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PubMed2005

Coexistence of three different Drosophila species by rescheduling their life history traits in a natural population.

We present evidence for coexistence of three different Drosophila species by rescheduling their life history traits in a natural population using the same resource, at the same time and same place. D. ananassae has faster larval development time (DT) and faster DT(egg-fly) than other two species thus utilizing the resources at maximum at both larval and adult stages respectively. Therefore, D. ananassae skips the interspecific competition at pre-adult stage but suffers more from intraspecific competition. However, D. melanogaster and D. biarmipes have rescheduled their various life history traits to avoid interspecific competition. Differences of ranks tests for various life history traits suggest that except for DT(egg-pupa), the difference of ranks is highest for the combination of D. melanogaster and D. ananassae for all other life history traits. This difference is maintained by tradeoffs between larval development time and pupal period and between pupal period and DT(egg-pupa) in D. ananassae.

Animals↗
PubMed1992

Cultivation of the third-stage larvae of Necator americanus in vitro.

When filariform larvae of Necator americanus, enclosed within the second sheath, were cultured in various semi-defined media, the best larval development was achieved in Waymouth's MB 752/1 with 20% foetal calf serum (FCS). In this medium, most of the filariform larvae cast off the second sheath and developed into third-stage larvae with provisional buccal capsules and some larvae developed further; 26% were fourth stage after 49 days of culture. Of several supplements tested, only FCS supported such development and no further development occurred if the medium was further supplemented with human red blood cells, liver extract, intestinal extract or tryptose phosphate broth. Larval development stopped at or before early third stage in Eagle's Basal Medium, F-12, NCTC 135 and L-15, even when these media were supplemented with FCS.

Animals↗
PubMedDate not supplied

Comparative helminth infections of man in two rural communities of the Niger Delta, Nigeria.

The intestinal parasitic helminth infections of man in Bonny and Isiokpo communities were studied between May 1992 and March 1994. Of the 2008 stool samples examined from Bonny community, 503 (25.0%) were infected. 305 (26.7%) of these infections were males while 198 (22.9%) were females. Ascaris lumbricoides (24.1%) occurred most frequently, followed by Hookworms (18.0%), Trichuris trichiura (17.3%,) Strongyloides stercoralis (10.1%) and Enterobius vermicularis (0.1%). Peak infection (41.7%) was recorded for the males in (10-14) years age bracket. The use of bush as a toilet facility had the highest parasitic infection (38.3%), followed by that of shoreline (35.3%), pit (33.3%), Bucket (27.8%) and of water closet (7.5%). Degree of infection relative to source of drinking water showed that well water was associated with highest infection (43.3%) while the pipe borne water was the lowest (18.0%). From Isiokpo community 2,462 stool samples were examined for intestinal parasites 1,633 (66.3%) people were infected consisting of 862 (64.8%) males and 771 (68.2%) females. Higher parasitic infection of females in this community was attributed to the cultural and occupational factors. Frequency of occurrence of individual helminth was as follows: A-lumbricoides (64.5%), T. trichiura (59.4%), Hookworms (58.8%), S. stercoralis (25.1%), Hymenolepsis nana (2.9%) and E. vermicularis (0.3%). Prevalence of infection was significantly higher in Isiokpo than in Bonny because the climatic and edaphic factors were conducive to larval development and infectivity. On the contrary, the saline soil and surface water of Bonny community constituted harsh environmental conditions inimical to larval development and infectivity. Observations on parasitic infections in relation to toilet facilities and source of drinking water were similar to those made in Bonny. The study therefore demonstrated that the provision of pipe borne water and water closet facilities in rural Niger Delta communities could reduce helminth infections of man.

Adolescent↗
PubMed2005

Field evaluation of anthelmintic drug sensitivity using in vitro egg hatch and larval motility assays with Necator americanus recovered from human clinical isolates.

A field-applicable assay for testing anthelmintic sensitivity is required to monitor for anthelmintic resistance. We undertook a study to evaluate the ability of three in vitro assay systems to define drug sensitivity of clinical isolates of the human hookworm parasite Necator americanus recovered from children resident in a village in Madang Province, Papua New Guinea. The assays entailed observation of drug effects on egg hatch (EHA), larval development (LDA), and motility of infective stage larvae (LMA). The egg hatch assay proved the best method for assessing the response to benzimidazole anthelmintics, while the larval motility assay was suitable for assessing the response to ivermectin. The performance of the larval development assay was unsatisfactory on account of interference caused by contaminating bacteria. A simple protocol was developed whereby stool samples were subdivided and used for immediate egg recovery, as well as for faecal culture, in order to provide eggs and infective larvae, respectively, for use in the egg hatch assay and larval motility assay systems. While the assays proved effective in quantifying drug sensitivity in larvae of the drug-susceptible hookworms examined in this study, their ability to indicate drug resistance in larval or adult hookworms remains to be determined.

Animals↗
PubMed1996

Adaptation to arid environment: Haemonchus longistipes in dromedaries of Saharo-Sahelian areas of Mauritania.

The adaptations of the trichostrongylid nematode Haemonchus longistipes of dromedaries (Camelus dromedarius) to the harsh environment of Saharo-Sahelian climate were assessed by means of (i) an epidemiological survey of dromedary infection in the south-west of Mauritania, (ii) an estimate over a 3 year period of parasite distribution within the host population and of prolificacy of H. longistipes females recovered from natural populations of infected dromedaries sampled at Nouakchott's slaughterhouse, and (iii) experimental infections of young dromedaries during three different periods of the year (end of the rainy season, middle and end of the dry season). Egg excretions (estimated by faecal egg counts), infective larvae derived from eggs as well as female prolificacy showed a marked seasonal pattern: high values in the rainy season and very low values in the dry season (especially March and April). Female prolificacy differed slightly between morphotypes: the knobbed type excreting over a longer period than the linguiform and smooth types. Following experimental infections in young dromedaries, arrest of larval development took place irrespective of the period. The survival strategy of H. longistipes in the dry season was based only on arrested larval development. Patent infections occurred from July to October, i.e. during the rainy season and was facilitated by the conjunction of high prevalence and intensity of adult worm burdens associated with high female prolificacy.

Adaptation, Physiological↗
PubMed2001

Histological study of the development of the embryo and early larva of Oreochromis niloticus (Pisces: Cichlidae).

The developmental stages of Oreochromis niloticus are similar to those described in other mouth-breeding tilapias except that, as in zebrafish, no cavity was found in the blastula. Variation in the rate of development of the embryo and larva of O. niloticus was found within a clutch of eggs as well as between clutches. Hatching glands are described for the first time in tilapias. They are widely distributed within the ectoderm covering the head, body, tail, and surface of the yolk sac near its attachment to the embryo. Timing of larval development is similar to that in other mouthbrooding tilapias, but is slower than that found in substrate-spawning tilapias. A pneumatic duct connects the swimbladder to the digestive tract and swimbladder inflation and initiation of feeding occurs at about the same time. The digestive tract of the larva 8 and 9 days after fertilization is similar to that found in the adult, except that there are no digestive glands. An endocrine pancreatic islet was first seen 76 h after fertilization. A prominent thymus gland is present at 100 h. Hematopoietic tissue develops in the vicinity of the pronephros during early larval development. A spleen develops later, 7 days after fertilization.

Animals↗
PubMed2001

Effect of sex steroids on gonadal differentiation and sex reversal in the frog, Rana curtipes.

The bicolored frog, Rana curtipes, is endemic to Western Ghats of Southern India, having a prolonged larval life. In this species, gonadal differentiation is of the semidifferentiated type. The gonads initially differentiate into ovaries in all the individuals at Gosner stage 25. Later, in genetic males, the oocytes degenerate and testicular differentiation occurs at stages 30-31. Exposure of R. curtipes tadpoles to 50 microg/L of testosterone (T) or estradiol-17beta (E(2)) during stages 24-26 or 29-32 did not affect gonadal sex differentiation and proportion of males and females at metamorphosis. In all the groups, the sex ratio was almost 1:1 as in the controls. Likewise, exposure of tadpoles to low concentration of steroids (12.5 microg/L T or E(2)) throughout larval development was ineffective in altering the sex ratio or the gonadal sex differentiation. On the other hand, exposure to higher concentrations of steroids (25 and 50 microg/L) throughout the larval development (stages 25-45) significantly skewed the sex ratio toward the male or female direction, depending upon the sex steroid used. Thus, exposure to T or E(2) throughout the larval period could produce 93% males or 79% females, respectively, indicating the ability of these steroids to cause sex reversal. This study shows a possible absence of a "critical stage" that is sensitive to sex steroids for gonadal sex reversal in this frog.

Animals↗
PubMed2002

Changes of protein tyrosine phosphorylation in third instar larval integument of the Mediterranean fruit fly, Ceratitis capitata.

Developmental analysis of the tyrosine protein phosphorylation levels in larval integument and partial characterization of the endogenous protein tyrosine kinase activity (PTK) in Ceratitis capitata are described in this study. Larval integument contains high levels of PTK activity at the early stages of the third instar, which progressively declines to low levels in the white pupal stage. An integumental 90-kDa polypeptide was identified to have prominent endogenous PTK activity and follow a similar developmental pattern. The major integumental phosphotyrosine-containing polypeptides have apparent molecular weights of 30, 41, 44, 46, and 54 kDa, respectively. Polypeptides with molecular weights of 62 and 73 kDa were identified as Ser/Thr-containing phosphoproteins and were shown to exhibit high levels of phosphorylation at the middle stage of larval development. These differences are likely to be due to the higher activation state of the protein tyrosine kinase(s) at the early stages of larval development.

Animals↗
PubMed2005

The effects of metals on embryo-larval and adult life stages of the sea urchin, Diadema antillarum.

Since the massive population decline of the long-spined sea urchin, Diadema antillarum, in the early 1980s, the dynamics of coral reef ecosystems in the Caribbean have changed tremendously. The absence of D. antillarum, once a keystone herbivore, has led to macroalgal dominance in many of these reef communities. D. antillarum is not only important ecologically, but may also be a sensitive bioindicator species for toxicant exposure. Echinoderm larval development tests were conducted with D. antillarum exposed to elevated levels of aqueous copper (Cu), silver (Ag), nickel (Ni), or selenium (Se). All metals significantly affected larval development, based on normal development to the pluteus stage. The EC50s based on dissolved metal concentrations were 11 microg/L Cu, 6 microg/L Ag, 15 microg/L Ni, and 26 microg/L Se. Adult sea urchins were exposed to aqueous copper under flow through conditions for 96 h. The 96-h LC50 for this exposure was 25 microg/L dissolved Cu. Additionally, behavioral and physiological disturbance was observed. The physiological responses included both acid-base balance disturbance, as evidenced by reduced coelomic fluid pH and apparent ionoregulatory effects. In addition, behavioral effects included spatial orientation within the exposure tank, spine closure, and loss of spines. The high sensitivity of both adult and larval D. antillarum to these metals supports the use of this organism as an important biological indicator for metal exposure in marine environments.

Acid-Base Equilibrium↗
PubMedDate not supplied

[Ecology of the tick, Dermacentor silvarum O1].

Results of the experiments have shown that the development of Dermacentor silvarum from egg to imago varied from 44 to 46 days at 28 C and redundant humidity and from 50 to 52 days at 25 degrees C. The thermic threshold of larval development lies within a range of 8.6 degrees C, that of nymphs-9.7 degrees C. A sum of effective temperatures required for larval development averaged 123.5 degrees C, for nymphs-225 degrees C and for the whole ontogenesis-from 570 to 690 degrees C. In the north of the distribution area of D. silvarum this species seems to occur only in those localities, where a sum of effective temperatures is higher than 10 C and makes not less than 570 degrees C.

Animals↗
PubMed2004

Determination of Vibrio scophthalmi and its phenotypic diversity in turbot larvae.

The association of Vibrio scophthalmi with turbot larvae was assessed, by molecular methods with a species-specific probe, in the rearing stages of turbot (Scophthalmus maximus) larvae using a routine batch of production at a fish farm. The phenotypic diversity of this bacterial species was also studied to identify predominant phenotypes at successive stages of larval development. Vibrio scophthalmi was detected in all turbot larvae samples except in the sample from day 0 after hatching. The percentage of V. scophthalmi in the intestinal microbiota increased throughout larval development. Vibrio scophthalmi was also detected in live food (brine shrimps) and water from the tanks, but not in the sediment. All turbot larvae, 15-57 day old, showed several V. scophthalmi phenotypes, and a pattern of successive waves of phenotypes was observed during successive larval stages. This indicates that certain strains may colonize the intestine more efficiently and thus maintain their population for longer than other strains. Vibrio scophthalmi populations from turbots of different origin were very similar, suggesting that irrespective of geographical area, turbot populations share similar V. scophthalmi strains. Vibrio scophthalmi strain was not isolated from other cultured fish, only turbot larvae, at the same hatchery receiving water from the same supply.

Animals↗
PubMed2005

Brominated flame retardants: activities in a crustacean development test and in an ecdysteroid screening assay.

Brominated flame retardants (BFRs) were investigated for toxic effects both in vivo and in vitro in two invertebrate bioassays. Subchronic effects of tetrabromobisphenol A (TBBPA), tribromophenol (TBP), and four polybrominated diphenyl ethers ([PBDEs]; BDE-28, BDE-47, BDE-99, and BDE-100) on larval development of the marine copepod Acartia tonsa were studied. For TBBPA and TBP 5-d effective median concentration (EC50) values for inhibition of the larval development rate were 125 and 810 microg/L, respectively, whereas the PBDEs were much more potent with 5-d EC50 in the low microg/L range (1.2 microg/L for BDE-100; 4.2 microg/L for BDE-99; 13 microg/L for BDE-28; and 13 microg/L for BDE-47). These concentrations were up to two orders of magnitude below the 48-h LC50 for acute adult toxicity (108 microg/L for BDE-28; 400 microg/L for TBBPA; 520 microg/L for BDE-100; 705 microg/L for BDE-99; 1,500 microg/L for TBP; and 2,370 microg/L for BDE-47). To distinguish between general toxicological and endocrine-mediated toxic effects, the BFRs were assessed in vitro for ecdysteroid agonistic/antagonistic activity with the ecdysteroid-responsive Drosophila melanogaster B(II)-cell line. The pentabrominated diphenyl ethers BDE-99 and BDE-100 showed weak ecdysteroid antagonistic activity. Thus, these PBDEs may be regarded as potential endocrine disrupters in invertebrates. The combination of in vitro assays and subchronic biotests with ecologically important crustacean species is a rapid and cost-effective tool when screening for sublethal effects of BFRs and other chemicals.

Animals↗
PubMed2002

Proteolytic cleavage of the developmentally important cadherin BT-R1 in the midgut epithelium of Manduca sexta.

BT-R1 (M(r) = 210 kDa) represents a new type of insect cadherin that is expressed specifically in the midgut epithelium during growth and development of Manduca sexta larvae. It also is a target receptor for the Cry1A toxins of the entomopathogenic bacterium Bacillus thuringiensis. Expression of BT-R1, which varies during larval development, correlates with the abundance of the protein and with the differential cleavage of the molecule at each developmental stage. The cleavage of BT-R1 is calcium dependent, and consequently, Ca2+ directly influences the structural integrity of BT-R1. Indeed, removal of calcium ions by chelating agents promotes cleavage of the BT-R1 ectodomain, resulting in formation of fragments that are similar to those observed during larval development. Partial purification of proteins from brush border membrane vesicles (BBMVs) by gel filtration chromatography hinders the cleavage of BT-R1 in the presence of EDTA and EGTA, indicating that there is specific proteolytic activity associated with the BBMV. This specific proteolytic cleavage of BT-R1 not only alters the integrity of BT-R1 but it most likely is implicated in cell adhesion events during differentiation and development of M. sexta midgut epithelium. We propose a model for calcium-dependent protection of BT-R1 as well as a cleavage pattern that may modulate the molecular interactions and adhesive properties of its ectodomain. Molecular characterization of such a protection mechanism should lead to a better understanding of how the function of specific cadherins is modulated during tissue differentiation and insect development.

Animals↗
PubMed2003

Developmental responses to predation risk in morphologically defended mayflies.

Densities and species composition of predators could affect morphological defences, larval development and the timing of emergence of their prey. To address this issue we studied the morphology and life history of an ephemerellid mayfly, Ephemerella invaria, from two streams in a deciduous forested drainage basin in central New York. Both streams contained predatory fish, but densities and species composition of fish differed. A field survey provided evidence that Ephemerella inhabiting a stream with > or =10 fish species and high relative densities of fish emerged several weeks earlier and at smaller sizes than Ephemerella inhabiting a nearby tributary with approximately 2 fish species and low relative densities of fish. However, the two populations of mayflies showed no differences in defensive morphology or growth rates. In laboratory rearing experiments, we exposed Ephemerella larvae from these two locations to fish chemical cues or control water (no fish) over 2 months to test whether differences in life histories could be attributed to fish. Fish cues induced faster larval development, but also smaller size of mature Ephemerella individuals from both high and low predator locations. Although shorter development times in more dangerous environments could increase larval survival, smaller size of females results in a fecundity cost associated with this life history shift. Consistent with the field studies, laboratory rearing experiments revealed no effects of fish cues on Ephemerella's morphological defences. These data suggest that variation in the density or species composition of predators may favour the evolution of developmental plasticity to reduce mortality in the larval environment.

Adaptation, Physiological↗
PubMed1994

Effects of a natural marsh fire on larval populations of Culex Salinarius in east Texas.

A natural marsh fire caused by lightning suppressed Culex salinarius larval populations for 2 months following the fire. Removal of emergent vegetation and higher water temperatures rendered burned-area pools unsuitable either for larval development or deposition of eggs or both. With a drop in seasonal ambient temperature and a regrowth of emergent vegetation, the burned areas returned to being suitable larval development sites for Culex salinarius. no differences in water salinity or pH were observed between burned and unburned locations.

Animals↗
PubMed2003

Role of DE-cadherin in neuroblast proliferation, neural morphogenesis, and axon tract formation in Drosophila larval brain development.

In the wild-type brain, the Drosophila classic cadherin DE-cadherin is expressed globally by postembryonic neuroblasts and their lineages ("secondary lineages"), as well as glial cells. To address the role of DE-cadherin in the larval brain, we took advantage of the dominant-negative DE-cad(ex) construct, the expression of which was directed to neurons, glial cells, or both. Global expression of DE-cad(ex) driven by a heat pulse during the early second instar resulted in a severe phenotype that included deficits in neural proliferation. Neuroblasts appeared in approximately normal numbers but had highly reduced mitotic activity. When the DE-cad(ex) construct was driven by the glial-specific driver gcm-Gal4, the effect of DE-cad(ex) on neuroblast proliferation could be replicated, which indicates that DE-cadherin acts in glial cells to promote proliferation of neuroblasts. Expression of DE-cad(ex) in neurons, cortex glia, or both results in abnormalities in cortex layering and in trajectories of secondary axons. In the wild-type brain, neuroblasts and neurons generated at different time points are arranged concentrically around the neuropile, with the DE-cadherin-positive neuroblasts and young secondary neurons at the surface, followed by older secondary neurons and primary neurons. Axons of secondary lineages follow a straight radial course toward the neuropile. Processes of glial cells located in the cortex form a scaffold, called trophospongium, that enwraps neuroblasts and neurons. Expression of DE-cad(ex) in neurons, cortex glia, or both disrupted the regular placement of neuroblasts and secondary neurons and resulted in abnormal trajectories of cell body fiber tracts. We conclude that DE-cadherin plays a pivotal role in larval brain proliferation, brain cortex morphogenesis, and axon growth.

Animals↗
PubMed1997

Mutation of the central nervous system neuroblast proliferation repressor ana leads to defects in larval olfactory behavior.

In the developing nervous system, interactions between glia and immature neurons or neuroblasts regulate axon pathfinding, migration, and cell division, and therefore affect structure and function. Glial control of neuroblast cell division has been documented by studies of the anachronism (ana) gene of Drosophila melanogaster. ana encodes a glycoprotein which, in the developing larval central nervous system, is secreted by glia that neighbor regulated neuroblasts. Mutations in ana lead to premature neuroblast proliferation in the larval brain. Examination of lacZ expression from an ana enhancer trap line as well as detection of the ana protein show that ana is also expressed in the larval antennal-maxillary complex (AMC) at all larval stages. As previously reported for the central nervous system, ana expression in the AMC appears to be confined to glial cells. Larval olfactory system function in ana mutants was assayed in a behavioral paradigm. When tested with the three different chemoattractants, third instar ana9 mutant larvae showed diminished olfactory response compared to controls. Examination of a second ana allele revealed aberrant olfactory response to ethyl acetate, demonstrating that more than one mutation in ana can give rise to abnormal larval olfactory behavior. Assays of early first instar ana9 mutant larvae revealed defective olfactory behavior, implying that the olfactory phenotype stems from early larval AMC and/or embryonic origins. This is consistent with proliferation analysis in the early larval AMC region which uncovered a significantly higher number of S-phase cells in ana9 mutants.

Alleles↗