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Constant Conditions (constant + condition)
Selected AbstractsMaternal size and age affect offspring sex ratio in the solitary egg parasitoid Anaphes nitensENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 1 2007Serena Santolamazza-Carbone Abstract In this study, the effects of maternal age, diet, and size on offspring sex ratio were investigated for the solitary egg parasitoid, Anaphes nitens Girault (Hymenoptera: Mymaridae), both outdoors, during the winter, and inside a climatic chamber under favourable constant conditions. During the winter of 2005,2006, each of seven groups containing 40 1-day-old females was mated and randomly distributed among two treatments: (treatment 1) a droplet of undiluted honey ad libitum + one fresh egg capsule of the snout beetle Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae) as host; (treatment 2) drops of water + one fresh egg capsule of G. scutellatus. We recorded the lifetime fecundity, the daily sex allocation, and the lifetime offspring sex ratio to study the existence of a relationship with maternal characteristics. Moreover, we assessed the effect of location (outdoors vs. indoors) and group (groups are representative of early, mid, and late winter) on sex ratio. The most important factor that biased the sex ratio was maternal body size: larger females of both treatments produced more female offspring. As females of A. nitens could gain more advantage than males from body size, larger mothers have a higher fitness return if they produce more daughters. The effect of the treatment was significant: starved females produced more females. Location and group were not significant. Fecundity and sex ratio were age dependent. Old mothers that received honey (treatment 1) had fewer offspring and a more male-biased offspring sex ratio, probably due to reproductive senescence and sperm depletion. Starved females (treatment 2) experienced reproductive decline earlier, perhaps because they invested more energy in maintenance rather than in reproduction. [source] Spatial and temporal variation of passer Per2 gene expression in two distinct cell groups of the suprachiasmatic hypothalamus in the house sparrow (Passer domesticus)EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2002Ute Abraham Abstract In mammals, the major pacemaker controlling circadian rhythmicity is located in the hypothalamic suprachiasmatic nuclei. Although there is evidence for the presence of a hypothalamic circadian oscillator in birds from lesioning studies, neuroanatomical, neurochemical and functional investigations have failed to identify its exact location. Two cell groups in the avian hypothalamus have been shown to bear characteristics of the mammalian suprachiasmatic nucleus: the suprachiasmatic nucleus and the lateral hypothalamic retinorecipient nucleus. We cloned an avian period homologue (pPer2) and investigated the temporal and spatial expression pattern of this gene in the house sparrow hypothalamus using in situ hybridization. Applying quantitative morphometry, we found rhythmic expression of pPer2 during light,dark as well as in constant conditions in the suprachiasmatic nucleus and in the lateral hypothalamus. The temporal and spatial distribution of pPer2 expression in the suprachiasmatic nucleus suggest a longitudinal compartmentalization of the nucleus with period gene expression being initiated in the most rostral portion of the suprachiasmatic nucleus before lights on. In the lateral hypothalamus, phasing of pPer2 -rhythmicity appeared different from the suprachiasmatic nucleus. The major difference between light,dark and constant conditions was a decrease in the amplitude of pPer2 rhythmicity in the suprachiasmatic nucleus. Our data demonstrate that, unlike in mammals, Per gene expression in the suprachiasmatic hypothalamus of the house sparrow is not confined to a single cell group, indicating a more complex organization of the circadian oscillator in the hypothalamus of birds. [source] Growth rates of phytoplankton under fluctuating lightFRESHWATER BIOLOGY, Issue 2 2000Elena Litchman Summary 1The effect of light fluctuations on the growth rates of four species of freshwater phytoplankton was investigated. Experimental light regimes included constant irradiance and fluctuations of a step function form, with equal proportion of high (maximum of 240 µmol photons m -2 s -1) and low light (minimum of 5 µmol photons m -2 s -1) (or dark) in a period. Fluctuations of 1, 8 and 24-h periods were imposed over several average irradiances (25, 50, 100 and 120 µmol photons m -2 s -1). 2Growth rate responses to fluctuations were species-specific and depended on both the average irradiance and the period of fluctuations. Fluctuations at low average irradiances slightly increased growth rate of the diatom Nitzschia sp. and depressed growth of the cyanobacterium Phormidium luridum and the green alga Sphaerocystis schroeteri compared to a constant irradiance. 3Fluctuations at higher average irradiance did not have a significant effect on the growth rates of Nitzschia sp. and Sphaerocystis schroeteri (fluctuations around saturating irradiances) and slightly increased the growth rates of the cyanobacteria Anabaena flos-aquae and Phormidium luridum (when irradiance fluctuated between limiting and inhibiting levels). 4In general, the effect of fluctuations tended to be greater when irradiance fluctuated between limiting and saturating or inhibiting levels of a species growth-irradiance curve compared to fluctuations within a single region of the curve. 5The growth rates of species under fluctuating light could not always be predicted from their growth-irradiance curves obtained under constant irradiance. When fluctuations occur between limiting and saturating or inhibiting irradiances for the alga and when the period of fluctuations is long (greater than 8 h), steady-state growth-irradiance curves may be insufficient to predict growth rates adequately. Consequently, additional data on physiological acclimation, such as changes in photosynthetic parameters, may be required for predictions under non-constant light supply in comparison to constant conditions. [source] Clarification of date juiceINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 3 2003Mohamed A. Al-Farsi Summary This study was initiated to utilize a variety of low quality dates (Qish-Habash) so that high quality syrup could be produced by modifying the clarification process of the date juice. Five different clarification treatments were used: (1) filtration, (2) hot liming and filtration, (3) cold liming and filtration, (4) powder-activated carbon and filtration, and (5) granular-activated carbon and filtration. The sugar content, total soluble solids, total ash, pH, colour and purity were analysed to determine the clarification effects. The clarified juices produced by these treatments were evaporated under constant conditions to produce date syrup. Filtration, and activated carbon and filtration were the most successful treatments for the clarification of the date juice. Filtration gave the highest improvement in syrup purity (97.7%), due to the reduction of total ash by 19.5% and colour by 44.6%. Activated carbon removed the juice colour to give the lowest amount (60% in powder form and 57% in granular form), as well as reducing total ash, which led to an improved syrup purity, 92.2% in powder form and 91.4% in granular form. Liming clarification had undesirable effects, by increasing the total ash (15% in hot and 17% in cold lime), and increasing the colouring matter produced by decomposition. [source] Rapid Holocene chemical weathering on a calcitic lake shoreline in an alpine periglacial environment: Attgløyma, Sognefjell, southern NorwayPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2006Geraint Owen Abstract A small lake (Attgløyma) at an altitude of about 1220,m in the low-alpine zone, southern Norway, has a shore platform in calcitic and quartzitic muscovite-chlorite schists. The platform has recently been exposed by a fall in lake level due to upstream dam construction and exhibits micro-landforms ranging from pits and grooves to upstanding crenulate ridges produced by differential chemical weathering under relatively constant conditions over the last ca. 10,000 years. The maximum surface lowering rate of the calcitic layers estimated from differential weathering is 35,mm,ka,1, which is about an order of magnitude greater than most previous estimates from alpine and polar periglacial environments. Average bedrock surface lowering across the whole platform reached a maximum of 15.5,±,2.2,mm,ka,1 in a vertical zone corresponding with the former lake level, declining to negligible values around 0.7,m below lake level. Differential weathering and bedrock surface lowering were also negligible immediately above lake level. Correspondence of maximum surface lowering rates with the former lake level and a shoreline notch at the back of a platform suggest that the effects of solutional weathering of the calcite have been enhanced by water movement generated by small lake-surface waves. Copyright © 2006 John Wiley & Sons, Ltd. [source] The circatidal rhythm of the estuarine gastropod Hydrobia ulvae (Gastropoda: Hydrobiidae)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2010SÓNIA VIEIRA Intertidal animals display a suite of cyclic behaviours that evolved as adaptations to the predictable cycle of inundation and exposure. In estuarine habitats, mud snails from the genus Hydrobia are among the most abundant grazers, and have received considerable attention with respect to the behavioural mechanisms mediating locomotion, dispersal, and feeding, although the nature of the control of these processes has remained elusive. In particular, it is not clear whether endogenous activity patterns are related to periodic changes of microphytobenthos biomass at the sediment surface, or whether they are timed to the tidal cycle at all. In the present study, we address the crawling activity of Hydrobia ulvae under constant conditions, as well as the effects of individual size and previous short-term exposure to tides of different range, by recording immersed individual snails under constant dark conditions. We show that the species displays an overt circatidal pattern of crawling, with activity peaks around high water, and that the start of inundation may act as an entrainment agent of the rhythm. Moreover, the results obtained indicate that smaller snails display higher levels of activity, although neither the size nor previous in situ influence of tidal range has an effect on the period and on the amplitude of the rhythm. These findings suggest that fluctuations of microphytobenthos biomass are not a sufficiently strong selective pressure to have shaped locomotor activity in H. ulvae. Moreover, feeding of H. ulvae should take place mostly during high water and be independent of periodic fluctuations of microphytobenthos biomass at the surface of the sediment. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 439,450. [source] | ||||||||||