Embryonic and larval development of the basal ganglia connections in the brain of Xenopus laevis.
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Animals↗
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Intermediate hosts and larval development of Moniezia benedeni (Moniez 1879) in India.
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Animals↗
Effects of immunization of Pelibuey lambs with Oestrus ovis digestive tract protein extracts on larval establishment and development.
Larval midgut proteins of hematophagous parasites contain strong antigens that can be used for host immunization. This concept has been applied for immunization of Pelibuey sheep against Oestrus ovis L. (Diptera: Oestridae). The aim of this study was to examine the effect of immunization on larval establishment (LE) and development. Immunized lambs (I, n = 6) received two injections of crude gut membrane protein extracts (GMPE) from third instar larvae with Freund's incomplete adjuvant (FIA) on days 0 (Day of first immunization) and 21 (0.4 and 0.45 mg GMPE/lamb, respectively). The control group (C, n = 5) received physiological saline with FIA. Lambs were challenged with first instars on Day 29 (20 larvae) and Day 43 (25 larvae). Blood samples were collected biweekly and IgG titers were analyzed by ELISA. All lambs were slaughtered on Day 90 and number of larvae recovered, larval stage and larval weight were recorded at necropsy. No significant effect of immunization on LE (C = 28.9%; I = 31.0% P > 0.05) was observed. Antibody titers were higher in the immunized group on Day 28 (P < 0.05), but subsequently similar in both groups. Larval physiological age and weight were also significantly (P < 0.05) affected by immunization. Immunization of Pelibuey lambs with GMPE did not affect LE but did delay O. ovis larval development.
Animals↗
Development and larval morphology of Loa loa in experimental primate hosts.
Experimental infections with Loa loa were established in laboratory primates by inoculation of third-stage larvae recovered from either Chrysops silacea infected after engorging on a human volunteer with loiasis, or Chrysops atlanticus infected after blood feeding on experimentally infected primates. The third molt occurred at 16 to 20 days postinoculation of infective larvae, and the fourth at about 50 days. Early larval development was characterized by rapid growth and marked differentiation of the reproductive systems. Differences in the body's growth rate between the sexes were seen as early as 30 days and was especially marked by 60 days. Females grew more rapidly, and for a longer time than males. Males reach maximum size by 120 days, females not until about 300 days. Female worms were inseminated prior to day 90 developing eggs filled the uteri by 120 days, and microfilariae appeared in the peripheral blood at approximately 150 days. Morphological features of the larval and adult stages of human Loa loa are described.
Animals↗
Embryonic expression of engrailed in sea urchins.
Neural patterning genes that are expressed along the anterior-posterior axis of deuterostomes are expressed late in larval development in echinoderms and are thought to function in establishing the highly-derived, adult body plan. We have used genomic resources to clone an engrailed gene (SpEn) from Strongylocentrotus purpuratus, and with this we have developed an antibody specific for SpEn. SpEn is expressed late in embryogenesis in the developing larval nervous system. At the prism stage, a small number of neuroblasts in the oral ectoderm on the edge of the larval mouth begin expressing SpEn. The cells are in bilaterally symmetric positions. The expression of SpEn precedes the expression of the neural markers, synaptotagmin and serotonin in the SpEn immunoreactive cells. The SpEn cells are located on the margin of the domain of cells expressing SpNK2.1, but they do not have nuclear SpNK2.1. Expression of engrailed in a pair of bilateral neural structures in early development appears to be a shared feature of bilaterians.
Amino Acid Sequence↗
Comparative embryonic and larval developmental responses of estuarine shrimp (Palaemonetes pugio) to the juvenile hormone agonist fenoxycarb.
Grass shrimp (Palaemonetes pugio) were reared separately through both embryonic and total larval development during exposure to fenoxycarb at measured concentrations of <2.2 to 888 microg L(-1). A fenoxycarb concentration of 888 microg L(-1) significantly (p < 0.05) inhibited embryonic development to larval hatching and extended the embryonic developmental period from 11.9 to 12.7 days. Exposure to fenoxycarb concentrations < or = 502 microg L(-1) had no significant (p > 0.05) effect on complete embryonic development. Significantly fewer shrimp successfully metamorphosed to postlarvae when exposed through complete larval development to fenoxycarb concentrations > or = 4 microg L(-1). Larval development of grass shrimp was therefore >2 orders of magnitude more sensitive to this juvenile hormone agonist than was embryonic development. Viability of larvae developing in fenoxycarb was concentration dependent. Development beyond third zoeal stage was significantly inhibited at fenoxycarb concentrations > or = 190 microg L(-1), whereas development beyond fourth zoeal stage was inhibited by a concentration of > or = 45 microg L(-1). Fenoxycarb exposure of developing larvae did not alter either the duration of total larval development or the total number of larval stages before metamorphosis. Rearing of fenoxycarb-exposed embryos through larval development without further exposure had no significant effect on number of larval stages, larval development rate, or metamorphic success of larvae. Similarities in the sensitivity of grass shrimp larvae and mosquito larvae to fenoxycarb suggests that the use of a bioassay protocol measuring the metamorphic success of crustacean larvae would be a valuable adjunct to the hazard assessment of newly developed pesticides that target endocrine control of metamorphosis in insects and possibly other endocrine-disrupting xenobiotics as well.
Animals↗
Larval homologies and radical evolutionary changes in early development.
Larval forms are highly conserved in evolution, and phylogeneticists have used shared larval features to link disparate phyla. Despite long-term conservation, early development has in some cases evolved radically. Analysis of evolutionary change depends on identification of homologues, and this concept of descent with modification applies to embryo cells and territories as well. Difficulties arise because evolutionary changes in development can obscure homologies. Even more difficult, threshold effects can yield changes in process whereby apparently homologous features can arise from new precursors or pathways. We have observed phenomena of this type in closely related sea urchins that differ in developmental mode. A species developing via a complex feeding larva and its congener, which develops directly, have different embryonic cell lineages and divergent patterns of early development, but converge on the adult sea urchin body plan. Despite differences in embryonic developmental pathways, conserved gene expression territories are evident, as are territories whose homologies are in doubt. The highly derived development of the direct developer evidently arises from an interplay of novel organization of the egg, loss of expression of regulatory gene involved in production of feeding larval features, and changes in site and timing of expression of a number of genes.
Adaptation, Biological↗
The polychaete Platynereis dumerilii (Audouin and Milne-Edwards): a new species for assessing the hazardous potential of chemicals in the marine environment.
The polychaete Platynereis dumerilii (Polychaeta: Nereidae) has been evaluated as a candidate bioassay species for marine ecotoxicity testing. The species conforms with many of the requirements of an ideal bioassay organism in that (i) it is amenable to laboratory culture, (ii) its relatively small size makes it convenient for handling and laboratory exposure studies, (iii) its diet is defined and can be controlled, (iv) it reproduces throughout the year and, using photoperiod manipulation, can be induced to spawn as required, and (v) it has a short life cycle (approximately 3 months at 20 degrees C) making it feasible to study the effects of xenobiotics on chronic endpoints such as reproduction. The components of the life history which have been examined to date include fertilization rate, embryo-larval development, and larval survival. These life stages were evaluated using the reference materials used in the 1991 International Paris Commission (PARCOM) Ring Test (namely, the biocides, Bioban P-1487 and Vantocil IB, and the widely used reference toxicant, 3,5-dichlorophenol). For fertilization rate, the median effect concentrations (1-h EC50 values) were 0.32 mg.liter-1 for Bioban P-1487, 1.92 [corrected] mg.liter-1 for 3,5-dichlorophenol, and 9.66 mg.liter-1 for Vantocil IB. For embryo-larval development, the median effect concentrations (48-h EC50 values) were 0.29 mg.liter-1 for Bioban P-1487, 2.13 mg.liter-1 for 3,5-dichlorophenol, and 4.81 mg.liter-1 for Vantocil IB. For larval survival, the median lethal concentrations (48-h LC50 values) were 0.32 mg.liter-1 for Bioban P-1487, 3.64 mg.liter-1 for 3,5-dichlorophenol, and 10.9 mg.liter-1 for Vantocil IB. These results (all based on nominal values) suggest that, for these reference materials, the early life stages of P. dumerilii are of similar sensitivity to other marine invertebrate species. Together with the amenability of this species to laboratory culture, these data suggest that P. dumerilii has significant potential for use in marine ecotoxicity testing.
Animals↗
Multiple function of poxn gene in larval PNS development and in adult appendage formation of Drosophila.
The gene pox-neuro (poxn), which encodes a transcriptional regulator including a paired domain, specifies the differences between mono-innervated external sensory (m-es) organs and poly-innervated external sensory (p-es) organs in Drosophila. Here, we analyse the function of poxn in the development of the larval peripheral nervous system (PNS) and in other developmental aspects using a loss-of-function mutant of poxn. We observed that, in addition to the transformation of p-es into m-es organs in the mutant embryo, the external structure of the trichome-like sensilla (hairs) misdifferentiates into that of the campaniform-like sensilla (papillae) in the second and third larval instars. We also observed that POXN is expressed in a cell associated with the external structure of the trichome-like sensilla in the first and second instar larvae. These results imply that poxn is required in two distinct steps in the development of the larval PNS: (1) development of the larval p-es organs during embryogenesis and (2) re-formation of larval sensory hairs after each larval moult. In addition to its expression in the developing PNS, POXN is also expressed in concentric domains of the leg and antennal imaginal discs of early third instar larvae, and in the region of the wing disc that will form the wing hinge. The loss of poxn function results in defects of segmentation of the tarsus and antenna and in a distortion in the wing hinge. These results indicate that the poxn gene plays crucial roles in the morphogenesis of the appendages, in addition to its role in the early specification of neuronal identity.
Animals↗
Anthelmintic activities of fenbendazole against Nematodirus helvetianus in cattle: effect on egg production, embryogeny, and development of larval stages.
Calves experimentally infected with Nematodirus helvetianus were treated with a single dose of fenbendazole at the rate of 5 mg/kg of body weight. Fenbendazole was found to have an efficacy of 97.4% against adult N helvetianus. Additionally, eggs recovered 12 hours after calves were given the anthelmintic had fewer and frequently abnormal blastomeres. Fewer eggs were evident at 36 hours after treatment, and none was found at 72 hours or later. On the culturing of eggs from manure passed at 12 hours and later, almost no larval stages developed.
Animals↗
Climate change and the epidemiology of protostrongylid nematodes in northern ecosystems: Parelaphostrongylus odocoilei and Protostrongylus stilesi in Dall's sheep ( Ovis d. dalli ).
We describe the epidemiology of the protostrongylid parasites Parelaphostrongylus odocoilei and Protostrongylus stilesi in Dall's sheep (Ovis dalli dalli) from the Mackenzie Mountains, Northwest Territories, Canada (65 degrees N; 128 degrees W). Peak numbers of 1st-stage larvae of both parasites were shed by Dall's sheep on their winter range from March until May. In larval development experiments in the Mackenzie Mountains, peak numbers of infective 3rd-stage larvae of P. odocoilei were available in gastropod intermediate hosts in August-September. For both protostrongylids, the majority of transmission likely occurs on the winter range, with infection of gastropods when they emerge from hibernation in spring, and infection of Dall's sheep upon their return in fall. We validated a degree-day model for temperature-dependent development of larval P. odocoilei in gastropods, and applied degree-day models to describe and predict spatial and temporal patterns in development of P. odocoilei and P. stilesi in northern North America. Temperature-dependent larval development may currently limit northward range expansion of P. odocoilei into naïve populations of Dall's sheep in the Arctic, but climate warming may soon eliminate such constraints. In Subarctic regions where both P. odocoilei and P. stilesi are endemic, the length of the parasite 'growing season' (when temperatures were above the threshold for larval development) and amount of warming available for parasite development has increased over the last 50 years. Further climate warming and extension of the seasonal window for transmission may lead to amplification of parasite populations and disease outbreaks in host populations.
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Behavioral and developmental homeostasis in the fire ant, Solenopsis invicta.
The von Bertalanffy rule (1960) predicts that low incubation temperature during larval development will result in larger adult body size. If larval development in social insects followed this rule, then low incubation temperature would induce the development of larger workers and possibly even sexuals. To test this prediction, the effect of incubation temperature on larval development, larval meal size, larval tending and worker recruitment to food in the fire ant, Solenopsis invicta was investigated. Temperatures tested where within the range at which brood remains viable.Contrary to the predictions of the von Bertalanffy rule, worker size was unaffected by incubation temperature, and sexuals were reared at the high rather than the low incubation temperature. Moreover, larval meal size, the rate of larval tending by workers and the total number of workers recruited to food were unaffected by temperature.Mechanisms regulating developmental and behavioral homeostasis were as follows: the duration of larval development and the rate of larval growth changed proportionately with temperature such that the mean and variation of pupal size was unaffected by incubation temperature. Larvae solicited at the same rate, swallowed at the same rate and swallowed for the same duration such that meal size was unaffected by incubation temperature. On the brood pile, fewer workers tended brood at higher incubation temperatures, but worker tempo increased; as a result, brood tending was not adversely affected by incubation temperature. The rate of worker recruitment to food sites outside the nest increased with temperature, but the duration of the recruitment effort decreased such that, over time, the same total number of workers was employed to retrieve food.Incubation humidity was also investigated. When brood chambers were less than 100% humid, workers recruited to food and tended larvae (retrieved, sorted and groomed them), but did not feed larvae. Eventually, larvae died of starvation and were cannibalized.
Journal Article↗
Temporally regulated protein synthesis in cultured haemocytes of the Mediterranean fruit fly Ceratitis capitata during larval and prepupal development: internalization of larval serum proteins into the haemocytes.
Detailed analysis of haemocyte proteins by one-dimensional polyacrylamide gel electrophoresis during the late larval stages and white pupae of the Mediterranean fruit fly Ceratitis capitata reveals more than 50 polypeptides. A numbering system is established based on molecular weight on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Detailed examination leads to the conclusion that each protein resolved by our methods has its own characteristic kinetics of accumulation. The most abundant protein is unequivocally the 36-kDa band with an isoelectric point at 5.07, followed by the 47- and 54-kDa proteins. The 36-kDa band constitutes approximately 9% of total haemocyte protein. Comparison of the haemocyte protein pattern to that of cell-free haemolymph clearly shows that the protein bands at 81, 82, 85, and 87 kDa are common in both sources. We demonstrated by immunoblotting and pulse-labeled experiments followed by 2D SDS-PAGE that these protein bands which constitute the larval serum proteins were internalized into the haemocytes from the serum. By pulse labeling cells with [35S]methionine, separating polypeptides by one-dimensional PAGE electrophoresis, and comparing the rates of synthesis of over 50 individual polypeptides by fluorography, the following results were obtained: Three protein groups with distinct patterns of synthesis were noted: (1) proteins that are synthesized throughout the developmental period studied, (2) proteins whose synthesis begins at the wandering stage, and (3) proteins that are synthesized only during the feeding period. The 47-kDa protein shows the highest relative rate of synthesis, but since it is not the most accumulated band it must have a high turnover rate. Most of the labeled proteins were secreted into the incubation medium. The intracellular transit time was estimated to be about 11 min. Patterns of protein synthesis in haemocytes are regulated in a precise temporal sequence during the transformation of larvae to pupae. Their study yields a useful system for the analysis of molecular events in gene control.
Animals↗
Failed recruitment of southern toads (Bufo terrestris) in a trace element-contaminated breeding habitat: direct and indirect effects that may lead to a local population sink.
We conducted a transplant study in which embryonic southern toads (Bufo terrestris) were held in a site polluted with coal ash (site AB; containing As, Cd, Cr, Cu, Se, and other elements) and a reference site (site R) through hatching and early larval development. To examine the remainder of the larval period, surviving larvae in AB were then transplanted to R and back-transplanted to AB, whereas surviving larvae from R were back-transplanted to R. Survival through early larval development was lower in AB than in R (34% versus 50%). However, site of hatching did not influence traits later in development (larval metabolic rate, larval morphology, duration of larval period, size at metamorphosis, or average hopping distance by metamorphs). Toads that spent the entire larval period in R had high rates of survival (70-94% of individuals transplanted after the embryonic period) regardless of where they spent the embryonic and early larval period. However, toads held in AB for the duration of the larval period suffered 100% mortality. Algal resources were scarce and their trace element concentrations high in AB compared to R, suggesting that mortality of larval toads resulted from a combination of direct toxicity (via sediment- and foodborne exposure) and indirect effects on resource abundance. The study suggests that the widespread practice of disposing of coal ash in open aquatic basins may result in sink habitats for some amphibian populations.
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The negative effects of the residues of ivermectin in cattle dung using a sustained-release bolus on Aphodius constans (Duft.) (Coleoptera: Aphodiidae).
This paper reports the findings of two trials into the effects of the treatment of cattle with ivermectin slow-release (SR) bolus on the larval development of the dung beetle Aphodius constans Duft. Rectal faecal samples were collected prior to treatment and every 3 and 2 weeks in a first and second trial, respectively, and up to 156 days post-administration of the SR bolus. Faecal ivermectin concentration reached a peak at 63 days post-treatment (1427 ng g(-1)) and ivermectin was detected up to 147 days post-treatment in the first trial (7.2 ng g(-1)). First stage larvae of A. constans were reared with control or contaminated dung and adult beetles were counted after emergence. In the first trial, the comparison of pairwise samples showed that ivermectin prevented the development of larval A. constans until day 105, while at day 135 the rate of emergence was still significantly lower than the corresponding series of control (p < 0.05). In the second trial, the difference between control and treated series remained significant until 143 days post-treatment, with no emergence until 128 days post-administration of SR bolus to cattle. These results show the negative effect of ivermectin on the development of larval A. constans, even at a low concentration (38.4 ng g(-1)). The administration of ivermectin sustained-release bolus to cattle was highly effective in killing dung beetle larvae for approximately 143 days after treatment. The results were similar when dung was obtained from a single animal kept alone, or from a blending of faecal pats obtained from a group of animals kept in field conditions during the whole trial period.
Animals↗
Divergent patterns of neural development in larval echinoids and asteroids.
The development and organization of the nervous systems of echinoderm larvae are incompletely described. We describe the development and organization of the larval nervous systems of Strongylocentrotus purpuratus and Asterina pectinifera using a novel antibody, 1E11, that appears to be neuron specific. In the early pluteus, the antibody reveals all known neural structures: apical ganglion, oral ganglia, lateral ganglia, and an array of neurons and neurites in the ciliary band, the esophagus, and the intestine. The antibody also reveals several novel features, such as neurites that extend to the posterior end of the larva and additional neurons in the apical ganglion. Similarly, in asteroid larvae the antibody binds to all known neural structures and identifies novel features, including large numbers of neurons in the ciliary bands, a network of neurites under the oral epidermis, cell bodies in the esophagus, and a network of neurites in the intestine. The 1E11 antigen is expressed during gastrulation and can be used to trace the ontogenies of the nervous systems. In S. purpuratus, a small number of neuroblasts arise in the oral ectoderm in late gastrulae. The cells are adjacent to the presumptive ciliary bands, where they project neurites with growth cone-like endings that interconnect the neurons. In A. pectinifera, a large number of neuroblasts appear scattered throughout the ectoderm of gastrulae. The cells aggregate in the developing ciliary bands and then project neurites under the oral epidermis. Although there are several shared features of the larval nervous systems of echinoids and asteroids, the patterns of development reveal fundamental differences in neural ontogeny.
Animals↗
Effect of ovine urine and some of its components on viability of nematode eggs and larvae in sheep faeces.
Sheep faeces incubated for 7 days at 27 degrees C for cultivation of third-stage nematode larvae were sprinkled daily with urine from sheep or with solutions of components normally occurring in sheep urine. Larval development was completely blocked in cultures sprinkled either with sheep urine, with solutions of 2 or 4% urea, or with urine from which urea or the phenol components had been extracted. Only a few third-stage larvae developed in cultures sprinkled with 1% urea. Normal larval development occurred in cultures sprinkled with either the phenol component from urine, or with solutions of 0.035% phenol, 0.035% p-cresol, 0.3% allantoin, 0.3% hippuric acid or 2.8% NaCl. Normal larval development also occurred in all control cultures sprinkled with water, including one culture where there was urine in the space between the outer and inner beaker used for cultivation. It is suggested that the inhibitory effect of urine on larval development is mainly caused by ammonia produced when urinary urea is brought into contact with urease of faecal origin. It is, however, an unsolved question why urine, from which urea had been removed, also inhibited larval development.
Animals↗
Enhancement of development of larval Anopheles arabiensis by proximity to flowering maize (Zea mays) in turbid water and when crowded.
To determine whether proximity to flowering maize enhances the development of larval anopheline mosquitoes breeding in turbid water and when crowded, we evaluated the development of larval Anopheles arabiensis under various conditions of turbidity, larval density, and proximity to pollen-shedding maize in simulated breeding puddles in a malaria-endemic site. In naturally formed puddles, water turbidity, as well as larval density, increased as the rainy season progressed. In sites remote from flowering maize, more pupae developed and the resulting adults were larger in relatively clear water than in turbid water, and larval crowding inhibited development. In close proximity to flowering maize, however, larval development was little affected by water turbidity and larval crowding. Larvae of this member of the African An. gambiae complex of mosquitoes develop readily in turbid water and when crowded, provided that their breeding sites are located where maize pollen is abundant.
Animals↗