage of bacteria specifically associated with the gut surface of P. scaber.     

An investigation of the surface of the cuticle and associated sensory structures of the terrestrial isopod, Porcellio scaber

The exoskeletal surface of the body of the terrestrial isopod, Porcellio scaber has been examined with the scanning electron microscope as part of a study of the structural changes associated with the transition from sea to land in the Isopoda. No sexual differences are apparent. The dorsal cuticular surface is characterized by large tubercles, minute plaques and pits, separated by amorphous areas. Apart from the eyes the only structures of apparent sensory function are relatively large setae which occur near the antero-lateral and posterolateral edges of each epimeron, and sensilla squamiformia (tricorns). Tricorns are extremely numerous on the dorsal surface and appear to be formed from the fusion of a plaque and a sensillum which arises from a pit. Much of the ventral body surface is covered with closely-set plaques, tricorns being restricted to the epimera. Along the sides of the mid-ventral sternal groove occur numerous small tubercles each surmounted by a single seta. Similar, though smaller structures are found in a single row along the outer edge of the epimera. The water capillary system of this species is formed from spines which arise from plaques around the pereopodal sockets and along the junctions between the epimera and sternites. Most of the sensilla described appear to be mechanosensory and are probably associated with the thigmokinetic and proprioceptive responses of the woodlouse.     

Membrane particle distribution in the sternal epithelia of the terrestrial isopod Porcellio scaber latr. (Crustacea, oniscidea) during CaCO(3) deposit formation and resorption, a freeze-etch analysis.

The anterior sternal epithelium of terrestrial isopods transports cuticular Ca(2+) to and from large sternal CaCO(3) deposits. We analyzed the anterior and posterior sternal epithelium by the means of the freeze-etch technique and measured the size distribution and density of intramembrane particles (IMPs) during three different molting stages. At least three IMP size classes around 4.5, 7.7, and 9.4 nm can be distinguished on the P-face of the apical and basolateral plasma membrane. An additional size class of around 12.8 nm is restricted to the apical compartment. In the anterior sternal epithelium, the density of these large particles changes by a factor of 1.9 during the molt cycle, suggesting a role in CaCO(3) formation and/or resorption. The density of the smaller IMPs rises transiently by a factor of 1.3 in the posterior sternal epithelium only. The IMP density of the basolateral plasma membrane increases significantly by a factor of 1.4 and 1.3 in the anterior and posterior sternal epithelia, respectively. The results indicate that increases in the IMP density contribute to the differentiation to an increased transport activity during the cyclic enlargements of the plasma membrane surface area in the anterior sternal epithelium.     

An intra-species demonstration of the independence of distance and time in turn alternation of the terrestrial isopod, Porcellio scaber

In a study of turn alternation in the terrestrial isopod Porcellio scaber (woodlouse), smaller individuals (<11 mm long) took significantly longer to traverse a 60-mm open-ended post-forced-turn runway following a 90 degrees forced turn, than larger subjects (>11 mm long). However, there were no significant differences between the two groups in their probability of alternating, or in the magnitude of alternating turns as reflected in the size of the free-turn angles they turned on emerging from the runway. Nor was there a significant relationship for either group between the time taken to traverse the runway and either the probability of alternating or the size of a free-turn angle. In a second experiment, significant alternation occurred after woodlice emerged from runways that were 30 and 60 mm long, but not when they were 100 or 145 mm long. Their free-turn angles also became smaller as the runway length increased. Overall, the results of the three experiments supported the long-held view that, for reasons not yet understood, distance and time cannot necessarily be equated in the determination of invertebrate turn alternation.     

Early reproduction and increased reproductive allocation in metal-adapted populations of the terrestrial isopod Porcellio scaber

Organisms inhabiting metal-contaminated areas can be stressed by metal exposure and are possibly subject to selection, resulting in increased metal tolerance and changes in growth and/or reproduction characteristics. In a previous study it was found that in the terrestrial isopod Porcellio scaber, sampled from the vicinity of a zine smelter, the body size was small and the brood size was large compared to isopods from a reference area. To assess whether these differences were due to genetic differentiation between strains, isopods collected from a reference wood, a zinc smelter area and a lead mine were cultured on non-polluted food, while growth, reproduction and metal concentrations were studied in first and second laboratory generations. The isopods from the three populations differed in age and weight at first reproduction, although there were hardly any differences in growth. The females of the mine and the smelter population started to reproduce earlier, at a lower weight, which resulted in fewer young per female. However, reproductive allocation (=wight of young relative to the weight of the mother) was higher in mine and smelter isopods. We conclude that the isopods at the metal-contaminated sites have been selected for early reproduction and increased reproductive allocation. The results indicate that populations inhabiting metal-polluted sites have probably undergone evolutionary changes. This study showed that growth and reproduction characteristics of different populations under laboratory conditions may provide information on selection processes in the field.     

Microplastic ingestion affects hydrogen production and microbiomes in the gut of the terrestrial isopod Porcellio scaber

Microplastic (MP) is an environmental burden and enters food webs via ingestion by macrofauna, including isopods (Porcellio scaber) in terrestrial ecosystems. Isopods represent ubiquitously abundant, ecologically important detritivores. However, MP-polymer specific effects on the host and its gut microbiota are unknown. We tested the hypothesis that biodegradable (polylactic acid [PLA]) and non-biodegradable (polyethylene terephthalate [PET]; polystyrene [PS]) MPs have contrasting effects on P. scaber mediated by changes of the gut microbiota. The isopod fitness after an 8-week MP-exposure was generally unaffected, although the isopods showed avoidance behaviour to PS-food. MP-polymer specific effects on gut microbes were detected, including a stimulation of microbial activity by PLA compared with MP-free controls. PLA stimulated hydrogen emission from isopod guts, while PET and PS were inhibitory. We roughly estimated 10⁷ kg year⁻¹ hydrogen emitted from the isopods globally and identified their guts as anoxic, significant mobile sources of reductant for soil microbes despite the absence of classical obligate anaerobes, likely due to Enterobacteriaceae-related fermentation activities that were stimulated by lactate generated during PLA-degradation. The findings suggest negative effects of PET and PS on gut fermentation, modulation of important isopod hydrogen emissions by MP pollution and the potential of MP to affect terrestrial food webs.     

Microscopic anatomy and ultrastructure of the stomach of Porcellio scaber (Crustacea,Isopoda)

Summary From the micromorphological viewpoint, the stomach is by far the most complicated part of the digestive tract of Porcellio scaber. All parts are shown in electron micrographs. The simplest inner surface of the stomach is the dorsal part, which has an unpaired flap directed posteriorly (lamella dorsalis). The lateral walls carry the lateralia, superolateralia and lamellae annulares. The most complicated region of the stomach is the ventral surface with its anterior primary filter, the adjacent masticatory areas, the posterior secondary filter on the lateral sides of the inferomedianum and the inferolateralia. Ingested food can be filtered twice: first on the primary filter and then on the secondary filter. The digestive fluid secreted in the midgut glands can be conveyed on the same route as the filtrate of the gastric juice, but in the other direction. The posterior part of the stomach is wrapped by a ring-shaped fold of the anterior hindgut, thus making seven epithelia closely apposed to each other.     

Heavy metals in the terrestrial isopod Porcellio scaber Latreille. II. Subcellular fractionation of metal-accumulating lysosomes from hepatopancreas

Two populations of metal contaminated Porcellio scaber Latreille were studied: one consisting of animals that had been fed heavy metals in the laboratory for several months, and one from a metal-polluted site in the field (Braubach, FRG). Density gradient centrifugation was performed on hepatopancreas homogenates in order to identify cellular fractions and their association with lead, copper and cadmium. Marker enzymes were used for localisation of cellular fractions in the density gradient. Two lysosomal fractions, called the light and heavy fraction, were separated. They contained mainly lead, but also copper and some cadmium.Abbreviations AP acid phosphatase - ER endoplasmic reticulum - LDH lactic dehydrogenase - MDH malic dehydrogenase - NADH nicotinamide adenine dinucleotide - P. scaber Porcellio scaber     

Exoskeletal cuticle differentiation during intramarsupial development of Porcellio scaber (Crustacea: Isopoda)

Exoskeletal crustacean cuticle is a calcified apical extracellular matrix of epidermal cells, illustrating the chitin-based organic scaffold for biomineralization. Studies of cuticle formation during molting reveal significant dynamics and complexity of the assembly processes, while cuticle formation during embryogenesis is poorly investigated. This study reveals in the terrestrial isopod Porcellio scaber, the ultrastructural organization of the differentiating precuticular matrices and exoskeletal cuticles during embryonic and larval intramarsupial development. The composition of the epidermal matrices was obtained by WGA lectin labelling and EDXS analysis. At least two precuticular matrices, consisting of loosely arranged material with overlying electron dense lamina, are secreted by the epidermis in the mid-stage embryo. The prehatching embryo is the earliest developmental stage with a cuticular matrix consisting of an epicuticle and a procuticle, displaying WGA binding and forming cuticular scales. In newly hatched marsupial larva manca, a new cuticle is formed and calcium sequestration in the cuticle is evident. Progression of larval development leads to the cuticle thickening, structural differentiation of cuticular layers and prominent cuticle calcification. Morphological characteristics of exoskeleton renewal in marsupial manca are described. Elaborated cuticle in marsupial larvae indicates the importance of the exoskeleton in protection and support of the larval body in the marsupium and during the release of larvae in the external environment.