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PubMed1998

Genetic analysis of Drosophila larval optic nerve development.

To identify genes necessary for establishing connections in the Drosophila sensory nervous system, we designed a screen for mutations affecting development of the larval visual system. The larval visual system has a simple and stereotypic morphology, can be recognized histologically by a variety of techniques, and is unnecessary for viability. Therefore, it provides an opportunity to identify genes involved in all stages of development of a simple, specific neuronal connection. By direct observation of the larval visual system in mutant embryos, we identified 24 mutations affecting its development; 13 of these are larval visual system-specific. These 13 mutations can be grouped phenotypically into five classes based on their effects on location, path or morphology of the larval visual system nerves and organs. These mutants and phenotypic classifications provide a context for further analysis of neuronal development, pathfinding and target recognition.

Animals↗

PubMed2006

Statistical estimation of degree days of mosquito development under fluctuating temperatures in the field.

Degree-days are important parameters for developing predictive models of mosquito populations. Conventional methods of estimation of degree-days are typically applied to observations under constant temperatures in the laboratory. These methods are difficult to apply in the field where temperatures fluctuate. For estimating degree-days of larval developments of mosquitoes in the field, we applied Dennis' stochastic phenological model to a semi-field observation of Culex restuans. A parametric bootstrap approach was introduced to estimate standard errors of the parameters. We found that the estimated degree-days varied with various assumptions about the temperature base. Given the latter, the model can satisfactorily estimate the degree-days of larval and pupal developments of Cx. resturans. This approach is especially useful to measure spatio-temporal variability in larval development among various types of aquatic habitats.

Animals↗

PubMed1978

Development of the compound eyes of dragonflies (Odonata). II. Development of the larval compound eyes.

The development of the compound eye was analyzed by marking individual ommatidia and by studying naturally occurring pigment band patterns. New ommatidia are added to the eye along its anterior margin. This changes the directions of view of the older ommatidia with the greatest change occurring in the fovea. New ommatidia are added to the fovea medially, and old ones are removed laterally as their interommatidial angles and directions of view in the visual field change. Over one-third of the aeshnid ommatidia are foveal during at least one of the early larval instars, and are then used for peripheral vision later in development. The design of each ommatidium is a compromise so that it is adapted for all stages of development, but sometimes better adapted for one instar than for others. Factors which are balanced for best vision are lens diameter, facet admission function, interommatidial angle, and inclination of the optic axis to the eye surface. Ommatidia are described in terms of these factors throughout their life history, from initial differentiation anteriorly, through passage through the fovea, to their final relatively posterior location.

Animals↗

PubMed1999

Larva-adult relationships in an ancestral dipteran: A re-examination of sensillar pathways across the antenna and leg anlagen of Chaoborus crystallinus (DeGeer, 1776; Chaoboridae).

In one of his classical studies on insect metamorphosis, Weismann compared the imaginal anlagen of the ancestral phantom midge, Chaoborus, with those of advanced brachycerans. We have expanded his findings on the relationships between larval and imaginal organs using electron microscopy and cobalt backfilling of the antenna and leg anlagen and the axonal trajectories of corresponding larval sensilla. We show that both primordia are confluent with the larval antennae and "leg" sensilla (an ancestral Keilin organ), respectively. These fully developed larval organs represent the distal tips of the imaginal anlagen rather than separate cell clusters. The axons of the larval antenna and leg sensilla project across the corresponding anlagen to their target neuromeres within the central nervous system (CNS). Within the discs, nerves composed of these larval axons, developing afferent fibres and efferences ascending from the CNS are found. Both the structure of the primordia and the axonal trajectories thus relate the situation found in advanced brachycerans with that seen in more ancestral insects. In addition, the larval antennae, legs, wings and even the eyes possess very similar afferent pioneer trajectories supporting the idea that the described pattern is generally used in the ontogeny of sensory systems.

Animals↗

PubMed1998

Expression pattern of a butterfly achaete-scute homolog reveals the homology of butterfly wing scales and insect sensory bristles.

BACKGROUND: Lepidopteran wing scales are the individual units of wing color patterns and were a key innovation during Lepidopteran evolution. On the basis of developmental and morphological evidence, it has been proposed that the sensory bristles of the insect peripheral nervous system and the wing scales of Lepidoptera are homologous structures. In order to determine if the developmental pathways leading to Drosophila sensory bristle and butterfly scale formation use similar genetic circuitry, we cloned, from the butterfly Precis coenia, a homolog of the Drosophila achaete-scute (AS-C) genes--which encode transcription factors that promote neural precursor formation--and examined its expression pattern during development. RESULTS: During embryonic and larval development, the expression pattern of the AS-C homolog, ASH1, forecasted neural precursor formation. ASH1 was expressed both in embryonic proneural clusters--within which an individual cell retained ASH1 expression, enlarged, segregated, and became a neural precursor--and in larval wing discs in putative sensory mother cells. ASH1 was also expressed in pupal wings, however, in evenly spaced rows of enlarged cells that had segregated from the underlying epidermis but, rather than give rise to neural structures, each cell contributed to an individual scale. CONCLUSIONS: ASH1 appears to perform multiple functions throughout butterfly development, apparently promoting the initial events of selection and formation of both neural and scale precursor cells. The similarity in the cellular and molecular processes of scale and neural precursor formation suggests that the spatial regulation of an AS-C gene was modified during Lepidopteran evolution to promote scale cell formation.

Amino Acid Sequence↗

PubMed2001

Umingmakstrongylus pallikuukensis (Nematoda: Protostrongylidae) in gastropods: larval morphology, morphometrics, and development rates.

Morphological and morphometric aspects of larval development of Umingmakstrongylus pallikuukensis in Deroceras laeve and the effects of temperature on development rates in D. laeve and Deroceras reticulatum were investigated in the laboratory. Larval stages were best differentiated by separation of cuticular sheaths, tail structure, and viability following digestion. Growth in body and esophagus width was observed during the first-stage within the intermediate host, but the major increases in body length and width occurred immediately following the second molt. Larval development in D. laeve and D. reticulatum occurred more rapidly at warmer temperatures. The calculated threshold temperatures were 8.5 and 9.5 C in D. laeve and D. reticulatum, respectively, and 167 degree-days were required for development to third-stage larvae (L3) in both hosts. These thresholds are higher than those calculated from published data for the closely related Muellerius capillaris (4.2 C) but are similar to those for the more distantly related northern protostrongylid, Elaphostrongylus rangiferi (8.3-10.3 C). Conversely, degree-days required for development to infective L3 were more similar among the Muelleriinae than between this group and the Elaphostrongylinae. Developmental parameters for protostrongylid larvae may be influenced both by the environment and by features of the parasites and the intermediate hosts, including phylogeny.

Animals↗

PubMed2003

Early development of the Drosophila brain: III. The pattern of neuropile founder tracts during the larval period.

The Drosophila N-CAM homolog Fasciclin II (FasII) is expressed during the embryonic period in a subset of central neurons that pioneer the neuropile of the larval brain. Toward the end of embryogenesis, FasII expression in axon tracts diminishes but resumes from the late first larval instar in an increasingly complex pattern of axon tracts that join the tracts laid down in the embryo. We present evidence that FasII is expressed in a major fraction of the long axon tracts that interconnect different domains of the larval brain. For many tracts, FasII expression remains stable throughout larval development and pupal development. Therefore, the FasII pattern of axon tracts, along with the mushroom body and optic lobe, both of which are also FasII-positive, represents a useful set of landmarks that define different regions in the Drosophila brain throughout development. In this study, serial confocal brain sections were used to generate digital three-dimensional models of larval axon tracts at different stages. These models form part of our effort to generate an anatomic framework of Drosophila larval brain structure required for accurate localization of gene expression and gene function in experimental studies of neural development.

Animals↗

PubMed1995

Coulometric measurement of oxygen consumption during development of marine invertebrate embryos and larvae

Determining the metabolic rate of larval invertebrates from aquatic habitats is complicated by the problems of small size and the scarcity of suitable measurement techniques. In this study, coulometric respirometry (a new technique for the study of marine embryos and larvae) was used to explore several issues associated with the rate of energy use during embryonic and larval development of marine invertebrates from three phyla. Coulometric respirometry measures rates of oxygen consumption under normoxic conditions by electrochemically replacing the oxygen consumed by organisms during an experiment. This technique is based on the assumption that all electrons consumed by the anodic reactions result in the production of oxygen. We verify this assumption using direct measurements of oxygen production and show that the technique is sensitive enough (1 nmol O2 h-1) to quantify the oxygen consumption of a single individual swimming freely in a relatively large volume (2 ml). Continuous measurements can span days, and embryos in the coulometric respiration chambers develop to the larval stage at normal rates of differentiation. Measurements of metabolic rates were made with the coulometric respirometer during the complete life-span of larvae of three species (asteroid, Asterina miniata; bivalve, Crassostrea gigas; echinoid, Dendraster excentricus). For these species, metabolic power equations had mass exponents near unity (0.91.1), showing that metabolic rate scales isometrically with mass during larval growth. Metabolic rates were independent of the concentration of larvae used in the respirometer chambers for a range of larval concentrations from 4 to 400 larvae ml-1 (coulometric respirometer) and from 241 to 809 larvae ml-1 (polarographic oxygen sensor). Metabolic rates were measured using coulometric respirometry and two other commonly used techniques, polarographic oxygen sensors and Winkler's titration. Polarographic oxygen sensors in small, sealed chambers (100 µl) consistently gave the lowest values (by as much as 80 %) for the asteroid, echinoid and molluscan larvae. By comparison, rates of oxygen consumption measured using coulometric respirometry and Winkler's titration (to measure the change in oxygen concentration over time) were similar and consistently higher. Although the polarographic oxygen sensor is the most widely used method for measuring the metabolism of small animals in sealed 1001000 µl chambers, it appears that the metabolism of some larvae is adversely affected by the conditions within these respirometers.

Journal Article↗

PubMed1996

Juvenile hormone regulation and developmental expression of a Tenebrio desiccation stress protein gene.

Levels of a 28 kDa hemolymph protein, desiccation stress protein (dsp28), in the mealworm beetle, Tenebrio molitor, increase in response to desiccation and cold stress and are also developmentally regulated under nonstress conditions. Dsp28 mRNA is produced in the fat body, and its abundance changes dramatically throughout development. Transcript abundance increases throughout larval development, drops at pupation, and increases again in adults, the highest levels being found in females. The juvenile hormone (JH) analogue, methoprene, increased dsp28 transcript accumulation in pupae, suggesting that changing JH titres have a role in developmental expression and also perhaps contribute to dsp28 regulation during conditions of environmental stress. Genomic DNA, containing the entire dsp28 coding region plus 1.3 kb of upstream sequence, was isolated and potential regulatory sequences, including putative JH response elements, were identified.

Amino Acid Sequence↗

PubMed1991

The regulation of the cell cycle during Drosophila embryogenesis: the transition to polyteny.

The process of polytenization plays a crucial role in Drosophila development, and most of the larval tissues are polytene. By analyzing the pattern of DNA replication in embryos pulse-labeled with BrdU, we show that many larval tissues undergo a transition to begin becoming polytene late in embryogenesis. Our results demonstrate that in these larval tissues polyteny results from a modified cell cycle, the endo cell cycle, in which there is only an S (synthesis) phase and a G (gap) phase. A key regulator of the mitotic cell cycle, the product of the string gene (the Drosophila homologue of cdc25), is not required for the endo cell cycle. The developmental regulation of the endo cell cycle is striking in that tissue-specific domains undergo polytene DNA replication in a dynamic pattern at defined times in embryogenesis. During subsequent rounds of the endo cell cycle in late embryogenesis and first instar larval development, the domains are subdivided and the temporal control is not as rigid. The length of the G phase varies among different tissues. By quantifying DNA content, we show that during the early polytene S phases the genome is not fully duplicated.

Animals↗

PubMedDate not supplied

[Bionomical aspects of the Squamatoides triviattus (Diptera, Sarcophagidae) under laboratory conditions].

Experiments with Squamatoides trivitattus were carried out in two different controlled temperatures (16 +/- 1 degree C/50-60% RH and 27 +/- 1 degree C/70-80% RH). The viability of larvae and pupae at 27 degrees C was 89.82% and 92.75% respectively. Larvae did not develop at 16 degrees C. Larval development lasted for 20 +/- 4 hr, 16 +/- 8 hr and 60 +/- 7 hr for the first, second and third instars, respectively, completing a total of 96 +/- 6 hr. The mean pupal period lasted for 15.7 +/- 1.6 days. In longevity tables for the adults, life-expectancy for 50% of the colony submitted to 16 degrees C was of 1.78 weeks for males and 2.42 for females. At 27 degrees C a life-expectancy of 1.15 weeks for males and 0.78 week for females was recorded. The average life-spans for males and females at 16 degrees C were 3.5 +/- 2.0 and 3.8 +/- 2.6 weeks, respectively, and 1.9 +/- 1.2 weeks for both sexes. At 27 degrees C, the longevity recorded was of 2.1 +/- 1.3 weeks for males and 1.7 +/- 1.1 week for females.

Animals↗

PubMed1982

Effects of temperature on development of Onchocerca volvulus in Simulium ochraceum, and longevity of the simuliid vector.

The effects of temperature on the development of Onchocerca volvulus in Simulium ochraceum, and on the vector's longevity were studied under simulated environmental conditions in the laboratory. When S. ochraceum (which had fed on a person infected with O. volvulus) were maintained at different, constant temperatures (10-30 C), larvae developed to the infective stage between 20 and 28 C. The time required for development to the infective stage depended on the relationship of y = -0.3760 + 0.0222x (y = velocity in development; x = rearing temperature). However, larval development to the infective stage occurred in all groups kept at different temperatures by day and by night (25 C during the day and 10-18 C during the night), although the developmental period was prolonged (10 days in the group held at 25/18 C, and 13 days in other groups). The percentage of females harboring infective larva(e) among those maintained was highest at a constant temperature of 22 C (21.9%), followed by 15.0% at 25 C. When S. ochraceum females were held at day/night differing temperatures, much higher rates were observed at 25/16 C (30.0%) and at 25/14 C (23.0%). Our results suggest that the distribution of onchocerciasis in Guatemala may be related to ambient temperature and to day/night temperature cycles.

Animals↗

PubMed1997

Establishment of a free-mating colony of Anopheles albitarsis from Brazil.

The establishment of a free-mating colony of Anopheles albitarsis sensu siricto, a member of the Anopheles albitarsis complex, is described. Groups of females from the F5, F6, and F11 generations were examined, and the percent inseminated, mean number of eggs oviposited, and percent hatch discussed. The colony has been continued through 18 generations, with larval development averaging 10 days, and larval mortality ranging between 20 and 30%.

Animals↗

PubMed1992

The development and mortality of the free-living stages of Haemonchus contortus in laboratory culture.

Haemonchus contortus eggs were cultured in intact fecal pellets at various temperatures (5-35 degrees C) for 22 days. Temperature and relative humidity were kept constant throughout the incubation period. Nl larval development occurred at 5 degrees C; peak third-stage larval recovery occurred at 20 degrees C. Egg mortality was an age-dependent phenomenon, whereas larval mortality remained constant irrespective of larval age. Development was characterized by a minimum development time followed by a transition to the next stage which occurred at a constant rate. All rates were temperature dependent. The minimum development times reported here are much less than those previously reported. Based on these results a mathematical model was used to describe the demography of the free-living stages of H. contortus at various temperatures.

Animals↗

PubMed1984

Arresting development arrests aging in the nematode Caenorhabditis elegans.

Larval development of the nematode, Caenorhabditis elegans, can be arrested by either of two different treatment: (1) complete starvation, or (2) growth in a partially defined culture medium (axenic medium) of strains adapted to bacterial growth. The developmental arrest is complete under total starvation and the starved populations live about 10 days. The developmental block is incomplete in axenic medium; most animals mature but maturation takes 10 times longer than normal. If developmentally arrested cultures are returned to growth on E. coli, both the completely starved and the axenically arrested cultures mature at normal rates. Life-span is prolonged by 1 day for each day of complete starvation; life-span is prolonged by 0.7 days for each day of axenic arrest. These results suggest that aging and development are closely coupled in this system. The results are discussed in terms of previous observations on nutritional deprivation in other invertebrates and caloric restriction in mammals and are interpreted in light of theoretical models of senescence.

Aging↗

PubMed1988

Stress, altered energy availability and larval fitness in Drosophila melanogaster.

This paper reports some effects of temperature variation, nutritional stress and a novel alteration in energy availability upon larval fitness in Drosophila melanogaster. The cofactor nicotinamide adenine dinucleotide (NAD) has been chosen as a novel energy source to be supplemented in food during larval development. The effects have been assessed at the phenotypic level for larval survival and development time and at the genotypic level for the alcohol dehydrogenase (Adh) and glycerol-3-phosphate dehydrogenase (Gpdh) loci. Supplemented NAD was found to increase survival at the lower temperatures and decrease survival at the higher temperatures. Further, for each temperature, NAD decreased development time although this effect diminished as temperature increased. There were no significant effects at the genotypic level. Hence a phenotypic approach studying the effects of environmental stresses and novel energy availability may be useful in understanding fitness variation in Drosophila populations.

Animals↗

PubMed1986

Adipose tissue of Drosophila melanogaster: VII. Distribution of nuclear DNA amounts along the anterior-posterior axis in the larval fat body.

The DNA content of fat body nuclei was measured cytophotometrically as a function of position along an anterior-posterior (A-P) axis of the tissue throughout larval development. There was a dramatic 55-fold increase in the average amount of DNA per nucleus during the first 3 days of this period, but there was no further increase during the final day. However, the rate of increase had regional specificity. The amount of DNA per nucleus correlated significantly with its position along the A-P axis of the tissue: nuclei in a posterior direction contain gradually increasing amounts of DNA. There was up to a seven-fold difference between the smallest anterior and largest posterior nucleus. In addition, for three of the ages studied there was a subgradient in the posterior region with a slope that was considerably steeper than that of the overall tissue gradient. The tissue has three characteristic morphological regions, anterior, medial, and posterior, which can be recognized early in development and which are maintained throughout the larval period. The distribution of nuclear DNA classes determined for cells in each region for the final 2 days of larval life became fixed before the final day of development. The significance of the DNA gradient in terms of a protein storage gradient is discussed.

Adipose Tissue↗

PubMed2003

Two divergent slit1 genes in zebrafish.

Members of the Slit family regulate axon guidance and cell migration. To date, three vertebrate slit1 genes have been identified in mammals and orthologs of two, slit2 and slit3, have been identified in zebrafish. Here, we describe the cloning of full-length cDNAs for two zebrafish slit orthologs, slit1a and slit1b. Both predicted proteins contain the conserved motifs that characterize other vertebrate Slits. slit1a and slit1b are both expressed in the midline, hypochord, telencephalon, and hindbrain. Apart from these shared expression domains, however, their expression patterns largely differ. Whereas slit1a is expressed broadly in the central nervous system (CNS) and in the somites, pectoral fin buds, tail bud, and caudal fin folds, slit1b is expressed in the olfactory system throughout embryonic and larval development, and in the retina during larval stages. Their expression patterns, particularly that of slit1a, suggest that Slit proteins may have roles in tissue morphogenesis in addition to their established roles in axon guidance and cell migration.

Amino Acid Sequence↗