Paracellular pathway in the shell epithelium of Anodonta cygnea

Ultrastructural study of cell-cell connections in the outer mantle epithelium (OME) on high-pressure-frozen specimens revealed zonula adherens, septate junctions and gap junctions in Anodonta cygnea. In order to evaluate the permeability of the paracellular pathway, the OME was incubated under gradients of lanthanum and calcium. After lanthanum incubation (4 mM) from the basal side, the septate junctions were penetrated completely by this tracer. When applied from the apical side, lanthanum deposits were located similarly over the entire length of the septate junctions up to the first dilatations of the intercellular space. Calcium deposits were also present in paracellular areas only when OME had been incubated simultaneously with calcium (6 mM) and lanthanum (4 mM) gradients. Lanthanum and calcium deposits were detected with ESI (Electron Spectroscopic Imaging) and identified with EELS (Electron Energy Loss Spectroscopy). On the other hand, electrophysiological observations showed a 48% reduction of conductance when the OME was bathed on both sides with solutions containing lanthanum (4 mM) and calcium (6 mM), compared to bathing with lanthanum-free solution (control). The conductance reduction was 52% when calcium was removed from the control solution. Supported by morphological and physiological evidence, it appears that, under in vivo conditions, calcium ions may diffuse paracellularly from the haemolymph towards the extrapallial fluid and vice-versa across the septate junctions in the OME of A. cygnea. Permeability of the septate junctions depended proportionally on the calcium concentration in fluids.     

Anal uptake of water in terrestrial pulmonate snails

Summary The uptake of water was examined in 35 central European terrestrial pulmonate snail species from 15 families (Table 1) by giving the inactive, withdrawn animals dyed water and observing its bulk flow microscopically.During emergence, 32 of the species studied normally take up water through the pneumostome. A rectal pump (Figs. 1 and 2) rapidly conveys this water through the anus into the gut and stomach.In 7 species, anal water-uptake during emergence was quantified and found to be equivalent to 20–40% of the total body water of the inactive snails before water uptake (Table 2).After emergence, the rectal pump allows re-uptake of urine from the ureter or the lung cativity into the alimentary tract.The anal mechanism permits rapid uptake of large quantities of water into an extrasomal compartment. This helps terrestrial pulmonate snails to exploit short wet spells and presumably helps to stabilize blood concentration during activity under dry conditions.     

Field observation of predation on paper wasp nests by introduced terrestrial slugs

Nest predation is an important factor in the colony mortality of paper wasps. Although a variety of animals are known to prey on paper wasp nests, colony failure of unknown cause often occurs in the field, and the existence of still-unknown predators is possible. Here, I report predation on nests of paper wasps, Polistes chinensis antennalis, by introduced terrestrial slugs, Lehmannia valentiana. The slugs were found on the wasps’ nests despite the presence of the owners on the nests and ate eggs, larvae, and presumably cell walls of the nests. This is the first report of predation on paper wasp nests by slugs.     

Cold tolerance and freeze-induced glucose accumulation in three terrestrial slugs

Cold tolerance and metabolic responses to freezing of three slug species common in Scandinavia (Arion ater, Arion rufus and Arion lusitanicus) are reported. Autumn collected slugs were cold acclimated in the laboratory and subjected to freezing conditions simulating likely winter temperatures in their habitat. Slugs spontaneously froze at about − 4 °C when cooled under dry conditions, but freezing of body fluids was readily induced at − 1 °C when in contact with external ice crystals. All three species survived freezing for 2 days at − 1 °C, and some A. rufus and A. lusitanicus also survived freezing at − 2 °C. ¹H NMR spectroscopy revealed that freezing of body fluids resulted in accumulation of lactate, succinate and glucose. Accumulation of lactate and succinate indicates that ATP production occurred via fermentative pathways, which is likely a result of oxygen depletion in frozen tissues. Glucose increased from about 6 to 22 μg/mg dry tissue upon freezing in A. rufus, but less so in A. ater and A. lusitanicus. Glucose may thus act as a cryoprotectant in these slugs, although the concentrations are not as high as reported for other freeze tolerant invertebrates.     

Cold tolerance and freeze-induced glucose accumulation in three terrestrial slugs

Cold tolerance and metabolic responses to freezing of three slug species common in Scandinavia (Arion ater, Arion rufus and Arion lusitanicus) are reported. Autumn collected slugs were cold acclimated in the laboratory and subjected to freezing conditions simulating likely winter temperatures in their habitat. Slugs spontaneously froze at about -4 °C when cooled under dry conditions, but freezing of body fluids was readily induced at -1 °C when in contact with external ice crystals. All three species survived freezing for 2 days at -1 °C, and some A. rufus and A. lusitanicus also survived freezing at -2 °C. (1)H NMR spectroscopy revealed that freezing of body fluids resulted in accumulation of lactate, succinate and glucose. Accumulation of lactate and succinate indicates that ATP production occurred via fermentative pathways, which is likely a result of oxygen depletion in frozen tissues. Glucose increased from about 6 to 22 μg/mg dry tissue upon freezing in A. rufus, but less so in A. ater and A. lusitanicus. Glucose may thus act as a cryoprotectant in these slugs, although the concentrations are not as high as reported for other freeze tolerant invertebrates.     

Consequences of competition on the reproduction and mortality of three species of terrestrial slugs

The interaction of three species of terrestrial slugs was studied in six field cages containing monocultures and 2-way combinations. A. columbianus and A. ater were non-aggressive species and L. maximus was highly aggressive during the summer. All three species were similar in body design and resource utilization. Reproduction (egg size, eggs/batch, number of batches, wet-weight productivity) and mortality were monitored through the 1977 season. L. maximus drastically reduced reproductive success of the non-aggressive slugs and increased their mortality. There were also significant interactions between the non-aggressive species. Compared to other invertebrates, the life history characteristics of A. columbianus are strongly K-selected and probably evolved through intraspecific exploitative competition in predictable, stable forest habitats. A. ater is best classified as a refuging r-selected species adapted to less predictable, unstable field environments. L. maximus appears to be α-selected and its overall design is suited to density-dependent regulation in fields.     

Beta-adrenergic activation of solute coupled water uptake by toad skin epithelium results in near-isosmotic transport

Transepithelial potential (V(T)), conductance (G(T)), and water flow (J(V)) were measured simultaneously with good time resolution (min) in isolated toad (Bufo bufo) skin epithelium with Ringer on both sides. Inside application of 5 microM isoproterenol resulted in the fast increase in G(T) from 1.2+/-0.3 to 2.4+/-0.4 mS x cm(-2) and slower increases in equivalent short circuit current, I(SC)(Eqv) = -G(T) x V(T), from 12.7+/-3.2 to 33.1+/-6.8 microA cm(-2), and J(V) from 0.72+/-0.17 to 3.01+/-0.49 nL cm(-2) s(-1). Amiloride in the outside solution abolished I(SC)(Eqv) (-1.6+/-0.1 microA cm(-2)) while J(V) decreased to 0.50+/-0.15 nL cm(-2) x s(-1), which is significantly different from zero. Isoproterenol decreased the osmotic concentration of the transported fluid, C(osm) approximately 2 x I(SC)(Eqv)/J(V), from 351+/-72 to 227+/-28 mOsm (Ringer's solution: 252.8 mOsm). J(V) depicted a saturating function of [Na+]out in agreement with Na+ self-inhibition of ENaC. Ouabain on the inside decreased I(SC)(Eqv) from 60+/-10 to 6.1+/-1.7 microA cm(-2), and J(V) from 3.34+/-0.47 to 1.40+/-0.24 nL cm(-2) x s(-1). Short-circuited preparations exhibited a linear relationship between short-circuit current and J(V) with a [Na+] of the transported fluid of 130+/-24 mM ([Na+]Ringer's solution = 117.4 mM). Addition of bumetanide to the inside solution reduced J(V). Water was transported uphill and J(V) reversed at an excess outside osmotic concentration, deltaC(S,rev) = 28.9+/-3.9 mOsm, amiloride decreased deltaC(S,rev) to 7.5+/-1.5 mOsm. It is concluded that water uptake is accomplished by osmotic coupling in the lateral intercellular space (lis), and hypothesized that a small fraction of the Na+ flux pumped into lis is recirculated via basolateral NKCC transporters.     

Epidermal secretions of terrestrial flatworms and slugs: Lehmannia valentiana mucus contains matrilin-like proteins

We describe the epidermal mucus of two types of terrestrial invertebrates: free-living flatworms (Tricladida: Terricola), and the slug Lehmannia valentiana (Gastropoda: Pulmonata). Both exhibited similar dry shear strengths (1.4-1.7 MPa). In denaturing gel electrophoresis, the protein fraction of flatworm mucus migrated mainly as a broad band (200-300 kDa). Slug mucus had a higher protein content than flatworm mucus but it contained more carbohydrate than protein, mainly as large heparan sulfate-like glycosaminoglycans. Proteins and glycosaminoglycans were both essential for the mechanical integrity of the slug hydrogel. The protein fraction of slug mucus contained approximately 12 larger proteins (30-300 kDa) and approximately 6 smaller ones (10-28 kDa). Complete cDNA clones were obtained for the slug mucus 40 kDa protein (Sm40; Genbank accession EF634345) and 85 kDa protein (Sm85; Genbank accession EF634346). Both proteins contain EGF-like repeats and von Willebrand A-domains, and therefore resemble vertebrate matrilins. Many of the larger slug mucus proteins appear to contain A-domains, and these may play a role in the unusual rheological properties of gastropod mucus.     

陆地生态系统植物的氮源及氮素吸收

氮是植物生长发育所必需的营养元素,也是其主要的限制因子之一.陆地生态系统植物所需氮的来源及植物对氮素的吸收利用均受控于其种类和生长环境.环境条件的改变,一方面可能改变植物生长区原有氮的形态、浓度、赋存方式等,从而改变氮对植物的供给状况;另一方面可能引起植物生长区土壤质量、水分利用状况、光照等的改变,从而产生耦合现象,直接影响植物的生理生态特性,使植物对氮素的吸收利用发生改变,导致植物生长区的种群类型及物种多样性发生改变,并直接影响到生态系统的功能及演替.本文主要对陆地生态系统中高等植物生长发育所需氮素的来源及植物对氮素吸收利用过程中的影响因素进行了综述和讨论,并结合国内外在该领域的研究现状对其研究前景进行了展望.     

Diversity and distribution of nematodes associated with terrestrial slugs in the Western Cape Province of South Africa

A survey of nematodes associated with native and introduced species of terrestrial slugs was conducted in the Western Cape Province of South Africa, in order to gather new data regarding diversity and distribution. A total of 521 terrestrial slugs were collected from 35 localities throughout the Western Cape. All slugs were dissected and examined for the presence of internal nematodes. Extracted nematodes were identified using a combination of molecular (18S rRNA gene sequencing) and morphological techniques. Nematodes were found parasitizing slugs at 14 of the 35 sites examined, amounting to 40% of sample sites. Of all slugs, 6% were infected with nematodes. A total of seven species of nematode were identified in the province, including Agfa flexilis, Angiostoma sp., Phasmarhabditis sp. SA1, Phasmarhabditis sp. SA2, Caenorhabditis elegans, Panagrolaimus sp. and Rhabditis sp. Of these species, four were thought to be parasitic to slugs (A. flexilis, Angiostoma sp., Phasmarhabditis sp. SA1 and Phasmarhabditis sp. SA2), as opposed to forming necromenic or phoretic associations. Three new species of slug-parasitic nematode were identified during this study (Angiostoma sp., Phasmarhabditis sp. SA1 and Phasmarhabditis sp. SA2).     

The use of electrophoresis in the separation of two closely related species of terrestrial slugs

The pattern of variation of non-specific esterases, revealed by the use of disc electrophoresis, was used in an investigation of the specific difference between Limax flavus and L. pseudoflavus. The isozyme patterns were used to differentiate between the two taxa both qualitatively and quantitatively. The results were in agreement with the results from studies of the variation in the morphology of the distal portions of the genitalia and of external body colouration and patterning. The biochemical methods allowed a rapid estimation of the difference between the two taxa and were more precise than the use of colour variation.     

Consequences of competition on the time budgets,growth and distributions of three species of terrestrial slugs

Summary The behavioural time budgets of two non-aggressive slugs and one aggreessive species were evaluated in monocultures or in 2-way combinations in field cages. The seasonal time budgets ofL. maximus, A. ater andA. columbianus in monoculture were remarkably similar despite their strong differences in physiological resource allocation. Similarity in physical design and resource utilization appeared to be more important determinants of behaviour. The time budgets showed distinct seasonal patterns associated with underlying physiological demands for reserve accumulation, sperm acquisition and oviposition.A. ater andL. maximus displayed a definite dispersal phase associated with femalephase maturation. In combination,A. ater andA. columbianus had no detectable effect on one another’s time budgets.L. maximus disrupted nearly every category of behaviour in these non-aggressive species, but its own time budget was not significantly different in the monoculture or in the two combinations, except for minor effects on resting and sexual behaviour.L. maximus appeared to be adapted to maximize behavioural disturbance of interspecific competitors while minimizing intraspecific effects.     

Fern and bryophyte endozoochory by slugs

Endozoochory plays a prominent role for the dispersal of seed plants, and dispersal vectors are well known. However, for taxa such as ferns and bryophytes, endozoochory has only been suggested anecdotally but never tested in controlled experiments. We fed fertile leaflets of three ferns and capsules of four bryophyte species to three slug species. We found that, overall, spores germinated from slug feces in 57.3 % of all 89 fern and in 51.3 % of all 117 bryophyte samples, showing that the spores survived gut passage of slugs. Moreover, the number of samples within which spores successfully germinated did not differ among plant species but varied strongly among slug species. This opens new ecological perspectives suggesting that fern and bryophyte endozoochory by gastropods is a so-far-overlooked mode of dispersal, which might increase local population sizes of these taxa by spore deposition on suitable substrates.     

Organic cation uptake by a cultured renal epithelium

Several organic cations are actively transported by proximal renal tubules by mediated processes across both the apical and basolateral cell membranes. In order to evaluate this transport system in a cultured renal epithelium, uptake of 3H-tetraethylammonium (TEA) across the apical membrane was measured in LLCPK1 cells, a cell line with several characteristics of proximal tubules. 3H-TEA progressively entered these cells and reached a near-steady state by 30 min. Three-minute uptake was saturable with an apparent Vmax of 1,669 +/- 129 fmoles/micrograms DNA and apparent Km of 34.0 +/- 3.4 microM. 3H-TEA uptake was inhibited by an excess of nonradioactive TEA, other organic cations, sodium azide, and hypothermia. An alkaline external pH was associated with greater 3H-TEA uptake than an acid pH. However, efflux of 3H-TEA from cells was not appreciably affected by changes in external pH. Preincubation of cells in acid or alkaline media did not affect uptake. Alteration of cell pH by ammonium chloride addition or removal had little effect on 3H-TEA uptake. Finally, uptake of 3H-TEA was not accelerated by preloading cells with an excess of nonradioactive TEA. These results indicate that intact LLCPK1 cells possess a mechanism(s) in their apical membranes for the mediated transport of a prototypic organic cation. The mechanism(s) involved in this transport is uncertain. However, neither organic cation/proton nor organic cation/organic cation exchange appears to be the predominant process.