Anaerobic bacteria in the gut of terrestrial isopod crustaceanPorcellio scaber

Anaerobic bacteria from Porcellio scaber hindgut were identified and, subsequently, isolated using molecular approach. Phylogenetic affiliation of bacteria associated with the hindgut wall was determined by analysis of bacterial 16S rRNA gene sequences which were retrieved directly from washed hindguts of P. scaber. Sequences from bacteria related to obligate anaerobic bacteria from genera Bacteroides and Enterococcus were retrieved, as well as sequences from 'A1 subcluster' of the wall-less mollicutes. Bacteria from the genus Desulfotomaculum were isolated from gut wall and cultivated under anaerobic conditions. In contrast to previous reports which suggested the absence of anaerobic bacteria in the isopod digestive system due to short retention time of the food in the tube-like hindgut, frequent renewal of the gut cuticle during the moulting process, and unsuccessful attempts to isolate anaerobic bacteria from this environment our results indicate the presence of resident anaerobic bacteria in the gut of P. scaber, in spite of apparently unsuitable, i.e. predominantly oxic, conditions.     

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     

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.     

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     

Adaptation to cadmium in three populations of the isopod Porcellio scaber

• 1.1. First-generation laboratory animals of three populations of the isopod Porcellio scaber, collected from a reference wood, a zinc smelter area and a lead mine site, were compared with respect to effects of Cd.
• 2.2. All populations reacted differently to Cd-contaminated food: increased Cd concentrations in the food resulted in decreased consumption and growth for the reference isopods; mine isopods were not affected by Cd and for the smelter animals Cd stimulated growth at an intermediate concentration.
• 3.3. Since Cd concentrations in the isopod did not differ between populations, adaptation is probably based on an increased detoxification capacity.
• 4.4. The assimilation of Cd did not affect the Cu or Zn content of the isopods although the adapted isopods regulated their Cu content on a lower level than reference isopods.

     

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     

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.     

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.     

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     

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.     

Uropod and lateral plate glands of the terrestrial isopod Porcellio scaber Latr. (Oniscidae,Crustacea): An ultrastructural study

Lateral plate and uropod glands are composed of a binucleated gland cell, a ramified intermediate cell, and an elongated duct cell. The gland cell is divided into several lobes and forms numerous short processes in its periphery. The cytoplasm contains many secretory granules. The granules release their content into the intercellular collecting ducts between the gland cell and the branched extensions of the intermediate cell. The collecting ducts merge into a funnel-shaped space surrounded by the intermediate cell. The duct cell is lined by a cuticular intima and contains long striated bundles of fibrils. The duct cell consists of two different regions. The proximal region is characterized by microvilli on the luminal side and contains many organelles. In the distal region microvilli are lacking and organelles are scarce. Structurally, the uropod and lateral plate glands differ in the number of components within the granules. This is in accordance with the differences in the characteristics of the secretory products of the two gland types. The morphology of the glands, particularly the peripheral position of the collecting system, is unique among exocrine glands of arthropods. J. Morphol. 233:183–193, 1997 © 1997 Wiley-Liss, Inc.     

The energetics of reproduction and parental care in the terrestrial isopod Porcellio laevis

Parental care is a behavioral strategy that contributes to increased fitness of progeny. Among terrestrial arthropods, many isopods provide extensive parental care. Few studies have quantified the underlying cost of parental care in terms of energy. We used the terrestrial woodlouse Porcellio laevis (Latreille) as a study model to examine how energetic acquisition and expenditure in females is affected during the incubation period and how parental care affects energy balance in this species. We determined the basic reproductive biology (i.e. fecundity, reproductive output, egg volume, egg loss), energy expenditure (i.e. metabolic rate), and energy acquisition (i.e. food consumption, digestibility) of ovigerous females in different stages of embryonic development. Non-ovigerous females were used as the control group. Our results show that P. laevis displays variability in life-history traits compared with populations from other zones around the world. Ovigerous females exhibited a lower ingestion rate and lower digestibility than control females, thus indicating a lower capacity for energy acquisition. Furthermore, energy expenditure was higher in ovigerous females when compared to non-ovigerous females. In particular, females in early embryonic development stored 5.1-fold less daily energy than females without eggs.

The results presented here show that the parental care provided by female P. laevis is energetically costly. Overall, our work brings us much closer to understanding the proximate mechanisms of the costs of parental care in terrestrial isopods. Both proximal mechanisms and consequences of providing care on future reproduction, should be considered in explaining the evolution of parental care.     

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.     

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.     

Phoresy of the entomopathogenic nematode Heterorhabditis marelatus by a non-host organism, the isopod Porcellio scaber

Entomopathogenic nematodes are widespread in nature and commonly used in the biological control of insect pests. However, we understand little about how these organisms disperse. We show in a laboratory setting that the entomopathogenic nematode Heterorhabditis marelatus is phoretically dispersed by a non-host organism, the isopod Porcellio scaber. These species both inhabit tunnels excavated in the roots and lower stems of bush lupine (Lupinus arboreus) by the nematodes' primary prey, larvae of the ghost moth Hepialus californicus. Phoretic dispersal via P. scaber may play a role in the metapopulation dynamics of this nematode.     

"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.     

Effects of starvation on body composition and cold tolerance in the collembolan Orchesella cincta and the isopod Porcellio scaber

The effects of long-term starvation on the body composition of the isopod Porcellio scaber (Latreille) and the collembolan Orchesella cincta (L.) were studied, by determining the body composition in starved and fed animals. A period under summer conditions (19 degrees C, 75% RH and L/D 16/8 photoperiod), was followed by a period under winter conditions (5 degrees C, 75% RH and LD 6/18 photoperiod). O. cincta was held under summer conditions for 3weeks, during which its protein and lipid content decreased, while its water content increased. In P. scaber, the same occurred during the 6weeks they were kept under summer conditions. During subsequent weeks under winter conditions, changes in cold tolerance of the animals were investigated. Cold tolerance and haemolymph osmolality were measured once a week. Starved animals had lower cold tolerance than fed ones. For P. scaber a decreased haemolymph osmolality was found in starved animals compared to fed ones. This is assumed to be caused by a combination of the consumption of carbohydrates out of the haemolymph and of protein reserves and the accumulation of body water. O. cincta appeared to be capable of osmoregulation, as haemolymph osmolality did not differ between starved and fed animals, despite differences in body water content. Decreased cold tolerance in starved animals of both species may be caused by increased water content or, more probably, by the decrease in reserves needed to produce cryoprotective substances.