Oniscus Asellus Research Articles

Intraspecific variation in the terrestrial isopod Oniscus asellus Linnaeus, 1758 (Crustacea: Isopoda: Oniscidea)

A study of intraspecific variation in one of the most widespread and abundant terrestrial isopods in Europe, Oniscus asellus is presented. It is concluded that previous attempts to describe intraspecific taxa in this species are invalid, but that the species is clearly divisible into two subspecies which differ in a number of features, including male sexual modifications. The nominal subspecies, Oniscus asellus asellus Linnaeus, 1758, is described in detail, and a neotype, collected from Uppsala, Sweden, where Linnacus lived and worked, is designated. Oniscus asellus occidentalis ssp. nov. is also described, and reported as occurring in the far west of the species' range, in the British Isles, Ireland and France. Characters useful in distinguishing these two taxa are indicated and figured. Differences in the ecology of the two taxa are also noted, occidentalis appearing to be a relict Atlantic taxon, largely restricted to damp woodland. The existence of populations intermediate between asellus and occidentalis is noted, and the features of these populations discussed in detail. A combination of geographical, environmental and laboratory breeding data suggest that these intermediates arise through hybridization between the two subspecies, this process of hybridization being accelerated by human activity, which brings the two taxa into frequent contact. It is suggested that Oniscus asellus may provide an excellent model system for the study of the dynamics of hybrid zones.

Changes in Haemolymph Ecdysteroid Levels and Cns Contents of Crustacean Cardioactive Peptide-Immunoreactivity During the Moult Cycle of the Isopod Oniscus Asellus

By use of newly developed enzyme immunoassays for ecdysteroids (ECD) and crustacean cardioactive peptide (CCAP) it was found (1) that in the isopod Oniscus asellus a peak occurs of hemolymph (HL)-ECD contents in prcmoult stages followed by a second but smaller peak 1 h after posterior ecdysis, and (2) that concomitantly with a drop in the first ECD-peak, CCAP-contcnts of the ventral nerve cord rise tenfold basal level around posterior ecdysis. This suggests that CCAP plays a role in isopod moulting processes.

Terrestrial life in isopods: evolutionary loss of gas-exchange and survival capability in water

Survival and oxygen uptake in air and water were investigated in four species of terrestrial isopods, Armadillidium vulgare Latreille, 1804, Porcellio scaber Latreille, 1804, Oniscus asellus Linné, 1758, and Ligia pallasii Brandt, 1833, to compare the degree of vestigial adaptation to aquatic existence versus adaptation to terrestrial existence. Most submerged A. vulgare, P. scaber, and O. asellus died by 18 h, whether in fresh water or isosmotic seawater. Ligia pallasii lived for almost 2 d in fresh water and for at least 25 d in seawater (none died during this time). Oxygen uptake in water was 44 – 66% that in air for the three fully terrestrial species, and 160% that in air for the semiterrestrial L. pallasii. Oxygen consumption of submerged A. vulgare (representative of fully terrestrial forms) declined to 50% after 14 h and to 17% by 24 h, by which time the animals were clinically dead. In comparison, L. pallasii's aquatic oxygen consumption was maintained at normal or higher levels for at least 3 d. All species could survive several hours of immersion in fresh water, sufficient to withstand temporary rain deluge. Ligia pallasii's superior capabilities to survive and respire in seawater reflect its greater similarity to aquatic ancestors, and an evolutionary series showing progressive decline in survival and gas-exchange capability in water would be as follows: L. pallasii > O. asellus > P. scaber ≥ A. vulgare.

The isopod Porcellio scaber as a monitor of the bioavailability of metals in terrestrial ecosystems: towards a global ‘woodlouse watch’ scheme

Concentrations of cadmium, copper, lead and zinc were determined in nitric acid digests of the terrestrial isopods (woodlice) Porcellio scaber and Oniscus asellus, and soil collected from 48 sites in a region in S.W. England contaminated by earlier mining activity and ongoing aerial fallout from a smelting works. For all four metals, closer correlations were obtained between the two species of isopods than between soil and isopods. Thus, levels of metals in Oniscus asellus could be predicted more accurately from those in Porcellio scaber than from concentrations in soil in the region. A table is included that allows the ‘level of contamination’ of a site to be assessed based on concentrations of metals in a pooled sample of 12 adult Porcellio scaber. Preliminary correlations are also presented between Porcellio scaber, Oniscus asellus and nine other species of terrestrial isopods. The worldwide distribution of Porcellio scaber (which has been introduced to most countries) makes this woodlouse an ideal candidate for monitoring the bioavailability of metals to soil and leaf litter invertebrates. A global ‘woodhouse watch’ is proposed, similar to the ‘mussel watch’ scheme that has proved so successful in the marine environment.

Effects of benzo[ a]pyrene on survival, growth and energy reserves in the terrestrial isopods Oniscus asellus and Porcellio scaber

Two terrestrial crustaceans were exposed for 9 weeks to benzo[ a]pyrene (BaP) in their food at 0 (control, n = 30); 3.16; 10; 31.6; 100 and 316 μg BaP/g dry wt. ( n = 24). Porcellio scaber and Oniscus asellus did not differ much in their sensitivity for BaP: in both species growth was affected at 100 and 316 μg/g (NOEC = 31.6 μ/g) At 316 μ/g the effect of BaP on O. asellus was more pronounced: growth was reduced by 58% versus 26% in P. scaber. In both species the energy reserves were reduced at 316 μg/g: in O. asellus the lipid pool seemed reduced and in P. scaber the protein pool. The apparent difference in response between the species with respect to energy reserves and growth may be related to differences in size: initial fresh weight of P. scaber was 8.52 mg (S.D. = 2.85), of O. asellus 2.82 mg (S.D. = 0.59). O. asellus survival was reduced to 71% at 316 μg/g, whereas 98% survived at the other concentrations. Overall survival in P. scaber was 76%. The results show that BaP may pose a threat to terrestrial invertebrates, although the effective concentrations are relatively high.

Hemolymph protein patterns and coprophagous behaviour inOniscus asellusL. (Crustacea, Isopoda)

Summary The ingestion of an animal's own faeces (coprophagy) is a common phenomenon in terrestrial isopods. In the present investigation the influence of withholding faeces on growth and on the hemolymph protein composition of different life stages of the wood-louse Oniscus asellus was assessed. Juvenile Oniscus asellus reared without access to their faeces suffered severely under this treatment. Their gain in body mass was significantly lower than that in the control group. In contrast, the effect of non-coprophagous rearing was moderate or not detectable in subadult and adult individuals, respectively. No correlation occurred between coprophagy and survival rates in all test groups. The relative content of hemocyanin in the hemolymph of coprophagous as compared to non-coprophagous juveniles showed no significant differences. The same was true for the total protein content of the hemolymph in relation to the body mass. However, the relative amount of a distinct glycoprotein, which typically disappears un...

A daily cycle of apocrine secretion by the B cells in the hepatopancreas of terrestrial isopods

The ultrastructure of the two cell types of the hepatopancreas of the terrestrial isopods Oniscus asellus and Porcellio scaber was examined at hourly intervals in animals habituated to a 16 h light: 8 h dark cycle. The ultrastructure of the B cells undergoes substantial changes which are repeated every 24 h. This 'B cell cycle' can be divided into two stages. During the first, 'extrusive' stage, which begins about 1 h before the onset of the light period, the contents of the B cells apical to the nuclei are voided into the lumen of the hepatopancreas. The second, 'restitutive,' stage begins about 10 h after the onset of the light cycle. The B cells swell in size by the accumulation of the new material until the next extrusive stage. The ultrastructural appearance of the S cells was similar at all stages of the daily and moult cycles; they were never observed to void any material into the lumen of the hepatopancreas. The differences between the rates of turnover of the contents of the S and B cells have important implications for understanding the dynamics of accumulation and loss of metal pollutants in terrestrial isopods.

Bacteria on the food, in the intestine and on the faeces of the woodlouse Oniscus asellus (Crustacea, Isopoda)

Bacteria on the food, in the intestine and on the faeces of the woodlouse Oniscus asellus (Crustacea, Isopoda)

Species-Specific Differences in the Net Assimilation of Zinc, Cadmium, Lead, Copper and Iron by the Terrestrial Isopods Oniscus asellus and Porcellio scaber

Species-Specific Differences in the Net Assimilation of Zinc, Cadmium, Lead, Copper and Iron by the Terrestrial Isopods Oniscus asellus and Porcellio scaber

Copper and nickel uptake and accumulation, and their effects on redox and electrical potentials of hepatopancreatic cells of Oniscus asellus Linnaeus (Porcellionidae, Isopoda)

Highest tissue Cu concentrations (1728 μg∙g dry weight−1) in whole Oniscus asellus, reared for 7 days on carrot powder containing 50 μg Cu∙g dry weight−1, 10 μg Ni∙g dry weight−1, or a mixture of 50 μg Cu and 10 μg Ni∙g dry weight−1, were observed in isopods on 50 μg Cu∙g dry weight−1, and lowest (917 μg∙g dry weight−1) in those on 10 μg Ni∙g dry weight−1. Highest Ni concentrations (277 and 272 μg∙g dry weight−1) were present in isopods fed on a mixture of 50 μg Cu and 10 μg Ni∙g dry weight−1 and 10 μg Ni∙g dry weight−1, respectively, and lowest (201 μg∙g dry weight−1) in those on 50 μg Cu∙g dry weight−1. Of the total body-tissue Cu, 8–66% was contained in membrane-bound vesicles of hepatopancreatic S-cells, and 73–89% of Ni was present inside the lumen and within S-cells of the hepatopancreas. The presence of Ni in the diet appeared to adversely affect the absorption and hepatopancreatic storage of Cu. Copper slightly enhanced, and nickel drastically reduced, the hepatopancreatic redox (= catalytic activity) and cell-membrane surface potentials. The significance of these findings is discussed.

Responses of the hepatopancreatic ‘B’ cells of a terrestrial isopod,Oniscus asellus, to metals accumulated from a contaminated habitat: A morphometric analysis

The four-lobed hepatopancreas of terrestrial isopods is a highly specialized enzyme secretory, digestive and absorptive region of the midgut. The walls of these blindending tubes are composed of two distinctive epithelial cell types: large, lipid-rich B-cells projecting into the lumen; and small S cells containg (Cu+S)-rich granules. This study investigated the possible stressful effects of accumulated Pb and Zn on the metabolically highly responsive, B-cells. Three major objectives were pursued. First, quantitative electron probe X-ray microanalysis (EPXMA) was employed to determine whether the accumulation of Pb and Zn changes the Fe concentration within individual Fe-granules. Second, simple morphometric techniques were applied to transmission electron micrographs to determine whether competition between essential (Fe) and pollutant (Pb,Zn) metals for binding ligands resulted in an increased granule volume per individual cell. Third, to measure the effect of Pb and Zn accumulation of the amount of stored lipid, in the form of discrete droplets, within the B-cells.

Effects of temperature, and dietary magnesium and nickel levels on magnesium and nickel concentrations during the moult - cycle inOniscus asellus(Porcellionidae, Isopoda, Crustacea)

Mean magnesium concentrations in intermoult Oniscus asellus, caged at 20 degrees C for 10 days, ranged from 1,059.15 +/- 51.9 ppm on diets containing 10 ppm nickel, to 6,827.6 +/- 314.1 ppm on a mixture of 500 ppm magnesium + 10 ppm nickel. Mean nickel concentrations ranged from 89.4 +/- 4.3 ppm on diets containing 500 ppm magnesium, to 314.0 +/- 14.8 ppm on a mixture of 500 ppm magnesium + 10 ppm nickel. At 30 degrees C, magnesium tissue concentrations ranged from 4,149.8 +/- 153.5 ppm on diets with 10 ppm nickel to 12,602.6 +/- 529.3 ppm on 500 ppm magnesium. Nickel concentrations at 30 degrees C varied from 156.8 +/- 6.7 in isopods in the control to 490.5 +/- 23.5 ppm on those on 500 ppm magnesium + 10 ppm nickel. Magnesium in intermoult isopods was mainly stored in other tissues, including the exoskeleton, and nickel in the hepatopancreas. Differences in both magnesium and nickel concentrations between males and females were not significant. Magnesium and nickel concentrations in postmoult isopods, on the average, amounted to 367.6 +/- 16.5 ppm and 18.7 +/- 0.7 ppm, respectively, at 20 degrees C, and 369.9 +/- 16.3 ppm and 30.9 +/- 1.3 ppm, respectively, at 30 degrees C. Differences between males and females, and between various treatments were not significant at P greater than 0.01. It is suggested that both hepatopancreas and other tissues, including the exoskeleton, are used as sinks to get rid of excessive tissue magnesium and nickel during the moult-cycle.

Localization of heavy metals in the hepatopancreas of the terrestrial isopod, Oniscus asellus

Heavy metals have been identified in tissues of a variety of terrestrial isopods exposed to metal polluted sites in Europe. Heavy metals have little effect on some isopods indicating that perhaps the hepatopancreas functions as a detoxifying organ for the isopod by storing the metal. In some lead and copper contaminated rivers tolerant races of the isopod Asellus meridianus were found.Specimens of Oniscus asellus were collected from a cadmium contaminated site adjacent to a marsh in Cold Spring, N. Y. and from an uncontaminated site in New Rochelle, N. Y. Isopods and leaf letter were transported to the lab where some isopods were prepared for scanning electron microscopy (SEM), and others were prepared for atomic absorption spectroscopy. For SEM the hepatopancreatic lobes were fixed in 3,5% glutaraldehyde in 0.1M sodium cacodylate buffer with 0.05% calcium chloride. Specimens were dehydrated in acetone and embedded in Araldite-DDSA. Five micron thick cross sections were deplasticized and gold coated - Sections were viewed and analyzed using an Hitachi S-510 SEM at 25kV with an Ortec 5000 EDX system.

The structure and function of the digestive system of terrestrial isopods

The functional morphology of the digestive system of terrestrial isopods (woodlice) has been investigated. Observations have been made on live juveniles of Oniscus asellus and Porcellio scaber in which some digestive processes can be observed directly through the cuticle. The fine structure of the foregut of juveniles and adults of these two species has been studied by light microscopy and scanning and transmission electron microscopy. The passage of coloured dyes and colloidal gold through the digestive system has also been followed.The digestive system of Oniscus asellus and Porcellio scaber is divided into five regions. The foregut (1), and the anterior chamber (2), papillate region (3) and rectum (4) of the hindgut, are ectodermal in origin and lined with cuticle. The hepatopancreas (5), which opens into the foregut, consists of four blind‐ending tubules which are endodermal in origin and not lined with cuticle. A powerful muscular sphincter is present between the papillate region and the rectum. There is no peritrophic membrane in the lumen of either the hepatopancreas or the hindgut.Fragments of food pass via the oesophagus to the proventriculus of the foregut where they are briefly masticated before passing rapidly into the anterior chamber of the hindgut. During this process, the food is mixed with secretions derived from the hepatopancreas. The anterior chamber possesses a pair of dorsal channels formed from a typhlosole and lateral infoldings of the gut wall. When the hindgut is full of food, contraction of muscles surrounding the gut forces liquids and fine food particles back into the foregut via the typhlosole channels which open at the junction of the anterior chamber and papillate region. This material, which contains fluids derived from the hepatopancreas, and products of digestion, is filtered in the foregut and passed into the lumen of the hepatopancreas where further digestion, and absorption of nutrients, takes place. The hepatopancreas may secrete these fluids back on to the food in the anterior chamber and receive products of digestion via the typhlosole channels several times during a digestive cycle.The lumen of the foregut, hindgut and hepatopancreas often contains a dense population of microorganisms which may be involved in digestion. Residual material in the hindgut passes eventually into the rectum where faecal pellets are compacted before they are voided.The ability of terrestrial isopods to recycle and retain fluids within the digestive system, by the development of the typhlosole channels (which are not present in marine isopods), may have been a major contributory factor in their successful transition from water to land.

The effects of feeding byOniscus asellus (Isopoda) on nutrient cycling in an incubated hardwood forest soil

Oniscus asellus produced changes in the nutrients leached from Oie and Oa horizons of a hardwood forest soil. Soil with isopods lost more K+ (54%) from the Oie horizon and more Ca2+ (25%), Mg2+ (40%), and water-extractable S (23%) from the Oa horizon than soil without isopods. In contrast, soils with isopods lost less Ca2+ (39076) from the Oie horizon and less dissolved C-bonded S (33%) from the Oa horizon than soil without isopods. In addition, the Oia and Oa horizons exhibited different nutrient dynamics. When isopods were present, the Oa horizon leachates accumulated more Na+ K+, Ca2+, Mg2+, NO3− , water-soluble SO42−, and dissolved C-bonded S, and the Oie horizon retained more of these nutrients. The type of leaching solution also had a major effect on nutrients. Leaching with a simulated soil solution resulted in smaller nutrient losses for K+ and Mg2+ in both horizons and for Na+, Ca2+, and NO3− in the Oa horizon than leaching with distilled water.

Phenolic and mineral content of leaves influences decomposition in European forest ecosystems.

Factors influencing decomposition in European forests growing on different soils were studied in stands dominated by the European beechFagus sylvatica L. Phenolic contents of freshly fallen leaves ofF. sylvatica growing on nutrient-poor soils (acid sandy soil) were higher than those of similar leaves on nutrient-rich soils (calcareous mull soil). Analysis of fallen leaves of different ages showed rapid decay of phenolics during the first winter on the ground. After 1 year the phenolic content of leaves ofF. sylvatica growing on nutrient-poor soils was still twice as high as in similar leaves on nutrient-rich soils. Field and laboratory experiments showed that a major decomposer (Oniscus asellus, Isopoda) preferred leaves from trees on nutrient-rich soils. Mineral contents of leaves ofF. sylvatica growing on different soils differed: on rich soils leaves had higher contents of Ca, Mg, Na, and K. These elements are important nutrients for decomposers. The distribution of major decomposers reflects the mineral content of their diet, which in turn reflects soil type. Different rates of leaf turnover and nutrient turnover in different forest ecosystems (even when the same tree species is dominant) are due to the decomposing system, which is influenced by the phenolic and mineral contents of the leaves.

Extracellular application of cobalt: a fast and simple method for delineating invertebrate neurosecretory pathways

The extracellular cobalt backfilling technique was shown to be an excellent method to obtain cobalt backfills of invertebrate neurosecretory cells (NSCs). Aqueous cobalt was placed in an extracellular suction electrode into which a portion of a neurohaemal (NH) region containing the axons and/or terminals of NSCs was drawn. Spontaneously discharging extracellular action potentials were recorded as the cobalt was applied to the NH region, and the greater the electrical activity, the more extensive the cobalt backfilling. The greatest success occurred with 0.5 M cobalt chloride dissolved in physiological saline. No backfills were obtained in the absence of electrical activity. This technique was shown to backfill NSCs terminating in NH regions of the insect, Rhodnius prolixus, the isopod crustacean, Oniscus asellus, and the freshwater pulmonate snail, Helisoma. Combined with a light insensitive silver intensification method, this paper describes a relatively fast and simple method for delineating invertebrate neurosecretory pathways.

Neurosecretory action potentials recorded extracellularly from a neurohemal region associated with the Y-organ in the terrestrial isopod,Oniscus asellus

A long duration (over 30 ms), large amplitude (up to 1000 μV) action potential, was recorded by an extracellular electrode placed near the Y-organ, or molting gland, of the terrestrial isopod,Oniscus asellus. This action potential discharged in a slow tonic fashion (0.20–40.0 spikes per min), and eminated from the lateral nerve plexus (LNP), a neurohemal region believed to control, in part, the activity of the Y-organ. By correlating the rate of electrical activity of the LNP with the molt cycle, it will be possible to assess the role of these neurosecretory cells in regulating the production of ecdysone by the Y-organ.

The occurrence of a rickettsial disease in British woodlice (Crustacea, Isopoda, Oniscidea) populations

During a structural study of the gut and tegumental glands of the woodlouse Porcellio scaber Latreille, numerous darkly staining spindle-shaped bodies were found in certain tissues. These proved to be elementary bodies of Rickettsiella grylli (Rickettsiales, Rickettsiaceae). Details of its structure and distribution within the host tissues are given, including the rosette-type tegumental glands and a type of tissue not seen in woodlice before, the vesicular bodies (also found in healthy specimens). This is the first time that this pathogenic organism has been recorded in P. scaber and the first record for R. grylli from the British Isles. The rickettsial disease may also be present in British populations of the woodlice Oniscus asellus Linnaeus and Armadillidium vulgare (Latrielle).

The effects of feeding by Oniscus asellus on leaf litter sulfur constituents

Feeding by the isopod, Oniscus asellus, produced changes in the sulfur constituents of leaf litter substrates (Acer negundo, A. saccharum, Fagus grandifolia, Picea rubens, and Tsuga canadensis). Isopod consumption of leaf litter generally accelerated the mineralization of carbon-bonded S and increased the formation of ester sulfate in all substrates. After the isopod egestion of A. negundo leaves, fecal decomposition over 6 weeks increased total S concentration from 68 to 120 μmol S/g due to the catabolism of organic carbon. During the same period sulfate decreased from 34 to 20 μmol S/g and carbon-bonded S increased from 34 to 100 μmol S/g. Thus the total S pool in aged feces became enriched with organic S (83% of total S). Macroinvertebrate consumption accelerated the transformation of S constituents and the carbon-bonded S concentration approached that of the Oa organic horizon of a northern hardwood forest.