Growth In Nematodes Research Articles

Neonicotinoid-containing insecticide disruption of growth, locomotion, and fertility in Caenorhabditis elegans.

Neonicotinoids, a class of insecticides structurally similar to nicotine that target biting and sucking insects, are the most widely used insecticides today, in part due to their supposed low toxicity in other organisms. However, a growing body of research has found that even low doses of neonicotinoids can induce unexpected negative effects on the physiology and survival of a wide range of non-target organisms. Importantly, no work has been done on the commercial formulations of pesticides that include imidacloprid as the active ingredient, but that also contain many other components. The present study examines the sublethal effects of “Tree and Shrub”™ (“T+S”), a commercial insecticide containing the neonicotinoid imidacloprid as its active ingredient, on Caenorhabditis elegans. We discovered that “T+S” significantly stunted the overall growth in wildtype nematodes, an effect that was exacerbated by concurrent exposure to heat stress. “T+S” also negatively impacted fecundity as measured by increased germline apoptosis, a decrease in egg-laying, and fewer viable offspring. Lastly, exposure to “T+S” resulted in degenerative changes in nicotinic cholinergic neurons in wildtype nematodes. As a whole, these findings demonstrate widespread toxic effects of neonicotinoids to critical functions in nematodes.

Feasibility of using a standardized Caenorhabditis elegans toxicity test to assess nanomaterial toxicity.

Increasing production and use of engineered nanomaterials (ENMs) has generated widespread interest in measuring their environmental and human health effects. However, the lack of standardized methods for these measurements has often led to contradictory results. Our goal in this study was to examine the feasibility of using a standardized Caenorhabditis elegans growth and reproduction based toxicity test designed for use with dissolved chemicals to assess ENM toxicity. Sensitivity testing of seven key experimental factors identified by cause-and-effect analysis revealed that bacterial feed density and plate shaking had significant effects on growth inhibition by a reference toxicant, benzylcetyldimethylammonium chloride (BAC-C16). Bacterial density was inversely proportional to experimental EC50 values, while shaking the plates during the assay caused a substantial decrease in nematode growth and reproduction in control nematodes. Other factors such as bacterial viability, organism maintenance, and media type showed minimal effect on the test method. Using this assay with positively charged polystyrene nanoparticles (PSNPs) revealed that the variability in the PSNP EC50 values was larger compared to those of BAC-C16. Additionally, while media type and bacterial viability did not impact BAC-C16 toxicity, PSNP toxicity differed substantially when these parameters were changed. PSNPs were more toxic in K+ medium and S-basal compared to M9 and feeding nematodes with UV killed E. coli decreased toxicity of PSNPs. Test validity with ENMs and modifications that can be made to adapt the standard C. elegans toxicity assay for use with ENMs are discussed.

Comparison of toxicities from three metal oxide nanoparticles at environmental relevant concentrations in nematode Caenorhabditis elegans

Nematode Caenorhabditis elegans has been developed in a variety of environmental studies to address adverse effects of a wide range of toxicants. In the present study, we compared the toxicities of three metal oxide nanoparticles (NPs) including TiO2–NPs, ZnO–NPs, and SiO2–NPs with the same nanosize (30nm) after prolonged exposure from L1–larvae to adult at environmental relevant concentrations. Our data indicated that the adverse effects were detected in nematodes exposed to TiO2–NPs and ZnO–NPs at concentrations more than 0.05μg/L and SiO2–NPs at concentrations more than 5μg/L with locomotion behavior and ROS production as endpoints. With growth, locomotion behavior, reproduction, and ROS production as endpoints, toxicity order for the examined metal oxide NPs was: ZnO–NPs>TiO2–NPs>SiO2–NPs. In nematodes exposed to the examined metal oxide NPs, ROS production was significantly correlated with lethality, growth, reproduction, and locomotion behavior. Moreover, treatment with antioxidants of ascorbate or NAC effectively inhibited the formation of oxidative stress and retrieved the adverse effects of TiO2–NPs, ZnO–NPs, and SiO2–NPs on survival, growth, reproduction and locomotion behaviors in nematodes. Our data demonstrated the subtle toxicity differences of different NPs exposure at environmental relevant concentrations in C. elegans.

C. elegans metallothioneins: response to and defence against ROS toxicity

The genome of the nematode Caenorhabditis elegans encodes for two multifunctional metal binding metallothioneins (MTs), CeMT-1 and CeMT-2. Here we applied qPCR to identify a transcriptional up-regulation following the exposure to free radical generators (ROS) paraquat or hydrogen peroxide, a trend that was confirmed with Pmtl::GFP expressing alleles. The deletion of the MT loci resulted in an elevation of in vivo levels of hydrogen peroxide and exposure to ROS caused a reduction in total egg production, growth and life span in wild type nematodes, effects that were particularly pronounced in the CeMT-2 and double knockout. Moreover, in vitro incubation of recombinant MTs with hydrogen peroxide demonstrated the presence of direct oxidation of the CeMTs, with zinc released from both isoforms and concomitant formation of intra-molecular disulfides. Finally, metabolic profiling (metabolomic) analysis of wild type and MT knockouts in the presence/absence of oxidative stressors, confirmed the overall trend described by the other experiments, and identified 2-aminoadipate as a potential novel small-molecule marker of oxidative stress. In summary, this study highlights that C. elegans metallothioneins scavenge and protect against reactive oxygen species and potentially against oxidative stress, with CeMT-2 being more effective than CeMT-1.

Modelling nematode life cycles using dynamic energy budgets

Summary To understand the life cycle of an organism, it is important to understand the underlying physiological mechanisms of their life histories. We here use the theory of dynamic energy budgets (DEB) to investigate the close relationships between growth, reproduction and respiration in nematodes. Using a set of simplified equations based on DEB theory, we are able to accurately describe life‐cycle data from the literature for the free‐living bacterivorous nematodes Caenorhabditis elegans, C. briggsae and Acrobeloides nanus, under different temperature or food regimes. Nematodes apparently differ from other animals, as the initial growth is slower than expected. We explain this phenomenon by food limitation in the larvae, which is supported by more detailed physiological studies. Food density and temperature are shown to have predictable effects on the growth curves (temperature affects only growth rate, whereas food density also affects ultimate size), although the reproduction patterns reveal some deviations from model predictions. The presented model integrates the different aspects of the life cycle into a single framework, and can be applied as such to interpret the effects of various stressors.

Evolution of germ-line signals that regulate growth and aging in nematodes.

We show that a signal from the germ line represses growth in the nematode Caenorhabditis elegans. Laser-microbeam ablation of cells that give rise to the germ line causes adults to become giant. Ablation of these cells in self-sterile mutant worms also causes gigantism, suggesting that the germ line represses growth because it is the source of a growth-antagonizing signal rather than because of a sink of resources required for reproduction. The C. elegans germ line also emits a signal that represses longevity. This longevity-repressing signal requires the activity of DAF-16, a forkhead/winged-helix transcription factor, but we find that that the growth-repressing signal does not. The growth-repressing signal also does not require the activity of DBL-1, a transforming growth factor beta-related protein that promotes growth in worms. By ablating the germ-line precursors of other species of free-living nematodes, we also found that both the growth-repressing and longevity-repressing signals are evolutionarily variable. Some species have both signals; others have just one or the other. We suggest that variation in germ-line signaling contributes to body size and life-history diversity in the nematodes.

A novel mode of ecdysozoan growth in Caenorhabditis elegans.

Whereas growth in many ecdysozoa is associated with only molting, larval growth in nematodes, specifically Caenorhabditis elegans, is thought to be continuous and exponential. However, this has never been closely investigated. Here we report several detailed studies of growth in wild-type and dwarf C. elegans strains. We find that apparent exponential growth between hatching and adulthood comprises a series of linear phases, one per larval stage, with the linear growth rate increasing at successive molts. Although most structures grow continuously, the buccal cavity does not; instead, it grows saltationally at molts, like arthropod structures. We speculate that these saltational changes in mouth size permit changes in growth rate and that molting exists in nematodes to facilitate rapid growth. We study the cellular basis of this growth in the hypodermis. At each larval stage, lateral seam cells produce daughters that fuse with hyp7, a syncytium covering most of the worm. We find that seam cells and fusing daughter cells obtain larger sizes in successive molts. The total seam cell volume remains constant relative to the size of the worm. However, fusing daughter cells contributes only a very small amount directly to hypodermal growth, suggesting that most hyp7 growth must be intrinsic. Thus, dwarfism mutations studied principally act via adult syncytial growth, with cell size being near normal in both dbl-1 and dpy-2 mutant worms. We speculate that the main function of seam cell proliferation may be to supply the hypodermis with additional genomes for the purpose of growth.

Somatic polyploidization and cellular proliferation drive body size evolution in nematodes.

Most of the hypodermis of a rhabditid nematode such as Caenorhabditis elegans is a single syncytium. The size of this syncytium (as measured by body size) has evolved repeatedly in the rhabditid nematodes. Two cellular mechanisms are important in the evolution of body size: changes in the numbers of cells that fuse with the syncytium, and the extent of its acellular growth. Thus nematodes differ from mammals and other invertebrates in which body size evolution is caused by changes in cell number alone. The evolution of acellular syncytial growth in nematodes is also associated with changes in the ploidy of hypodermal nuclei. These nuclei are polyploid as a consequence of iterative rounds of endoreduplication, and this endocycle has evolved repeatedly. The association between acellular growth and endoreduplication is also seen in C. elegans mutations that interrupt transforming growth factor-beta signaling and that result in dwarfism and deficiencies in hypodermal ploidy. The transforming growth factor-beta pathway is a candidate for being involved in nematode body size evolution.

Gompertz growth in number dead confirms medflies and nematodes show excess oldster survival.

A recent report (Easton, 1995) showed that, at least for Mediterranean fruit flies, a Gompertz growth equation based on the increase in number of individuals that die is a better predictor of survival data than is the classical Gompertz survivorship model based on the decrease in number that survive (analysis of medfly data of Carey et al., 1992). In the growth model, the rate of increase of the number dead (i.e., the death rate) decreases exponentially with age. The poor fit of the classical model predicts "excess survival" of older members, but, when the scale of the better-fitting growth model is increased 2400x, such excess is now also evident as a small but distinctly separate cohort of the medfly subjects. The smaller population appears to be about 0.01% of the larger, and the death rate decreases about one-fourth as fast. Survival of the nematode C. elegans (Brooks et al., 1994) is also better predicted by the growth model, which also shows excess survival of the worms at great age.

Structure and expression of a novel filarial gene for glia maturation factor

Factors that influence neural growth and development in parasitic nematodes have not yet been identified. We have isolated and sequenced a Brugia malayi nematode 3.4-kb genomic DNA fragment and its corresponding cDNA, which encode a predicted protein of 138 amino acids with 52% identity and 75% similarity to the mammalian neuroglial growth factor, glia maturation factor-β (GMF). GMF promotes the differentiation of mammalian glia and neurons and stimulates axonal regeneration. The filarial nematode gene Bmgmf for Brugia malayi glia maturation factor contains six predicted exons, with the first exon encoding only the initiation methionine. Brugia malayi GMF (BmGMF) is also related to a large family of eukaryotic actin depolymerizing factors (ADFs). Although BmGMF does not contain the consensus actin-depolymerizing motif of ADFs, it does share a similar intron–exon structure, including the unusual first exon, with the unc-60 ADF gene of the nematode Caenorhabditis elegans. RT-PCR experiments reveal that BmGMF is trans-spliced with the nematode spliced leader sequence SL1 and is expressed in microfilariae but not in third-stage larvae or adult worms. We speculate that BmGMF may function as a stage-specific neuroglial growth factor.

Thermal time and ecological strategies ‐ a unifying hypothesis

SummaryRates of embryogenesis and of development and growth in several nematodes are linearly related to temperature over a considerable range. On this basis, published data on the thermal time requirements are compared for a tropical and a temperate species of plant parasitic nematode Meloidogyne javanica and M. hapla respectively, the two being closely related and morphologically and biologically similar. M. hapla has a lower base temperature (Tb) and a higher thermal constant (S) than M. javanica with the relative values being almost inversed. Consequently, above their respective Tb values the slope of the relationship between rate of development and temperature was greater for the tropical species than that for the temperate species. A mathematical exploration of the relationship between Tb and S was made assuming that, over a narrow range, Tb×S was a constant. With this assumption, for any given average environmental temperature (Te) the optimum base temperature for minimum developmental duration was Te/2, and the temperature at which the duration of development was equal for the otherwise identical species was shown to be the sum of their base temperatures. The practical effect of the differences in Tb and S was to give M. hapla, the temperate species, a shorter life cycle and hence a competitive advantage at temperatures below 21ÅC and M. javanica, the tropical species, the advantage above that temperature. It is argued that a negative correlation between Tb and S is likely to be widespread, and provides a mechanism for regulating the distributions of related, competing organisms. Support for the hypothesis that the value of S tends to decrease as Tb increases is derived from data on the embryogenesis of an animal parasitic nematode Haemonchus contortus and from seed germination studies. Contrary results and exceptions are also briefly discussed. The observed interaction between Tb and S may be fundamental to many poikilothermic organisms and plants and provides an explanation for tropical species generally having higher Tb values than temperate ones. The ecological implications of different values of Tb and of S, including their relationship with organisms which are “r” or “K” strategists are briefly discussed.

Growth, reproduction and longevity in nematodes from sewage treatment plants.

The growth, reproduction and longevity of Diplogasteritus nudicapitatus, Paroigolaimella bernensis and Rhabditis curvicaudata were investigated under conditions of excess food within the temperature range 5°C-20°C. In all three species growth rate increased with temperature, and in D. nudicapitatus and R. curvicaudata the adult size attained varied significantly with temperature. P. bernensis did not reproduce at 5°C, but showed a progressive increase in reproductive output at higher temperatures. D. nudicaitatus showed increased egg production as temperature increased while R. curvicaudata had maximum egg output at 10°C. Longevity is temperature dependent, decreasing with higher temperatures. Virgin females survived for longer than reproducing females. The data indicate that while D. nudicapitatus and P. bernensis are thermophilic species, R. curvicaudata is adapted to lower temperatures.

Growth and moulting in nematodes: moulting and development of the hatched larva of Rotylenchulus reniformis

SummaryThe morphology of the post-hatch moulting and developmental sequence of an amphimictic population of Rotylenchulus reniformis has been examined in living and fixed material. Under suitable conditions of temperature and in a moist environment the 2nd-stage larva (L2) undergoes a series of 3 moults and developmental changes which result in the formation of males and immature females. After hatching and prior to the start of the first of these moults (the second moult), there is a pre-moult period, usually of 3–5 days duration. The morphology of the entire moulting and developmental sequences, from L2 to just after the final moult, has been followed in single living specimens of a parasitic nematode using differential interference contrast optics, and sections cut through different stages have been observed under the transmission electron microscope. These moulting sequences (at 24 °C) take place at similar times in developing males and females. The second moult takes place on the second day after commencement of moulting, the third on the third or fourth days and the fourth and final moult on the sixth or seventh days, followed by further development over several days to give rise to the adult male and the immature female. The ultrastructure associated with some of the more obvious of these developmental changes is described and includes the morphology of the head region and cuticles of L2, L4, adult males and immature females, the oesophageal glands of the immature female and the copulatory spicules and spermatozoa of the male.

Postembryonic growth of Romanomermis culicivorax Ross and Smith, 1976: an example of accretionary growth in the Nematoda

The postembryonic development of Romanomermis culicivorax was studied in experimentally infected Aedes aegypti larvae. During its 7-day parasitic phase the nematode increased 8-fold in length and 10-fold in width, and the number of somatic nuclei increased 30-fold. Mitosis was observed in the hypodermal, trophosomal (intestinal), and muscle tissues. Body length and body width were correlated with number of somatic nuclei (r = +0.95, p < 0.001 and r = +0.91, p < 0.001 respectively). Growth in R. culicivorax is associated with extensive nuclear division, and this is believed to be the first report of accretionary growth in nematodes. The number of lateral hypodermal chord nuclei is variable in postparasitic juveniles and adults (mean, 1206 ± 536; range, 610–2475) and is correlated with body length (r = +0.84, p < 0.001). The lateral hypodermal chord nuclei do not undergo a fixed number of divisions.

Growth and moulting in nematodes: Changes in the dimensions and morphology of Rotylenchulus reniformis from start to finish of moulting

At a temperature of 24°C, freshly hatched second stage larvae (L 2) of Rotylenchulus reniformis take 2 weeks to complete moulting and become either adult males or immature females. Measurements of different nematode stages were made using a computer-interfaced digitizer (CID). This proved to be more rapid and reproducible than conventional techniques. Moulting and development were followed in individual living specimens viewed under Nomarski optics and oil immersion. The mean loss in body volume of these specimens from L 2 to immature female is about 17% compared with about 19% for the mean loss in body volume from L 2 to male. The mean volumes for a total of 70 randomly selected living specimens measured are 95·6 pi for L 2s, 72·9 pl for immature females and 74·2 pl for males. Mean losses in body volume during moulting calculated from these randomly selected stages were slightly higher than those observed for individuals, being about 24% for the immature female and about 22% for the male.

Growth and Form in Nematodes: Iii. Comparison of Oesophagus and Body Shape

The nematode body is characterized by a strong interaction between body length, body width and oesophageal shape. Several studies on the post-embryonic development of free-living, plant parasitic and animal parasitic nematodes reveal that the maintenance of a vermiform shape (width usually less than 4-5% of length) is necessary for motion and that a nematode can only lose its vermiform shape when it has not to move around hunting for food. The changes in body shape during post-embryonic development are intimately linked to the structure and changes in structure of the oesophagus: a bulbous oesophagus needs a wider body than a cylindrical oesophagus; on the other hand a bulbous oesophagus is usually much shorter than a cylindrical oesophagus. The well-known changes in body shape and oesophageal structure in animal and plant-parasitic nematodes will be explained according to the observations mentioned above.

Increase of rate of egg production with growth in some intestinal nematodes of sheep and horses

Ractliffe L. H. & LeJambre L. F. 1971. Increase of rate of egg production with growth in some intestinal nematodes of sheep and horses. International Journal for Parasitology, 1: 153–156. There is a positive relationship between the number of uterine eggs and size of worm in Chabertia ovina, Haemonchus contortus, Oesophagostomum columbianum, and Para-scaris equorum, and a linear relationship between the weight of the egg sac and the weight of the remainder of the worm in Oxyuris equi. These relationships imply that the rate of egg production increases with growth. Consequently it would be expected that (a) the total egg output of a population of parasites would be more closely related to the total weight of the worms than to their number and (b) there would be a logarithmic increase with time in the egg output of a newly infected host even if the increase in the number of worms harbored by the host were only linear with time.