Habitat preferences of Ukrainian brook lamprey Eudontomyzon mariae ammocoetes in the lowland rivers of Central Europe

The pattern of microhabitat preferences of Ukrainian brook lamprey Eudontomyzon mariae ammocoetes was examined in two rivers of central Poland: the Pilica River (the Vistula River basin) and the Grabia River (the Odra River basin). A comparison of abiotic factors of the rivers revealed differences in water speed and principal components: PC1 (determining gradient from decreasing medium sand to the increasing share of three fractions of gravel), PC2 (a gradient from the declining share of very coarse and coarse sand fractions to the growing content of fine sand) and PC3 (correlated with an increasing proportion of silt). The sites did not differ significantly in terms of water depth. Relative abundance and frequency of ammocoete occurrence in the Grabia River were higher than in the Pilica River. Only speed, PC1 and PC2 made a significant contribution to the prediction of larval occurrence. Eudontomyzon mariae larvae preferred substrata with a reduced amount of medium sand and increased content of gravel (PC1) as well as with a lower content of coarse sand and higher proportion of fine‐grained sand (PC2). The ammocoetes also preferred areas with a water speed of 0·2 m s^?1 but avoided speeds ≥0·6 m s^?1. The abundance of E. mariae was affected by water speed, as well as by all PCs. The mean ± s.e. optimal current speed was 0·265 ± 0·007 m s^?1, while abundance decreased with increasing amounts of gravel (PC1) and increased with increasing amounts of fine sand and silt in the bottom substratum (PC2 and PC3). Comparison of ammocoete microhabitat use in the Pilica and Grabia Rivers showed the lack of differences in distribution in the preferred values of current speed, PC1 and PC2.     

The effects of sediment type on growth rate and shell allometry in the soft shelled clam Mya arenaria L

Hatchery-reared juvenile Mya arenaria L. were grown for 11 wk in replicated gravel, sand, mud, and pearl net treatments under flow-through sea-water conditions in Maine. Analyses of variance showed significant differences between sediment treatments for final shell length, dry meat weight, chondrophore growth increment, and percent shell weight. Growth of juvenile M. arenaria was more rapid in fine sediments than in coarse sediments or nets.Regression slopes of shell length-shell height and shell length-shell depth varied significantly between sediment treatments. Slower-growing clams from nets and gravel were more globose than clams from sand or mud treatments. Clams grown in sand were longer and narrower than those from mud. Differences in growth rates and shell form were attributed primarily to the physical properties of the substrata, and their effects on the scope for growth of M. arenaria.     

Is there competition among ciliates and nematodes?

1. Biotic interaction between the ciliate Cyclidium glaucoma and the nematode Caenorhabditis elegans was investigated by manipulating the densities of the organisms in microcosms with and without sediment. 2. After 11 days the abundance of ciliates, nematodes and bacteria as well as extracellular enzyme activity were determined. Ciliates had a negative effect on nematode abundance in microcosms without sediment and in microcosms with sandy sediment, whereas in muddy sediment the effect was less distinctive. An effect of nematodes on ciliates was not observed. 3. The common resource bacteria were not affected negatively by the activity of the grazers. Overall grazer biomass increased with the addition of sediment to the microcosms, suggesting a rise of the carrying capacity in the experimental system. Especially in muddy sediment the abundance of bacteria and extracellular enzyme activity was higher compared to the microcosms without sediment. 4. The results of the experiment suggest a strong interspecific competition between nematodes and ciliates, where nematodes are, at least temporary, strongly affected.     

Genome-wide RNAi screening in Caenorhabditis elegans

In Caenorhabditis elegans, introduction of double-stranded RNA (dsRNA) results in the specific inactivation of an endogenous gene with corresponding sequence; this technique is known as RNA interference (RNAi). It has previously been shown that RNAi can be performed by direct microinjection of dsRNA into adult hermaphrodite worms, by soaking worms in a solution of dsRNA, or by feeding worms Escherichia coli expressing target-gene dsRNA. We have developed a simple optimized protocol exploiting this third mode of dsRNA introduction, RNAi by feeding, which allows rapid and effective analysis of gene function in C. elegans. Furthermore, we have constructed a library of bacterial strains corresponding to roughly 86% of the estimated 19,000 predicted genes in C. elegans, and we have used it to perform genome-wide analyses of gene function. This library is publicly available, reusable resource allowing for rapid large-scale RNAi experiments. We have used this library to perform genome-wide analyses of gene function in C. elegans. Here, we describe the protocols used for bacterial library construction and for high-throughput screening in C. elegans using RNAi by feeding.     

The food and feeding habits of five freshwater and brackish-water fish species in Nigeria

The food and feeding habits of five economically important fresh-and brackish-water fishes, Channa obscura, Chrysichthys nigrodigitatus, Heterotis niloticus, Synodontis nigrita and Trachinotus maxillosus, were investigated. A number of techniques were used to carry out gut content analysis, including the Hynes 'point' system based on volume estimations expressed as relative percentages. Juveniles of C. nigrodigitatus were omnivorous, consuming 32% gastropods, 30% nematodes, 14% diatoms and 8% crustaceans, while adults were planktotrophic, consuming 23% diatoms, 33% Chlorophyceae and 22% crustaceans. Synodontis nigrita juveniles fed almost exclusively (91%) on nematodes, while adults were predominantly planktotrophic, their diet comprising 50% diatoms and 50% crustaceans. Trachinotus maxillosus was exclusively benthotrophic, consuming 99.5% gastropods and 0.46% nematodes. Heterotis niloticus was planktotrophic at the adult stage and consumed 72% crustaceans, 12% gastropods, 3% fish and about 90% planktotrophic at the juvenile phase. Chrysichthys obscura was purely benthotrophic at the juvenile stage, feeding 100% on nematodes, but fed mainly (89%) on fish at the adult stage.     

An experimental protocol to select nematode species from an entire community using progressive sedimentary enrichment

The purpose of this study was to introduce free-living marine nematodes to the ‘world of biomarkers’. Biomarkers are still not used in the monitoring and assessment of this highly diverse phylum, because the technique needs to be applied at the single species level. This incurs high costs and involves time-consuming procedures, which are currently the main pitfalls when it comes to the application of these techniques to marine nematodes. Consequently, this work proposes an innovative protocol for selecting a single species from an entire community of nematodes using two independent selection processes whereby the sediment of the microcosms is progressively and separately enriched with fine and coarse sediment fractions. During our experiment, the abundance and number of nematode species decreased discernibly with exposure to both finer and coarser sediment. Multivariate analyses revealed that deposit- and epigrowth-feeders were the most tolerant feeding guilds, probably due to their deposit-feeding and microvore behaviours. At the end of the experiment, Terschellingia longicaudata and Ptycholaimellus ponticus became the unique members of the community when the sediment was enriched with fine and coarse sediment particles, respectively. After the complete alteration of the community, and when the mono-species level had been achieved, it was possible to maintain these two species alive, and without any drop in numbers, under the same laboratory conditions considered during the selection process. Accordingly, the protocol adopted here lays new foundations for the study of nematodes in the biomarker field.     

Suppression of nematophagous fungi by enchytraeid worms: a field exclosure experiment

The feeding biology of Enchytraeus crypticus and other enchytraeids is poorly understood as is their effect on nematophagous fungi. Because enchytraeids had been associated with nematophagous fungi in the field and had suppressed these fungi in soil microcosms, we tested the hypothesis that exclusion of enchytraeids, largely E. crypticus, would improve establishment of certain nematophagous fungi in field plots. The fungi, Hirsutella rhossiliensis and Monacrosporium gephyropagum, are being studied as potential control agents of plant-parasitic nematodes and were formulated as hyphae in alginate pellets. The pellets were mixed into soil without enchytraeids and placed in cages (PVC pipe, 80 cm³ volume) with fine (20 μm) or coarse (480 μm) mesh; cages were buried 15 cm deep in field plots and then recovered after 6–52 days. When fine mesh was used, enchytraeids were excluded and the fungi increased to large numbers. When coarse mesh was used, enchytraeid numbers in cages increased rapidly and the fungi did poorly. Although mesh also affected other potential fungivores, including collembolans and large dorylaimid nematodes, we suspect that enchytraeids were more important because large numbers were consistently found in cages with coarse mesh soon after the cages were placed in soil. Organisms smaller than enchytraeids (bacteria, fungi, and protozoa) also appeared to be important because the fungi did better in heat-treated soil than in non-heat-treated soil, regardless of mesh size. The rapid increase in enchytraeid numbers in cages with hyphal pellets and coarse mesh was probably caused by movement of enchytraeids toward the pellets with hyphae: increase in enchytraeid numbers was minimal when movement into cages was blocked (or when cages contained pellets without hyphae). Overall, the data were consistent with the hypothesis that enchytraeids, or other meso- or macrofauna, contributed to suppression of nematophagous fungi in our field plots. Received: 22 April 1997 / Accepted: 16 June 1997     

On the karyology of Dugesia gonocephala s.l. (Turbellaria,Tricladida) from Montpellier,France

Two species belonging to the Dugesia gonocephala group are found in the area of Montpellier, France. The karyology of these two species, D. gonocephala s. str. and S. subtentaculata, and of fissiparous Dugesia races has been studied.Two populations belonging to D. gonocephala s. str. are diploids with a chromosome number of 16, whereas the specimens of a third population are sexual aneuploids; the majority of cells possess 24 chromosomes, but some cells contain 23 or 25. The specimens attributable to D. subtentaculata are triploids, the most notable karyological feature being the presence of a single unmatched acrocentric chromosome. The fissiparous Dugesia strains are all aneuploids, the most common chromosome number being 27 with up to three small B-chromosomes.     

Food quality influences habitat selection in Daphnia

1. The vertical distribution of Daphnia in stratified lakes strongly depends on the depth profiles of temperature and food resources. However, ecological requirements for these factors are slightly different for juvenile and adult Daphnia. 2. Here, I investigated whether food quality influences the habitat selection of Daphnia pulicaria at night and whether the habitat selection of juvenile and adult D. pulicaria is different. Daphnia were allowed to choose their optimal habitat in large, stratified water columns (plankton towers, Plön) that held either the green alga Scenedesmus obliquus (high quality) in the cold hypolimnion (Hypo‐treatment) or S. obliquus in the warm epi‐ and cold hypolimnion (SCEN‐treatment) or the non‐toxic cyanobacterium Synechococcus elongatus (low quality) in the warm epilimnion and S. obliquus in the cold hypolimnion (SYN treatment). 3. When food (S. obliquus) was present only in the hypolimnion (Hypo‐treatment), juveniles and adults distributed similarly in the water column and spent most of their time in the interface between the warm and the food rich layer. 4. When food was present in the epilimnion and hypolimnion (SCEN‐ and SYN‐treatments), juvenile and adult D. pulicaria moved into the warm and now also food‐rich epilimnion, however, the magnitude of this shift depended on the food type and age class of Daphnia. Adult and juvenile D. pulicaria spent most of their time in the epilimnion when food there was of a high quality (S. obliquus; SCEN‐treatment). However, compared to the juveniles, adult Daphnia spent significantly more time in the colder hypolimnion when epilimnetic food was of a low quality (S. elongatus; SYN‐treament). 5. Therefore, habitat selection of adult D. pulicaria was affected by food quality whereas the habitat selection of juveniles was not. 6. Additional growth and reproduction experiments show that the food quality is likely to be responsible for the different habitat selection of juveniles and adults in the SYN‐treatment. 7. In conclusion, my experiments show that D. pulicaria behaviourally reacts to the quality of its food source.     

Observations on the clypeasteroid Echinocyamus pusillus (O. F. Müller)

The tiny echinoid Echinocyamus pusillus (O. F. Müller) is equipped with specialized external structures that suit it for a wide variety of environments. Special features include the ability to burrow in sediments of fine sand to shell gravel and to climb vertically.Specimens dredged off the west coast of Scotland were observed in aquaria and with the SEM. E. pusillus is characterized by three kinds of spines, and by two of pedicellariae. In contrast to sand dollars, the spines play a passive rôle in the feeding and burrowing operation, probably retaining a defensive nature as in the regular urchins. It is the podia that are chiefly involved in climbing, burrowing, righting, and probably feeding. Surface ciliary currents transport particles, but not to the mouth; they may have a respiratory or cleansing function. Experimental animals did not burrow in either very fine or very coarse sand, probably because a certain relationship exists between particle weight and podia size.E. pusillus shares behavioural and structural characteristics with regular and irregular urchins. It is not a true sand dollar, but may illustrate an evolutionary stage towards such a form.     

The karyotypes of Dugesia species from Spain (Turbellaria,Tricladida)

Some species of Planarians, new to Spain, are recorded. Dugesia polychroa, D. sicula, D. iberica and D. gonocephala s. 1. have been investigated karyologically. The former possesses a diploid complement characteristic of the biotype A (2n = 8); the second is diploid with 2n = 18; diploidy and triploidy were found in sexual populations of D. iberica with n = 8. Triploidy occurred in all the asexual strains of the D. gonocephala group with a basic number of either 8 or 9. In this latter case B-chromosomes were occasionally found.     

Microdistribution of macroinvertebrates in lowland streams

Summary Most benthic macroinvertebrate species are related to substrates types. Three main groups of species can be distinguished, each consisting of species with a similar preference for coarse mineral substrate (gravel), fine mineral substrate (sand) and organic material (leaves and/or coarse detritus), respectively. The particle size of the mineral component of the substrate, as well as the amount and the nature of the organic detritus, and the various combinations of both components, influence the microdistribution of most of the investigated species. Factors related to the substrate (e.g. oxygen and current conditions and food availability) are also important.     

Consequences of variation in species diversity in a community of root-feeding herbivores for nematode dynamics and host plant biomass

To date, no study has explicitly addressed effects of variation in species diversity of root‐feeding herbivores on host plant biomass. Root‐feeding nematodes typically occur in multi‐species communities. In a three‐year field experiment, we investigated how variation in species diversity of root‐feeding nematodes affected nematode dynamics and response of the dune grass Ammophila arenaria to root‐feeder activity. This plant species needs regular burial by fresh beach sand to remain vigorous, suggesting that A. arenaria benefits from a temporary escape from root‐feeding soil organisms and that root‐feeders are involved in plant degeneration in stabilized dunes. We created series of ceased and continued sand burial and added the endoparasitic nematodes Meloidogyne maritima, Heterodera arenaria and Pratylenchus penetrans alone or in combination to A. arenaria. We included treatments with and without the whole soil community, measured plant biomass and quantified numbers of nematodes. Addition of H. arenaria and P. penetrans decreased numbers of M. maritima juveniles and delayed the first appearance in time of both juveniles and females, while numbers of males only decreased when plants had been buried. Burial with sand and addition of the other two endoparasites affected numbers of H. arenaria juveniles, while numbers of P. penetrans were low and not affected. Shoot biomass of A. arenaria was lower when M. maritima had been added alone than when the three species had been added together. Addition of root zone soil decreased biomass of all plant parts. Burial with sand decreased aboveground shoot biomass, whereas it increased belowground shoot and root biomass. Our results point at idiosyncratic effects of nematode diversity on A. arenaria biomass. Heterodera arenaria and P. penetrans protected their host by reducing numbers and delaying activity of M. maritima to a later stage in the growth season, when root‐feeding activity was less harmful for plant biomass development.     

The role of fine sediment characteristics and body size on the vertical movement of a freshwater amphipod

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Association with pathogenic bacteria affects life‐history traits and population growth in Caenorhabditis elegans

Determining the relationship between individual life‐history traits and population dynamics is an essential step to understand and predict natural selection. Model organisms that can be conveniently studied experimentally at both levels are invaluable to test the rich body of theoretical literature in this area. The nematode Caenorhabditis elegans, despite being a well‐established workhorse in genetics, has only recently received attention from ecologists and evolutionary biologists, especially with respect to its association with pathogenic bacteria. In order to start filling the gap between the two areas, we conducted a series of experiments aiming at measuring life‐history traits as well as population growth of C. elegans in response to three different bacterial strains: Escherichia coli OP50, Salmonella enterica Typhimurium, and Pseudomonas aeruginosa PAO1. Whereas previous studies had established that the latter two reduced the survival of nematodes feeding on them compared to E. coli OP50, we report for the first time an enhancement in reproductive success and population growth for worms feeding on S. enterica Typhimurium. Furthermore, we used an age‐specific population dynamic model, parameterized using individual life‐history assays, to successfully predict the growth of populations over three generations. This study paves the way for more detailed and quantitative experimental investigation of the ecology and evolution of C. elegans and the bacteria it interacts with, which could improve our understanding of the fate of opportunistic pathogens in the environment.     

Effect of Soil Texture on the Distribution and Infectivity of Neoaplectana carpocapsae (Nematoda: Steinernematidae)

The vertical migration of N. carpocapsae infective juveniles applied to the soil surface or introduced 14 cm below the soil surface was studied in four different soil types (pure silica sand, coarse sandy loam, silty clay loam, and clay). The percentage of juveniles able to migrate and infect wax moth pupae placed in the soil decreased as the percentage of clay and silt increased. Most nematodes placed on the soil surface remained within 2 cm of the surface, but some penetrated to a depth of 10 cm in pure silica sand and coarse sandy loam to infect pupae. Some pupae at the same depth were also infected with nematodes in silty clay loam soil. In pure silica sand and coarse sandy loam, nematodes introduced 14 cm below the soil surface were able to infect wax moth pupae located between 4 and 24 cm. Movement was least in clay soil and limited in silty clay loam. Nematodes showed a tendency to disperse upwards from the point of application. In all cases the number of migrating nematodes was greatest when wax moth pupae were present.     

The mode of dislocation ofAstropecten aranciacus

Summary 1. The mode of dislocation of the sea starAstropecten aranciacus was investigated on 23 individuals at the NE-coast of Sardinia. All were small to medium-sized representatives of the species; their radius (R) varied between 5 and 15 cm. The observations were carried out on 2 level sediments with different sand-grain diameter. Each sea star was followed for 30 min and its locations were recorded every minute.2.A. aranciacus does not move continuously. It stops intermittently for an average duration of 2 minutes. On coarse grained sand, stops occur more frequently than on fine grained sand.3. The average distance travelled in 30 min was 3.7 m on fine sand, 1.6 m on coarse sand. Including the stops, the cruising speed varied mostly between 0 and 20 cm/min on fine sand, and between 0 and 10 cm/min on coarse sand.4. Generally, the observed paths were all or partially straight. In accord with this, the ratio W/D between the distance travelled (W) and the shortest between the starting and end position (D) was smaller than 2 for most animals.5. Small ripple marks (on fine sand) do not seem to influence the direction of dislocation. Single observations indicate, however, that more pronounced ripple marks (on coarse sand) may have an influence.

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Die Dislokationsweise vonAstropecten aranciacus

Kurzfassung An der Nordküste Sardiniens wurden auf einer Sandfläche in 8 m Tiefe Exemplare des SeesternsAstropecten aranciacus einzeln während einer 30minütigen Beobachtungsdauer verfolgt. Jede Minute steckte ein Taucher eine numerierte Steckmarke eine Handbreite hinter dem sich fortbewegenden Seestern in den Sand. Nachher wurden die Wege vermessen. Auf diese Weise wurden 23 Seesterne verfolgt. Die Auswertung der Beobachtungsdaten erbrachte Aufschlüsse über Wegrichtung und Richtungsänderung, Geschwindigkeit der Fortbewegung, Häufigkeit und Dauer des Anhaltens, Einfluß der Sandkorngröße auf Haltefrequenz und Geschwindigkeit der Fortbewegung und Einfluß des Verlaufs und der Höhe von Rippelmarken auf die Wegrichtung.

     

Effect of Soil Texture on the Distribution and Infectivity of Neoaplectana glaseri (Nematoda: Steinernematidae)

The vertical migration of infective juveniles of Neoaplectana glaseri applied to the soil surface or introduced 16 cm below the soil surface was studied in pure silica sand, coarse sandy loam, silty clay loam, and clay. The number of juveniles that migrated and infected wax moth pupae placed in the soil decreased as the proportion of clay and silt increased. The majority of nematodes moved downwards 2-6 cm from the surface, but some penetrated to a depth of 14 cm in pure silica sand and coarse sandy loam. In pure silica sand and coarse sandy loam, nematodes introduced 16 cm below the soil surface were able to infect wax moth pupae located at depths of 0-4 cm and 28-32 cm. Nematodes showed a greater tendency to disperse downwards from the point of application. Movement of the nematode was least in clay soil and limited in silty clay loam soil. The number of migrating nematodes was greatest when wax moth pupae were present.     

The freshwater planarian Dugesia sicula Lepori from Sardinia (Platyhelminthes,Tricladida)

Fissiparous strains of freshwater triclads of the Dugesia gonocephala group were collected from 12 localities in Sardinia all situated not more than 5 kilometers from the coast. Some environmental factors and the sexual status of the specimens were noted at the time of collection. During the laboratory rearing 30% of individuals of each strain became sexual (ex-fissiparous individuals). All the examined strains showed common karyological and morphological characteristics suggestive of the species Dugesia sicula Lepori. The chromosome complement, which was a constant 27+2–3 B chromosomes, was classified as aneutriploid, due to its clearly documented characteristics. The fissiparous populations of D. sicula appear to have a high degree of tolerance to variations in environmental factors, especially temperature. Within the D. gonocephala group this species has the broadest distribution in the Mediterranean region.     

Abundance, distribution and feeding relations of root/fungal feeding nematodes in a Scots pine forest

In a 15–20 yr old forest of Pinus sylvestris, Tylenchus spp., Paratylemchus spp? and Malenchus tantulus were the most abundant stylet-bearing nematodes. Soil layers and ground cover affected the abundance. Mycophagy was observed for Tylenchus sp., M. tantulus, Aphelenchoides sp. and Tylencholaimus stecki. Feeding on roots of the forest grass, Deschampsia flexuosa was recorded for W. tantulus, Paratylenchus spp? and Rotylenchus sp. The latter fed also on pine roots. Connections occurred between feeding habits and field distribution. The facultative feeding habit of M. tantulus probably allowed this species to reach higher numbers under D. flexuosa. The importance, in the field, of the grass Calamagrostis arundinacea for Paratylenchus spp? was confirmed by laboratory experiments. As pine was a non-host, these nematodes were probably grass feeders. Paratylenchus spp? dominated the obligate root feeders with forest grass being a key-factor for the group abundance. Suspected high densities of Paratylenchus spp? on clearings should not affect the growth of pine seedlings and although Rotylenchus sp. to some extent reduced seedling growth its pathogenic status on P. sylvestris was doubtful.