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31.
The steroid hormone ecdysone regulates the major post-embryonictransitions during the Drosophila life cycle, including theonset of, and progression through, metamorphosis. Reviewed hereare several recent studies that together give insight into boththe transduction of the ecdysone signal itself as well as otherpossible hormonal signaling events associated with metamorphosis.Genetic studies of the two components of the ecdysone receptor,EcR and usp, demonstrate that they are essential for the initiationof metamorphosis in Drosophila. These genes are not, however,required for some earlier events that prepare the animal formetamorphosis. Instead, the orphan nuclear receptor DHR78 appearsto regulate these events, possibly in response to an as yetunidentified hormone. An additional role for usp, independentfrom EcR function, has also been uncovered in epidermis andcuticle development, suggesting a possible role for usp in integratingecdysone and juvenile hormone signals. 相似文献
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1. Climate change has affected zooplankton phenology and abundance in many freshwater ecosystems. The strong temperature anomalies that characterise summer heat waves make these events particularly suitable to study the effects of different seasonal warming patterns on zooplankton. Since heat waves are expected to occur more frequently under continuing climate change, they may also allow us to investigate how freshwater systems will be affected in the future. 2. Using a long‐term data set (1991–2007) from a shallow, eutrophic lake in Germany, we identify time periods in spring and summer during which cyclopoid copepods and bosminids are particularly sensitive to changes in water temperature. Based on this knowledge, we consider why summer populations responded differently to recent heat wave events that occurred at different times in the season. 3. Linear regressions of moving averages suggested that water temperatures shortly before and shortly after the clear‐water phase (CWP) were crucial for summer development of bosminids and cyclopoid copepods, respectively. Algal food availability (diatoms and cryptophytes) in the first weeks after the CWP also strongly influenced the summer populations of the two zooplankton groups. 4. Inter‐annual differences in water temperature during the critical time periods at least partly explained the contrasting responses of cyclopoid copepods and bosminids to heat wave events. 5. Our findings indicate that the zooplankton response to climate warming, particularly to heat wave events, is critically dependent on the temporal pattern of elevated water temperatures. Beyond that, we show that the summer zooplankton populations react to periods of warming in relation to events in the plankton annual cycle (such as the CWP in eutrophic lakes) rather than to warming at a fixed time in the season. 相似文献
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ADRIAN KAMMER FRANK HAGEDORN ILYA SHEVCHENKO† JENS LEIFELD‡ GEORG GUGGENBERGER§ TAMARA GORYACHEVA¶ REAS RIGLING PAVEL MOISEEV¶ 《Global Change Biology》2009,15(6):1570-1583
Historical photographs document that during the last century, forests have expanded upwards by 60–80 m into former tundra of the pristine Ural mountains. We assessed how the shift of the high‐altitude treeline ecotone might affect soil organic matter (SOM) dynamics. On the gentle slopes of Mali Iremel in the Southern Urals, we (1) determined the differences in SOM stocks and properties from the tundra at 1360 m above sea level (a.s.l.) to the subalpine forest at 1260 m a.s.l., and (2) measured carbon (C) and nitrogen (N) mineralization from tundra and forest soils at 7 and 20 °C in a 6‐month incubation experiment. C stocks of organic layers were 3.6±0.3 kg C m?2 in the tundra and 1.9±0.2 kg C m?2 in the forest. Mineral soils down to the bedrock stored significantly more C in the forest, and thus, total soil C stocks were slightly but insignificantly greater in the forest (+3 kg C m?2). Assuming a space for time approach based on tree ages suggests that the soil C sink due to the forest expansion during the last century was at most 30 g C m?2 yr?1. Diffuse reflective infrared spectroscopy and scanning calorimetry revealed that SOM under forest was less humified in both organic and mineral horizons and, therefore, contained more available substrate. Consistent with this result, C mineralization rates of organic layers and A horizons of the forest were two to four times greater than those of tundra soils. This difference was similar in magnitude to the effect of increasing the incubation temperature from 7 to 20 °C. Hence, indirect climate change effects through an upward expansion of forests can be much larger than direct warming effects (Δ0.3 K across the treeline). Net N mineralization was 2.5 to six times greater in forest than in tundra soils, suggesting that an advancing treeline likely increases N availability. This may provide a nutritional basis for the fivefold increase in plant biomass and a tripling in productivity from the tundra to the forest. In summary, our results suggest that an upward expansion of forest has small net effects on C storage in soils but leads to changes in SOM quality, accelerates C cycling and increases net N mineralization, which in turn might stimulate plant growth and thus C sequestration in tree biomass. 相似文献
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A Bayesian CART algorithm 总被引:3,自引:0,他引:3
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ABSTRACT. The effect of allatectomy on synthesis of accessory reproductive gland secretion, spermatophore production and sexual behaviour in male Diploptera punctata was investigated during the first 6 weeks of adult life. After allatectomy, synthesis of the secretion and production of spermatophores was slightly reduced relative to sham-operated animals (by 16%), but not relative to normal animals. However, sexual behaviour of the operated animals appeared normal. Thus, the corpora allata (CA) may not be necessary for the sexual functioning of male D.punctata. The synthesis of C16 juvenile hormone (C16 JH; JH III) by isolated pairs of CA from individual males was followed during this period and, at all times, the rate of synthesis was less than 8pmolh-1 per pair, a rate similar to that observed in pregnant females. The significance of this continued synthesis of JH by male CA is unknown, although it may be related to the maintenance of general metabolic activities. 相似文献
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Transpuparial transmission of Kashmir bee virus and sacbrood virus in the honey bee (Apis mellifera)
When particles of Kashmir bee virus (KBV) and sacbrood virus (SBV) were fed to larvae of the honey bee, Apis mellifera, in Australian colonies, the resulting pupae became in apparently infected. There was no statistically significant difference in the susceptibility of 1, 2, 3 or 4-day-old larvae for either virus, but 5-day-old larvae were significantly less susceptible to SBV than younger larvae. There was no significant difference in the proportions of pupae that became in apparently infected when, as larvae, they were fed various concentrations of each virus, but significantly more larvae were removed from their cells when fed concentrated preparations of each virus than when fed diluted preparations. Susceptible larvae that became in apparently infected with KBV and SBV developed normally into in apparently infected pupae and later, emerged as in apparently infected worker bees. 相似文献
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PETRA A. STIEHL‐BRAUN ADRIAN A. HARTMANN ELLEN KANDELER NINA BUCHMANN PASCAL A. NIKLAUS 《Global Change Biology》2011,17(8):2629-2639
Soil methanotrophic bacteria constitute the only globally relevant biological sink for atmospheric methane (CH4). Nitrogen (N) fertilizers as well as soil moisture regime affect the activity of these organisms, but the mechanisms involved are not well understood to date. In particular, virtually nothing is known about the spatial distribution of soil methanotrophs within soil structure and how this regulates CH4 fluxes at the ecosystem scale. We studied the spatial distribution of CH4 assimilation and its response to a factorial drought × N fertilizer treatment in a 3‐year experiment replicated in two grasslands differing in management intensity. Intact soil cores were labelled with 14CH4 and methanotrophic activity mapped at a resolution of ~100 μm using an autoradiographic technique. Under drought, the main zone of CH4 assimilation shifted down the soil profile. Ammonium nitrate (NH4NO3) and cattle urine reduced CH4 assimilation in the top soil, but only when applied under drought, presumably because NH4+ from fertilizers was not removed by plant uptake and nitrification under these conditions. Ecosystem‐level CH4 fluxes measured in the field did show no or only very small inhibitory effects, suggesting that deeper soil layers fully compensated for the reduction in top soil CH4 assimilation. Our results indicate that the ecosystem‐level CH4 sink cannot be inferred from measurements of soil samples that do not reflect the spatial organization of soils (e.g. stratification of organisms, processes, and mechanisms). The autoradiographic technique we have developed is suited to study methanotrophic activity in a relevant spatial context and does not rely on the genetic identity of the soil bacterial communities involved, thus ideally complementing DNA‐based approaches. 相似文献
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VALERIE P. SAXTON IVO MULDER GLEN L. CREASY ADRIAN M. PATERSON JAMES G. ROSS MICHAEL C. T. TROUGHT 《Austral ecology》2011,36(3):233-239
Secondary metabolites in fruit are compounds that are not directly associated with plant growth; some are directly related to plant reproductive processes, specifically seed protection and dispersion. There is a complex and species‐specific interaction between these plant compounds and their avian seed dispersers. To determine whether two important secondary metabolites in wine grapes – tannins and colour pigments – might be important cues to two of the avian species that forage on wine grapes, and how species‐specific this interaction might be, comparative field experiments were run with Australasian silvereyes (Zosterops lateralis) and European blackbirds (Turdus merula). Both species were offered a glucose/fructose artificial nectar with increasing concentrations of grape tannins. In a second experiment, they were offered both green and purple artificial grapes where only the colour differed. Both species showed aversion to tannins; silvereyes appeared to have greater tolerance than blackbirds of tannin concentrations above 5%. In summer no preference was shown between green and purple coloured artificial grapes, but in late autumn blackbirds took only purple grapes whereas silvereyes pecked mostly at green. Links between tannin for seed protection and colour signals to birds are discussed. Colour may cue the two species to different species‐specific aspects of fruit nutritive value. 相似文献