Neuroendocrine control of moulting cycle in mealworms: Bioassay of moulting hormone

The moulting hormone content of mealworm homogenates was determined by injection of partially purified fractions into abdomens of mature larvae of Musca domestica. In mealworms with a 12-day interval between ecdyses, moulting hormone was at a maximum at 8 days.     

Structure of the toad epidermis during the moulting cycle

Summary Skin samples were taken from 17 toads (Bufo bufo) in various phases of the moulting cycle. The phase was determined by recording a number of moulting intervals prior to sacrifice and by study of the macroscopic appearance of the skin and the moulting behaviour at sacrifice. Eight of the toads were in the moult when the samples were taken.Characteristic morphological changes were found to be restricted to a period immediately prior to and after shedding of the slough. Chemical changes of the membranes of stratum corneum (or material adhered to them) were observed already prior to adoption of the moulting posture. The separation from the underlying epidermis prior to shedding was accompanied by a swelling of the stratum corneum cells. After final detachment of the slough the replacement layer was differentiated into a new stratum corneum within 24 hours. Significant changes in the morphology of the flask cells were not observed.The findings are discussed with emphasis on the processes of separation and differentiation of the stratum corneum. Based on the morphology of the epidermis the following terminology is proposed for the phases of the moulting cycle: Intermoult phase, preparation phase, early shedding phase, late shedding phase, and differentiation phase.The authors wish to thank professor C.B. Jørgensen, Dr. D. P. Knight and Dr. E.H. Larsen for valuable discussions. The technical assistance of Miss Susanne Binzer and Mrs. Grete Budtz is gratefully acknowledged. G.B. kept records of the moults. Without her patient and careful observations during several weeks it had not been possible to obtain the present material.     

Daphnia population growth but not moulting is a substantial phosphorus drain for phytoplankton

SUMMARY 1. Negative effects of zooplankton on the availability of phosphorus (P) for phytoplankton as a result of the retention of nutrients in zooplankton biomass and the sedimentation of exoskeletal remains after moulting, have been recently proposed. 2. In a mesocosm study, the relative importance of these mechanisms was tested for the freshwater cladoceran Daphnia hyalina×galeata. A total of 13 mesocosm bags was suspended in a mesotrophic German lake during summer 2000 and fertilised with inorganic P in order to obtain a total nitrogen to total P ratio closer to the Redfield ratio. D. hyalina×galeata was then added at a logarithmically scaled density gradient of up to 40 ind. L^?1. Zooplankton densities, dissolved inorganic, particulate organic (seston <100 μm), as well as total nutrient concentrations were monitored. Additionally, nutrient concentrations of sediment water removed from the bottom of the mesocosm bags via a manual pump were determined. 3. Seston carbon (C), seston P and total P were significantly negatively correlated with Daphnia densities. The amount of particulate P (～5–6 μg P L^?1) sequestered from the seston compartment by Daphnia corresponded roughly to the increase of zooplankton biomass (population growth). Soluble reactive phosphorous (SRP) was at all times high (～25–35 μg P L^?1) and possibly unavailable to phytoplankton as a result of P adsorption to calcite during a calcite precipitation event (whiting). P concentrations determined in sediment water were generally <60 μg P m^?2 and thus never exceeded 1% of the total amount of P bound in particulate matter of the overlying water column. 4. Seston C : P ratios followed a polynomial second‐order function: At Daphnia densities <40 ind. L^?1 a positive linear relationship was evident, which is explained by the stronger reduction of P compared with C in seston, and transfer of seston P to zooplankton. Highest seston C : P ratios of ～300 : 1 were observed at Daphnia densities of ～30–50 ind. L^?1, which is in agreement with proposed threshold values limiting Daphnia reproductive growth. At Daphnia densities >40–50 ind. L^?1 C : P ratios were decreased because of the strong reduction of seston C at close to constantly low seston P‐values of ～3–4 μg P L^?1. 5. At least for Daphnia, it may be concluded that – unlike population growth – the sedimentation of faecal pellets and carapaces after moulting seem negligible processes in pelagic phosphorus dynamics.     

Trophic interactions and population growth rates: describing patterns and identifying mechanisms

While the concept of population growth rate has been of central importance in the development of the theory of population dynamics, few empirical studies consider the intrinsic growth rate in detail, let alone how it may vary within and between populations of the same species. In an attempt to link theory with data we take two approaches. First, we address the question ''what growth rate patterns does theory predict we should see in time-series?'' The models make a number of predictions, which in general are supported by a comparative study between time-series of harvesting data from 352 red grouse populations. Variations in growth rate between grouse populations were associated with factors that reflected the quality and availability of the main food plant of the grouse. However, while these results support predictions from theory, they provide no clear insight into the mechanisms influencing reductions in population growth rate and regulation. In the second part of the paper, we consider the results of experiments, first at the individual level and then at the population level, to identify the important mechanisms influencing changes in individual productivity and population growth rate. The parasitic nematode Trichostrongylus tenuis is found to have an important influence on productivity, and when incorporated into models with their patterns of distribution between individuals has a destabilizing effect and generates negative growth rates. The hypothesis that negative growth rates at the population level were caused by parasites was demonstrated by a replicated population level experiment. With a sound and tested model framework we then explore the interaction with other natural enemies and show that in general they tend to stabilize variations in growth rate. Interestingly, the models show selective predators that remove heavily infected individuals can release the grouse from parasite-induced regulation and allow equilibrium populations to rise. By contrast, a tick-borne virus that killed chicks simply leads to a reduction in the equilibrium. When humans take grouse they do not appear to stabilize populations and this may be because many of the infective stages are available for infection before harvesting commences. In our opinion, an understanding of growth rates and population dynamics is best achieved through a mechanistic approach that includes a sound experimental approach with the development of models. Models can be tested further to explore how the community of predators and others interact with their prey.     

Breeding and moulting locations and migration patterns of the Atlantic population of Steller's eiders Polysticta stelleri as determined from satellite telemetry

This study was designed to determine the spring, summer, autumn, and early winter distribution, migration routes, and timing of migration of the Atlantic population of Steller's eiders Polysticta stelleri . Satellite transmitters were implanted in 20 eiders captured in April 2001 at Vadsø, Norway, and their locations were determined from 5 May 2001 to 6 February 2002. Regions where birds concentrated from spring until returning to wintering areas included coastal waters from western Finnmark, Norway, to the eastern Taymyr Peninsula, Russia. Novaya Zemlya, Russia, particularly the Mollera Bay region, was used extensively during spring staging, moult, and autumn staging; regions of the Kola, Kanin, and Gydanskiy peninsulas, Russia, were used extensively during spring and moult migrations. Steller's eiders migrated across the Barents and Kara seas and along the Kara Sea and Kola Peninsula coastal waters to nesting, moulting, and wintering areas. The majority of marked eiders (9 of 15) were flightless in near-shore waters along the west side of Novaya Zemlya. Eiders were also flightless in northern Norway and along the Kanin and at Kola Peninsula coasts. We compare and contrast natural history characteristics of the Atlantic and Pacific populations and discuss evolutionary and ecological factors influencing their distribution.     

Breeding and moulting locations and migration patterns of the Atlantic population of Steller's eiders Polysticta stelleri as determined from satellite telemetry

This study was designed to determine the spring, summer, autumn, and early winter distribution, migration routes, and timing of migration of the Atlantic population of Steller's eiders Polysticta stelleri. Satellite transmitters were implanted in 20 eiders captured in April 2001 at Vadsø, Norway, and their locations were determined from 5 May 2001 to 6 February 2002. Regions where birds concentrated from spring until returning to wintering areas included coastal waters from western Finnmark, Norway, to the eastern Taymyr Peninsula, Russia. Novaya Zemlya, Russia, particularly the Mollera Bay region, was used extensively during spring staging, moult, and autumn staging; regions of the Kola, Kanin, and Gydanskiy peninsulas, Russia, were used extensively during spring and moult migrations. Steller's eiders migrated across the Barents and Kara seas and along the Kara Sea and Kola Peninsula coastal waters to nesting, moulting, and wintering areas. The majority of marked eiders (9 of 15) were flightless in near‐shore waters along the west side of Novaya Zemlya. Eiders were also flightless in northern Norway and along the Kanin and at Kola Peninsula coasts. We compare and contrast natural history characteristics of the Atlantic and Pacific populations and discuss evolutionary and ecological factors influencing their distribution.     

Determinants and patterns of population growth in water hyacinth

Mathematical models of the growth of water hyacinth are developed to provide a sound basis for assessing existing and potential control options. We show that under constant experimental conditions, water hyacinth shows logistic growth (r² of 0.69–1.00). The effects of nutrients and temperature on model parameters are explored using data from the literature. The model is verified against growth in a natural infestation. The resulting model incorporates two of the most important factors (temperature and water nutrient level) that determine whether water hyacinth is an important environmental problem at a given site. These relationships form a robust basis for further model development, and can be readily used to evaluate how the plant will respond to changes in nutrient inputs.     

Lipid metabolism of the female crab Pachygrapsus marmoratus during the moulting cycle

The moult induces important variations in the concentration and fatty acids composition of lipid classes during the moulting cycle of the female crab Pachygrapsus marmoratus regardless of the maturational degree of ovaries. Sexual maturity is characterized by a rise in lipids. Juveniles contain high levels of polyunsaturated fatty acids except in the ovary, whereas adults are composed mainly of monoethylenic acids. The moulting decrease of saturated fatty acids shows their importance during this crucial period, owing to their utilization as energy sources at the time of ecdysis. The late premoult fall of hepatopancreatic lipids results at once from inanition during the period before the exuviation and transfer of lipids through the hemolymph to the periphery in order to realize numerous changes occurring during the moulting process. The relative stability of lipid composition of ovaries in sexual pause during the moulting cycle agrees with a reduced metabolism of ovarian cells.     

Neuroendocrine control of moulting cycle in mealworms: Histology and autoradiography of cephalic components

Fluctuations in the activities of the cephalic neuroendocrine system of larval mealworms (Tenebrio molitor) have been investigated by autoradiographic and histological techniques. Shortly after ecdysis, the proteinaceous granules in the cytoplasm of the ‘A’ type medial neurosecretory cells of the brain undergo a marked increase in numbers per cell and in chromophilia; both numbers and stain density reach a maximum about two-thirds of the way through interval between ecdyses and then both decline precipitously. The cyclic histological changes are nicely correlated with overall patterns of protein synthesis, as demonstrated by incorporation of ³H-amino acids into the medial cells. Paradoxically no cyclicity was observed downstream: no fluctuations in numbers or chromophilia of stainable inclusions were detected in the axons of the medial neurosecretory cells, in the corresponding efferent nerves to the corpora cardiaca, or within the cardiaca themselves. Mechanisms are proposed to account for this apparent paradox, and the patterns of protein synthesis within the ‘A’ type medial neurosecretory cells are correlated with previously determined fluctuations in moulting hormone activity.     

Altitude and growth: a study of the patterns of physical growth of a high altitude Peruvian Quechua population

Data on physical growth were obtained for a sample of 1202 Quechua subjects, aged 2 to 35 years from the district of Nuñoa, Puno, located in the southern highlands (altitude 4000–5500m) of Peru. These data were supplemented by a three-year longitudinal study of 300 subjects, aged 1 to 22 years. The patterns of physical growth of members of the indigenous population of Nuñoa are characterized by (1) late sexual dimorphism, (2) slow and prolonged growth in body size, (3) late and poorly defined adolescent stature spurt in both males and females, and (4) accelerated development in chest size. The socio-economic factors associated with urban-rural and altitude differences appear to be reflected in greater deposition of subcutaneous fat and increased weight but do not seem to influence the development of stature. We suggest the pattern of growth of this population is related to the hypoxic effects of high altitude, and/or reflects a genetic adaptation to such stress. The anthropometric and physiological studies conducted during this and previous studies and the comparative data from Peruvian populations situated at lower altitudes document the specific adaptive response of the chest wall to the hypoxic effects of high altitude.     

Impacts of population growth and economic development on the nitrogen cycle in Asia

Asia is the major consumer of fertilizer nitrogen and energy in the world, and consequently shares a considerable proportion of the world creation of reactive nitrogen (Nr). However, if estimated on per capita basis, Asia is characterized by a lower arable land area, fertilizer nitrogen consumption, energy consumption, and gross domestic product, as well as lower daily protein intake. To meet the increasing needs for food and energy for the growing population combined with the improvement of living standards, Nr will inevitably increase. The present study estimates the creation of Nr and the emissions of various N compounds into environment in Asia currently and in 2030. In comparison with the world averages, the lower fertilizer nitrogen and energy use efficiencies, and the lower use of animal wastes for agriculture imply that there is potential for moderating the increase in Nr and its impacts on the environment. Strategies for moderating the increase are discussed.     

Impacts of population growth and economic development on the nitrogen cycle in Asia

Asia is the major consumer of fertilizer nitrogen and energy in the world, and consequently shares a considerable proportion of the world creation of reactive nitrogen (Nr). However, if estimated on per capita basis, Asia is characterized by a lower arable land area, fertilizer nitrogen consumption, energy consumption, and gross domestic product, as well as lower daily protein intake. To meet the increasing needs for food and energy for the growing population combined with the improvement of living standards, Nr will inevitably increase. The present study estimates the creation of Nr and the emissions of various N compounds into environment in Asia currently and in 2030. In comparison with the world averages, the lower fertilizer nitrogen and energy use efficiencies, and the lower use of animal wastes for agriculture imply that there is potential for moderating the increase in Nr and its impacts on the environment. Strategies for moderating the increase are discussed.     

Impacts of population growth and economic development on the nitrogen cycle in Asia

Asia is the major consumer of fertilizer nitrogen and energy in the world, and consequently shares a considerable proportion of the world creation of reactive nitrogen (Nr). However, if estimated on per capita basis, Asia is characterized by a lower arable land area, fertilizer nitrogen consumption, energy consumption, and gross domestic product, as well as lower daily protein intake. To meet the increasing needs for food and energy for the growing population combined with the improvement of living standards, Nr will inevitably increase. The present study estimates the creation of Nr and the emissions of various N compounds into environment in Asia currently and in 2030. In comparison with the world averages, the lower fertilizer nitrogen and energy use efficiencies, and the lower use of animal wastes for agriculture imply that there is potential for moderating the increase in Nr and its impacts on the environment. Strategies for moderating the increase are discussed.     

Bursicon and the metabolism of tyrosine in the moulting cycle of Pieris larvae

In fourth instar larvae of Pieris brassicae the haemolymph tyrosine level begins to rise about 1 day before apolysis to reach a level about treble that in the middle of the instar. Between apolysis and ecdysis the haemolymph tyrosine level appears to decline, until just before ecdysis another steep rise occurs. About 30 min after ecdysis a steep decline starts, levelling off gradually until the level in the middle of the instar is restored.Bursicon assays show that this hormone operates in the haemolymph both during apolysis and after ecdysis; but during the actual ecdysis no bursicon activity can be demonstrated in the haemolymph.Indications have been found that the bursicon activity can restore itself spontaneously in the haemolymph of newly ecdysed larvae. This would suggest that during ecdysis a bursicon inhibitor of restricted life is operating.     

Azadirachtin: its effect on gut motility, growth and moulting in Locusta

ABSTRACT. The biological effect of azadirachtin on fifth instar nymphs of Locusta migratoria migratorioides (R & F) have been studied in detail. Azadirachtin injection at the beginning of the instar results in a dose-dependent range of developmental aberrations. Low concentrations ( c. 1.7/μg/g body weight) result in adults with curled wing tips and reduced longevity; higher concentrations ( c. 2.9μg/g) result in death during the imaginal moult; doses of c. 6.5μg/g cause death immediately prior to the moult; and doses of c. 7.3μg/g induce a greatly extended instar. Such doses are related to a proportionately slower growth rate of the insect and a significantly reduced food intake, as assessed by wet weight and faeces production. Doses of 80μg/g result in death within 24 h. Experiments in vivo and in vitro demonstrate a significant reduction with azadirachtin treatment in the rate of passage of food through the gut, and in gut motility. The significance of this direct effect on gut motility is discussed in relation to the mode of action of azadirachtin on growth and moulting.     

Changes in apparent water permeability during the moulting cycle in the western rock lobster

The kinetics of water exchange, as measured by ³H₂O fluxes, were examined in the western rock lobster, Panulirus longipes (Milne Edwards) during stages C₄, D₃, D₄, D₄-E and B₁ of the moulting cycle. A series of samples of blood and external water was taken during each experiment and the inward and outward rate constants found using the SAAM 25 computer program, assuming a simple 2-compartment model with reversible exchange. Both inward and outward turnover rates remained constant up to the swelling prior to ecdysis when there was an increase of 203% inwards compared with 133% outwards. The latter increased in stage B₁, so that both rates were comparably high, probably due to the increased permeability of the soft integument.Further analysis showed that the rock lobster does not behave as a single compartment with respect to tritiated water. Two compartments were resolved by graphical analysis, one with fast and the other with slow exchange. It is suggested that blood and tissue ‘free’ water comprise one compartment and chemically ‘bound’ water the other, with fast exchange between the free and bound water and relatively slow exchange between free body water and the external medium.     

Lipid metabolism of the male crab Pachygrapsus marmoratus during the moulting cycle

The moult induces important variations in the concentrations and fatty acid composition of lipid classes during the moulting cycle of the male crab Pachygrapsus marmoratus. Phospholipids are the predominant lipid class. The high levels in total saturated fatty acids but also in oleic and palmitic acids result of the semi-terrestrial ethology of this grapsidae. The hepatopancreas presents the most notable variations in the lipid concentration during the moulting cycle. Transport of hepatopancreatic lipids through the hemolymph to the periphery occurs during the end of premolt, just before the new tissues constitution.     

Spatio-temporal leaf growth patterns of Arabidopsis thaliana and evidence for sugar control of the diel leaf growth cycle

Leaf growth dynamics are driven by diel rhythms. The analysis of spatio-temporal leaf growth patterns in Arabidopsis thaliana wild type and mutants of interest is a promising approach to elucidate molecular mechanisms controlling growth. The diel availability of carbohydrates is thought to affect diel growth. A digital image sequence processing (DISP)-based noninvasive technique for visualizing and quantifying highly resolved spatio-temporal leaf growth was adapted for the model plant A. thaliana. Diel growth patterns were analysed for the wild type and for a mutant with altered diel carbohydrate metabolism. A. thaliana leaves showed highest relative growth rates (RGRs) at dawn and lowest RGRs at the beginning of the night. Along the lamina, a clear basipetal gradient of growth rate distribution was found, similar to that in many other dicotyledonous species. The starch-free 1 (stf1) mutant revealed changed temporal growth patterns with reduced nocturnal, and increased afternoon, growth activity. The established DISP technique is presented as a valuable tool to detect altered temporal growth patterns in A. thaliana mutants. Endogenous changes in the diel carbohydrate availability of the starch-free mutant clearly affected its diel growth rhythms.