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Continuous Darkness (continuous + darkness)
Selected AbstractsKleptoplasty in an Antarctic dinoflagellate: caught in evolutionary transition?ENVIRONMENTAL MICROBIOLOGY, Issue 1 2007Rebecca J. Gast Summary Photosynthetic dinoflagellates contain a diverse collection of plastid types, a situation believed to have arisen from multiple endosymbiotic events. In addition, a number of heterotrophic (phagotrophic) dinoflagellates possess the ability to acquire chloroplasts temporarily by engulfing algae and retaining their chloroplasts in a functional state. These latter relationships typically last from a few days to weeks, at which point the chloroplasts lose function, are digested and replaced with newly acquired plastids. A novel and abundant dinoflagellate related to the icthyotoxic genera Karenia and Karlodinium was recently discovered by us in the Ross Sea, Antarctica. Sequencing of its plastid small subunit ribosomal gene indicated that it did not share evolutionary history with the plastids of Karenia or Karlodinium, but was closely related to the free-living haptophyte Phaeocystis antarctica, a species that often dominates phytoplankton blooms in the Ross Sea. Chloroplast uptake was observed to occur rapidly (within 2 days), with retention in cultures being long-lived (several months) but not permanent. The dinoflagellate was also incapable of growing indefinitely in continuous darkness with algae as prey. Our findings may indicate an emerging endosymbiotic event yielding a dinoflagellate that is presently neither purely phototrophic nor purely heterotrophic, but occupies a niche juxtaposed between these contrasting nutritional modes. [source] Effect of stimulation of endogenous melatonin secretion during constant light exposure on 6-sulphatoxymelatonin rhythmicity in ratsJOURNAL OF PINEAL RESEARCH, Issue 1 2000D.J. Kennaway When light is presented unexpectedly at night to rats, melatonin production and secretion is acutely inhibited and the time of onset of production on the subsequent night is altered. In a series of experiments, we examined the effects of 6,12 hr light (200 lux) at night on melatonin metabolite excretion (6-sulphatoxymelatonin, aMT.6S). During the light exposure, we administered isoproterenol to stimulate endogenous production of melatonin by the pineal gland to determine if replacement of melatonin would block any phase shifting effects of the light. Exposure to 6 hr of light either during the first or second half of the night suppressed aMT.6S excretion during the light treatment and delayed the onset of melatonin secretion by 3.7±0.6 and 2.5±0.6 hr, respectively, compared to a change of 0.5±0.1 hr in animals maintained in darkness. Twelve hours light exposure (i.e. one night of continuous light) suppressed aMT.6S excretion completely and resulted in a delay in the onset the next night of 2.1±0.7 hr. When propranolol (10 mg/kg) was administered at 2-hr intervals during darkness, aMT.6S excretion was suppressed throughout the night, but on the subsequent release into constant darkness the onset of excretion was not delayed (0.6±0.1 hr delay). Administration of isoproterenol (10 mg/kg) to animals in constant light, at the time of expected lights off (CT12), and 5 hr later (CT17) resulted in an increase in melatonin production and aMT.6S excretion that was similar in duration and amount to the control night. The stimulation of endogenous melatonin production failed to block the phase shifting effects of the light exposure and, in fact, appeared to potentiate the delay at least on the first night (4.2±0.9 hr). The timing of the release into constant darkness following the light treatment had an unexpected effect on melatonin production on the cycle after treatment. Thus, animals exposed to 12 hr light and released into darkness at the normal time of lights off as above had a delay of about 2 hr and excreted 71±18% of the aMT.6S excreted on a control night. Animals released into darkness at the expected time of lights on failed to excrete more than 20 pmol/hr (i.e. no onset of excretion could be determined) at any time on the first subjective night after light treatment, which was no different from the excretion during the light treatment. On the next subjective night, the onset was delayed as expected and the amount of aMT.6S produced was restored. Treatment with isoproterenol at CT12 and CT17 failed to affect either the amount of aMT.6S excreted on the first subjective night after light treatment or the phase delay on the second night after treatment. The failure to produce melatonin on the first subjective night after 12 hr light exposure and release into darkness at CTO was not due to failure at the level of the pineal gland since injection of isoproterenol at CT12 and CT17 on the first subjective night after light restored the normal amount of melatonin production. These results suggest that the absence of melatonin during light stimulation at night is not responsible for the phase delay in melatonin production and excretion on subsequent nights. The basis of the failure of the rats to commence melatonin production following 12 hr extended light exposure followed immediately by continuous darkness is not known. [source] Diapause-inducing signals prolong nymphal development in the two-spotted spider mite Tetranychus urticaePHYSIOLOGICAL ENTOMOLOGY, Issue 3 2009TAKESHI SUZUKI Abstract Female two-spotted spider mite Tetranychus urticae are grown under different photoperiods and the photoperiodic regulation of diapause is examined. The photoperiodic response curve for diapause induction was of the long day,short day type, with critical day lengths (CDLs) of 2 and 12.5 h; diapause was induced between these CDLs. The preimaginal period is significantly longer in diapausing females than in non-diapausing females; moreover, a significant positive correlation is detected between diapause incidence and deutonymphal period. Diapause incidence is high when long-night photoperiods are applied against a background of continuous darkness in the stages including the deutonymph; this stage appears to be the most sensitive to photoperiod. These observations suggest that diapause-inducing conditions inhibit nymphal development, particularly in the deutonymphal stage when photoperiodic time measurement for determination of reproduction or diapause is carried out. [source] Effects of thermoperiods on diapause induction in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)PHYSIOLOGICAL ENTOMOLOGY, Issue 5 2004Xiao-Ping Wang Abstract., The effects of thermoperiods on diapause induction in continuous darkness or under a 12 : 12 h LD photoperiod were investigated in the cabbage beetle, Colaphellus bowringi Baly, a typical short-day species. The diapause response curves both at different constant temperatures and at the thermocycle of format CT x: (24 , x) h (16 : 28 °C) under continuously dark rearing conditions showed that the incidence of diapause depended mainly on whether or not the mean temperature was ,20 °C or >20 °C. If the mean temperature was ,20 °C, all individuals entered diapause; if >20 °C, the incidence of diapause declined gradually with increasing mean temperatures. The thermocycle (CT 12 : 12 h) with a series of different cryophases (8,22 °C) and thermophases (24,32 °C) under continuous darkness demonstrated a cryophase response threshold temperature of approximately 19 °C and a thermophase response threshold temperature of approximately 31 °C. Thermoperiodic amplitude (temperature difference between cryophase and thermophase) was shown to have a significant influence on diapause induction at the mean temperatures of 22, 23 and 24 °C, but not at ,25 °C. Thermoperiodic responses under LD 12 : 12 h clearly showed that the incidence of diapause was influenced strongly by the photophase temperature. The thermoperiod under LD 12 : 12 h induced a much lower incidence of diapause than the thermoperiod with the same temperature in continuous darkness. The ecological significance of thermoperiodic induction of diapause in this species is discussed. [source] Somatic growth, survival, feed utilization and starvation in European elver Anguilla anguilla (Linnaeus) under two different photoperiodsAQUACULTURE RESEARCH, Issue 5 2009A Rodríguez Abstract The aim of the study was to determine the effect of two photoperiod regimes under artificial conditions on growth performance and survival in the European eel Anguilla anguilla during the transition from glass eel to elver. The fish were held in 12-h-light:12-h-dark (12L:12D) and in continuous darkness (DD) in fed and fast trials lasting 80 days. Fed fish kept in the dark showed higher somatic growth, and a better feed conversion ratio, higher protein and lipid content, with significant differences between treatments. Dark environment increased the survival rate in comparison with fish exposed to 12L:12D, during which eels showed lower survival rates and greater variations in size. Fasted fish suffered loss of body mass in both photoperiods at the end of the experimental phase, but fish exposed to 12L:12D lost more body mass. These results indicate that the photoperiod is a key factor during the glass eel,elver stage, which may contribute to optimizing the early stages of eel culture. [source] | ||||||||||