The influence of nutritional status on the feeding behaviour of the field slug, Deroceras reticulatum (Müller)

The field slug, Deroceras reticulatum, a common pest of agricultural and horticultural crops, is a generalist herbivore with distinct preferences for particular food items. However, these preferences are not fixed, but are influenced by the recent dietary history of the slugs. In particular, slugs tend to select novel food items ('neophilia'). We investigated the basis of such influences, using artificial diets in which protein and carbohydrate composition could be controlled and non-nutritional ('secondary') chemicals added as flavours. The slugs showed no general inclination for neophilia based on taste alone. There was a possible learned association between protein content and taste, but this was weakly expressed. However, the slugs selected food items, when given a choice, containing nutrients that were deficient in earlier diets, even though all the food items contained the same familiar secondary taste chemicals. Injections of missing nutrients into the haemocoel of slugs inhibited such changes in food preference, indicating that slugs' feeding preferences are influenced directly by their internal nutritional status. We suggest that neophilia in D. reticulatum is a physiological response to a nutritional imbalance arising from a suboptimal diet. Copyright 2000 The Association for the Study of Animal Behaviour.     

Transgenic Arabidopsis leaf tissue expressing a modified oryzacystatin shows resistance to the field slug Deroceras reticulatum (Müller)

Transgenic Arabidopsis thaliana has been developed which expresses the oryzacystatin mutant OCI86, which is an inhibitor of the major proteinase present in the digestive gland of the slug, Deroceras reticulatum. When fed on leaf tissue from plants expressing this inhibitor the growth of juvenile slugs was significantly reduced by 31% compared with those feeding on control leaf tissue. Furthermore, while surviving slugs did not individually consume less when feeding on leaf tissue expressing OCI86, the total amount of leaf tissue eaten was 50% less, due to reduced survival of slugs. The synthetic cysteine proteinase inhibitors E64 and leupeptin also significantly reduced slug weight gain (by at least 40%) and digestive gland cysteine proteinase activity when administered in an artificial diet, indicating that their antimetabolic effects are due to direct inhibition of gut proteolytic activity. These results suggest that transgenic crop plants expressing phytocystatins could be used to suppress the growth rates of slug populations in the field.     

Palatability of weeds from different European origins to the slugs Deroceras reticulatum Müller and Arion lusitanicus Mabille

As part of a study on the significance of seed provenances in schemes to enhance biodiversity in agricultural habitats, juvenile plants of Cichorium intybus, Daucus carota, Leucanthemum vulgare and Silene alba of different European origins were exposed to grazing by two slug species, Deroceras reticulatum and Arion lusitanicus. Living plants were offered in trays, either in a glasshouse (Deroceras) or outdoors (Arion). The amount of herbivory was origin-dependent, with higher losses for all four species from German and Hungarian provenances compared with English and Swiss plants. The main trend was similar for both slug species except in the case of Daucus, and there was a significant ‘origin × plant species’ interaction. We found strong correlations between provenance-specific herbivory and certain climatic characteristics of the corresponding regions, i.e. winter minimum temperatures, and dryness in spring and late summer, which are crucial for the development of slugs. The results can be interpreted in terms of a SW-NE European climatic gradient and may be a consequence of differences in the need for plant defences against herbivory by slugs. Additionally, the data on palatability were compared with susceptibility towards two parasites which occurred in a field experiment, a leaf miner on Leucanthemum vulgare and a rust fungus on Silene alba. While specific leaf mining frequencies on Leucanthemum contrasted with the palatability of the different provenances to slugs, the rust infection on Silene was low on local and German plants, and higher on the more distant provenances from England and Hungary.     

Reproduction, growth and circadian activity of the snail Bradybaena fruticum (O. F. Müller, 1774) (Gastropoda: Pulmonata: Bradybaenidae) in the laboratory

Selected life cycle parameters of the snail Bradybaena fruticum were studied in the laboratory. The initial material for the laboratory culture was taken from a population in South Western Poland; the snails were kept in Petri dishes and plastic containers. The temperature, humidity and lighting conditions were maintained at a constant level (day 18°C, night 12°C, rh 80%, light:dark 12:12). Circadian activity observations were conducted outside the climatic chamber. Eggs — calcified, slightly oval, of mean dimensions 2.67x2.56 mm — were laid singly or in batches of 6–62, as a result of both biparental and uniparental reproduction. Incubation took 27–76 days and hatching was asynchronous. Hatching success was lower among eggs produced by single parents compared to eggs produced by two parents (c.a. 56 and c.a. 88%, respectively). Growth included fast (2.25 to 5 whorls) and slow (1.9–2.25 and >5 whorls) phases as well as lip formation, and took 261 to 420 days. The first eggs/batches were laid c.a. one year later, and for uniparentally reproducing snails the period was even longer. The growth of snails kept singly was faster than in those kept in groups. Juvenile snails were much more active than adults in the spring, summer and autumn but the adults were more mobile in the winter. In all seasons, juveniles were more active at night than adults.     

Studies on the ovotestis of the slug Agriolimax reticulatus (Müller)

Summary The follicle cells, nurse cells and germinal epithelia, which are closely associated with the oocyte of Agriolimax reticulatus (Müller) during its development in the ovotestis, have been studied using light and electron microscopy. The various secretory, digestive and phagocytic activities of these cells have also been investigated using electron cytochemical tests for oxidisable polysaccharide, acid phosphatase and electron-opaque tracer molecules. The oocyte lies initially between the germinal epithelia and a layer of nurse cells but, as oocyte vitellogenesis proceeds, it becomes encapsulated by a layer of follicle cells. Both the follicle and the nurse cells are active in secretion and digestion and contain Golgi apparatus, granular endoplasmic reticulum and acid phosphatase-rich digestive vacuoles. The significance of these activities is discussed in relation to oocyte vitellogenesis, secondary envelope formation and the digestion and recycling of cellular material.     

Studies on the ovotestis of the slug Agriolimax reticulatus (Müller)

Summary The ovarian oocytes of Agriolimax reticulatus (Müller) have been studied by light and electron microscopy and electron cytochemistry. The development of the oocyte in the ovotestis may be divided into three stages.During Stage I the oocyte cytoplasm contains mainly ribosomes and also strands of endoplasmic reticulum, scattered mitochondria and Golgi systems. The nucleus contains both a paranucleolus and an eunucleolus. By Stage II the oocyte has enlarged, especially in a plane parallel to the basement membrane. In addition to the above mentioned organelles, the cytoplasm contains lipid, glycogen and early yolk platelets. During Stage III, the oocyte continues to enlarge, but mainly in a plane perpendicular to the basement membrane. A considerable degree of cytoplasmic differentiation has also taken place. The plasma membrane of the oocyte has become specialized with the appearance of a polysaccharide-rich glycocalyx, microvilli and pinocytotic tubules. Elsewhere, much of the background cytoplasm, containing Golgi-derived, polysaccharide and acid phosphatase-rich multivesiculate bodies, lipid and glycogen, is sequestered by smooth membranes and ultimately fuses with the growing yolk platelets. The nucleus contains an amphinucleolus, characteristic of many gastropods.The findings of this study are discussed in relation to results from other studies on oogenesis.     

The mitochondrial genome of the land snail Camaena cicatricosa (Müller, 1774) (Stylommatophora,Camaenidae): the first complete sequence in the family Camaenidae

The complete mitochondrial (mt) genome of the snail Camaena cicatricosa (Müller, 1774) has been sequenced and annotated in this study. The entire circular genome is 13,843 bp in size and represents the first camaenid mt genome, with content of 31.9%A, 37.9%T, 13.5%C and 16.7%G. Gene content, codon usage and base organization show similarity to a great extent to the sequenced mt genome from Stylommatophora, whereas, gene order is different from them, especially the positions of tRNA^Cys, tRNA^Phe, COII, tRNA^Asp, tRNA^Gly, tRNA^His and tRNA^Trp. All protein coding genes use standard initiation codons ATN except for COII with GTG as start signal. Conventional stop codons TAA and TAG have been assigned to all protein coding genes. All tRNA genes possess the typical clover leaf structure, but the TψC arm of tRNA^Asp and dihydrouridine arm of tRNA^Ser(AGN) only form a simple loop. Shorter intergenic spacers have been found in this mt genome. Phylogenetic study based on protein coding genes shows close relationship of Camaenidae and Bradybaenidae. The presented phylogeny is consistent with the monophyly of Stylommatophora.     

Life history of Lineus viridis (Müller, 1774) (Heteronemertea, Nemertea)

Lineus viridis is a common nemertean species of North-Atlantic intertidal sand flats. Its mating behaviour is peculiar insofar as this species is reported to be polyandric. However, detailed information on this topic is lacking. In order to get more data on the reproduction, oogenesis and life history of this species, a population in the Wadden Sea on the Isle of Sylt (North Sea) was studied between 2005 and 2011. We conducted regular surveys, during which we sampled, measured and recorded the sex status of 25–100 individuals at each sampling event; at least three individuals were fixed for histological studies at each sampling date. In addition, animals were kept in the laboratory for 3?years to complement field data on sexual identity. Lineus viridis was found to reproduce annually in several successive year; the females are significantly larger than the males. Oogenesis starts in spring, shortly after the preceding reproductive period, and continues until the end of December. Spermiogenesis starts in late autumn and also ends late in December. During mating, several males are generally found crawling on a single female, which forms a cocoon that encloses both the female and the associated males. Fertilization is internal. While females discharge all of their eggs during a single mating event and lose more than 40% of their wet weight, males only empty a few of their gonads, and are thus able to fertilize more than one female. Our study clearly shows that Lineus viridis is a perennial, iteroparous species with a pronounced sexual size dimorphism. During this long-term study, no evidence for sequential hermaphroditism has been found. The observed polyandric mating system in this species raises further questions regarding mate and sperm competition that deserve additional research.     

Micro-structure and chemical composition of vateritic deformities occurring in the bivalve Corbicula fluminea (Müller, 1774)

Vateritic deformities occurring in the invasive heterodont bivalve Corbicula fluminea from several locations in the UK were characterised in detail for the first time using scanning electron microscopy, X-ray diffraction and different geochemical techniques (electron microprobe, ICP-AES, and mass spectrometry). Large volumes of vaterite are produced abnormally in the animals' shells in the form of yellow-green bulges. These are distinguished from the aragonitic parts of the shell by their characteristic micro-structures, content of organic material, trace elemental composition and carbon stable isotope signatures. The most commonly observed micro-structures include columnar vaterite, lamellar vaterite and different irregular structures occurring in all parts of the shell. There are indications that organic material is present largely as intracrystalline impurities or nano-scale phases and not as envelopes around microstructural units. These micro-structures are novel, nothing equivalent having yet been described for other vateritic systems. Euhedral vaterite crystals also occur occasionally. The vaterite has generally higher Mg/Ca and lower Na/Ca, K/Ca than the aragonite. In addition, δ13C is also always lower. Microstructural characteristics would suggest loss of biological control probably due to physiological stress(es) inducing the switch to vaterite production. The vaterite might be stabilised by its higher content of organic material and magnesium.     

Morphological study of muscular tissue collagen of wild and reared Cornu aspersum (Müller, 1774)

Muscular tissue collagen fibrils’ diameter and period of reared and wild snails (Cornu aspersum) were measured in order to investigate the role of nutrition on the collagen. Wild adult individuals were collected from Crete (Greece) and compared with adult individual snails reared under laboratory conditions fed a formulated diet. Transmission electron microscope and image analysis algorithms were used in the study. Statistically significant differences between the diameters of the collagen fibrils in the reared and the wild snails were found, and the D-period of the fibrils differed.     

The cytology,histochemistry, and ultrastructure of the cell types found in the digestive gland of the slug,Agriolimax reticulatus (Müller)

Summary Four cell types have been identified in the digestive glands from light and electron microscope studies. The possible functions of each cell type are discussed.Thin cells are undifferentiated. Calcium cells contain spherules of calcium salts which have a characteristic ultrastructure. Different protein granules are found apically. Digestive cells are present as two distinct forms. One form is believed to be absorbing food material and digesting it intracellularly, and the other form is a secreting cell. Both forms contain green and yellow granules and histochemistry shows these granules to be distinct. Protein granules also occur apically.Excretory cells are distinguished by having a large central vacuole containing excretory granules. Histochemistry shows these granules, like the yellow granules of digestive cells, to be composed mainly of lipofuscin.It is suggested that digestive cells form excretory cells.     

Quantification of sediment reworking by the Asiatic clam Corbicula fluminea Müller, 1774

Active organisms modify the substratum in which they dwell. This process, called “bioturbation”, affects the way that biogeochemical fluxes are mediated at the substratum–water interface. In the frame of this work, the bioturbation potential of the Asiatic clam Corbicula fluminea was characterized and quantified. We measured the displacement of fluorescent particles by C. fluminea burying in a size-based experimental design in order to explore the effects of body-size on sediment reworking. Our results stress that C. fluminea belongs to the functional group of biodiffusors, and that C. fluminea can be considered as an intermediate sediment reworker. We suggest that bioturbation was mainly induced by the pedal-feeding activity of the clams. Results also showed that, though large clams induced displacement of particles deeper into the sediment, small clams showed the highest net sediment reworking activity. This result was in contrast to the initial hypothesis of biovolume as the main driver for particle displacement by bioturbating organisms. Life-history traits and specific features of pedal-feeding could explain the observed pattern.     

Some characteristics of genetic variants of Tubifex tubifex (Müller, 1774) (Oligochaeta: Tubificidae) in laboratory cultures

Genetic variants of the oligochaete Tubifex tubifex were identified with enzyme electrophoresis and subsequently reared in laboratory cultures. Three types are abundant in field populations. Individuals that show homozygotic bands of glucosephosphate-isomerase (GPI) 22 together with isocitrate-dehydrogenase (IDH) 35 were labeled Type A. Type B is characterized by GPI 23 together with IDH 11 and Type C is characterized by GPI 11 with either IDH 34 or IDH 33. Initial results on freshweights of adults and cocoon production revealed differences between the two main types, A and B. In the same period, Type B reached higher weights and produced five times as many cocoons as Type A, whereas number of eggs per cocoon were not different between these Types. Type B also had the lowest mortality in 16-week experiments with changing temperatures.     

Mannan-degrading enzymes purified from the crop of the brown garden snail Helix aspersa Müller (Gastropoda Pulmonata)

Two mannan-degrading enzymes were purified from the crop of the terrestrial snail Helix aspersa Müller. The crude extracts were taken from dormant (for 4 months) snails. The enzymes were a betaD-mannanase of 37.4 +/- 0.3 kDa (EC 3.2.1.78) and a betaD-mannosidase of 77.8 +/- 1.9 kDa (EC 3.2.1.25). Both enzymes degraded insoluble mannan, releasing either mannose only (beta-mannosidase) or oligosaccharides, possibly mannotriose and mannopentaose (beta-mannanase). The beta-mannanase had a typical endo-activity pattern, while the beta-mannosidase was an exoenzyme. The incubation of both enzymes with mannan increased the catalysis by 83%. The best synergy was found with 75% mannosidase combined with 25% mannanase. The beta-mannanase also hydrolysed beta-linked heteromannans and its affinity for different galactomannans was studied. The Km values, varying from 2.89 +/- 0.47 mg x ml(-1) to 0.26 +/- 0.01 mg x ml(-1), revealed the inhibitory effect of the alphaD-galactosyl residues released. The beta-mannosidase was acidic (optimum pH = 3.3) and heat-sensitive (50% residual activity at 42 degrees C after 5 min of pre-incubation), while the beta-mannanase remained stable until 48.5 degrees C (50% residual activity) and over a pH range of 4.3-7.5. The properties of these mannanolytic enzymes are discussed in this paper compared with those purified in other gastropods and in a bacterium, Enterococcus casseliflavus, a quite similar strain previously isolated from this snail intestine. The occurrence of thermostable enzymes in H. aspersa digestive tract could be a zootechnic parameter of great importance for snail farming. J. Exp. Zool. 290:125-135, 2001.     

Life cycle and identification of an eyefluke from Israel transmitted by Melanoides tuberculata (Müller, 1774)

A philophthalmid species from Israel using the freshwater snail Melanoides tuberculata as intermediate host was studied. The biological and morphological characteristics of all developmental stages of the life cycle of this philophthalmid were described, and compared to those of Philophthalmus lucipetus Rudolphi, 1819 from Israel, Philophthalmus gralli Mathis and Leger, 1910 from Jordan, Philophthalmus palpebrarum Looss, 1899, Philophthalmus nocturnus Looss, 1907, Cercaria distomatosa Looss 1896 from Egypt, and Philophthalmus lucknowensis Baugh, 1962 from India. The possible identity with 1 of these species is discussed. On the basis of comparative analysis of the data for all parasite stages in the life cycle, geographical distribution, snail hosts, and snail host specificity, we propose to designate the Israeli Melanoides tuberculata-transmitted eye fluke to Philophthalmus distomatosa n. comb. (Looss, 1896), (Digenea: Philophthalmidae).     

Habitat preference of freshwater snails in relation to environmental factors and the presence of the competitor snail Melanoides tuberculatus (Müller, 1774)

Our objective is to evaluate the habitat preference of freshwater snails in relation to environmental factors and the presence of the competitor snail Melanoides tuberculatus. In the first phase, snails was collected at 12 sites. This sampling sites presented a degree of organic input. In the second phase 33 sampling sites were chosen, covering a variety of lotic and lentic environments. The snail species found at Guapimirim, state of Rio de Janeiro, displayed a marked habitat preference, specially in relation to the physical characteristics of each environment. Other limiting factors for snail distribution at the studied lotic environments were the water current velocity and the amount of organic matter, mainly to Physa marmorata, M. tuberculatus, and Biomphalaria tenagophila. The absence of interactions between M. tuberculatus and another snails could be associated to the distinct spatial distribution of those species and the instability of habitats. This later factor may favor the coexistence of M. tuberculatus with B. glabrata by reduction of population density. In areas of schistosomiasis transmission some habitat modification may add to the instability of the environment, which would make room for the coexistence of M. tuberculatus and Biomphalaria spp. In this way, some of the usual measures for the control of snail hosts would prevent the extinction of populations of Biomphalaria spp. by M. tuberculatus in particular habitats.     

A field test of a sediment bioassay with the oligochaete worm Tubifex tubifex (Müller, 1774)

A sediment toxicity test using reproduction in the tubificid oligochaete Tubifex tubifex was tested in 11 geographic locations in the Laurentian Great Lakes where sediments have previously been documented as being contaminated. Samples were taken from both potentially contaminated and clean sites in each of the 11 areas. Using test endpoints such as survival and growth, results from 72 samples were classified using cluster and ordination techniques. Six response groups were identified and four groups of toxic sites determined. Toxic effects ranged from mortality of adult worms to reduced reproduction. Using correlation and discriminant analysis there was good evidence that high concentrations of metals such as copper and lead were responsible for the observed effects at some sites.     

Allozyme variation in the camaenid tree snails Amphidromus atricallosus (Gould, 1843) and A. inversus (Müller, 1774)

We examined allozyme variation in two camaenid tree snails, Amphidromus atricallosus and A. inversus, across two principal regions of Thailand and from Singapore, plus for A. inversus, one site in peninsular Malaysia. Using horizontal starch gel electrophoresis, 13 allozyme loci (11 polymorphic) were screened for A. atricallosus and 18 (5 polymorphic) for A. inversus. Heterozygosity was higher in A. atricallosus (Hexp=0.018-0.201, mean=0.085) than in A. inversus (Hexp=0-0.023, mean= 0.002). Genetic heterogeneity among samples was higher in A. inversus (Fst=0.965) than in A. atricallosus (Fst=0.781). Within A. atricallosus, populations were more differentiated in southern Thailand (Fst=0.551) than in eastern Thailand (Fst=0.144). The high Fst and low Hexp in populations of A. inversus suggest that this species is likely to have experienced a series of strong bottlenecks, perhaps occurring chiefly on offshore continental-shelf islands. The low Fst values of A. atricallosus in eastern Thailand suggest frequent gene flows among populations in this region. The southern and eastern samples of A. atricallosus exhibited fixed allele differences at four loci and great genetic distance (Nei's D=0.485-0.946), suggesting that these two samples may actually represent, or else be evolving into, separate species.     

Invasion by the Introduced Aquatic Snail Melanoides tuberculata (Müller, 1774) (Gastropoda: Prosobranchia: Thiaridae) of the Rio Doce State Park,Minas Gerais,Brazil

During quantitative samples of invertebrate fauna in two lakes in the Rio Doce State Park (Marliéria, MG) I found some individuals of the introduced aquatic snail Melanoides tuberculata. It was most abundant in areas with high human activity, where the original vegetation was removed from the shallow areas near the margin. Population structure inferred by size-class data suggests that the most impacted area was invaded first and that these snails maintain a viable population in Dom Helvécio lake. Potential spread of the snail in this lake system is tentatively related to the characteristics of the bank vegetation and I presume that the not yet invaded Carioca lake has better conditions for an exponential growth of this species.