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Some major aspects of insect life, like development time and reproduction, can benefit from fluctuating temperatures rather than a constant temperature regime. The benefit of fluctuating temperature has generally been attributed to the non-linear properties of the relationship of many life history traits with temperature. Daily temperature rise, however, usually coincide with the light phase of the photoperiodic cycle and there could be a benefit in linking daily temperature fluctuations with light and dark phases e.g. to anticipate the change in temperature. Such synergistic effects have primarily been studied in the light of activity patterns and gene expression, but have not yet been shown to extend to population dynamics and aspects of individual fitness like oviposition behavior. We therefore explored possible synergistic effects on life history traits of the springtail Orchesella cincta . We first test the primary effect of ecologically relevant temperature fluctuations of different amplitudes on population growth and total population mass. The slowest population growth was observed in the constant temperature regime treatment and the highest population growth in the regime with high amplitude fluctuations. In a second experiment, population growth and oviposition rhythm were measured under four different regimes; a constant light and temperature regime, thermoperiod only, photoperiod only and thermoperiod and photoperiod aligned as under natural conditions. The regime in which thermoperiod was aligned with photoperiod resulted in a higher population growth than could be realized by either factor alone. Also, significantly fewer eggs were laid in the constant temperature/light regime than in the other three regimes, strongly suggesting that this regime is stressful to O. cincta . Additionally, the fraction of eggs laid at night was highest in the regime with the combined temperature and light cycle. In conclusion, our results show that under these experimental conditions there is a synergistic effect of daily temperature fluctuations in combination with light/dark phases that can considerably influence important life history traits and affect behavior. Such effects are likely to be relevant under natural conditions. [ABSTRACT FROM AUTHOR]

The timing and pattern of mammalian behavioral activities are regulated by an evolutionary optimized interplay of the genetically based biological (circadian) clock located in the brain's suprachiasmatic nuclei and direct responses to environmental factors that superimpose and thus mask the clock-mediated effects, the most important of which is the photically induced phase-setting (synchronization) of the circadian rhythmicity to the 24-hour solar day. In wild and captive animals living under the natural conditions prevailing in their habitat, to date, only a few attempts have been made to analyze the role of these two regulatory mechanisms in the species' adaptation to the time structure prevailing in their habitat. We studied the impact of housing conditions and season on the daily timing and pattern of activity in Mexican spider monkeys ( Ateles geoffroyi). To this end, we carried out long-term activity recordings with Actiwatch® AW4 accelerometer/data-logger devices in 11 adult Ateles living under identical natural lighting and climatic conditions in either a large wire netting cage or a 0.25 ha forest enclosure in the primatological field station of Veracruz State University near Catemaco, Mexico. In a gravid female in the forest enclosure, we obtained first-hand information on the effect of late pregnancy and parturition on the monkey's activity rhythm. The Ateles behaved strictly diurnal and undertook about 90% of daily total activity during this activity time. Due to a higher second activity peak in late afternoon, the bimodal activity pattern was more pronounced in monkeys living in the forest enclosure. Although the spider monkeys kept there had an earlier activity onset and morning activity peak than their conspecifics in the cage, no consistent differences were found in the parameters characterizing the phase-setting of the circadian system to the environmental 24-h periodicity, either by comparison or correlation with the external time markers of sunrise (SR) and sunset (SS). The most obvious effect of late pregnancy, parturition and lactation was a distinct reduction of the activity level during the week of parturition and the next. Seasonal variations in the form of significant differences between the long-day summer half year and the short-day winter half year were established in the phase-angle differences of the morning activity peak to SR, in the evening activity peak and activity offset to SS, as well as in the activity time and the peak-to-peak interval, but not in the phase position of activity onset to SR or in the height of the morning and evening activity peak. These findings in combination with a high variability of the phase angle differences indicate that in A. geoffroyi, a relatively weak circadian component and strong masking direct effects of environmental factors are involved in the regulation of the daily activity rhythm. [ABSTRACT FROM AUTHOR]

The endogenous circadian clock is entrained by external cues, mainly the light-dark cycle received by photopigments located in the retina. The authors investigated (1) the effect of aging on the synchronization of the rest-activity rhythm and (2) the physiological basis of light photoreception in the gray mouse lemur, a nocturnal Malagasy primate. Old individuals were tested at different irradiance levels under 3 different light wavelengths previously shown to trigger maximal response in young adults. Investigators analyzed animal activity and temperature waveforms and used 2 reference treatments, strong white light and continuous darkness. The investigation revealed manifold effects of aging picturing a general loss of responsiveness to light and age-related changes in activity and temperature. In addition, the investigation shows that photoentrainment is a continuous process. Short wavelengths (430 nm) are more efficient than longer wavelengths (470-540 nm) at low light levels at dawn and across all light levels at dusk. This suggests an implication of S-cones, differential at dawn and dusk. This results, surprising for several reasons, calls for further investigation. The study brings an interesting contribution to the understanding of the physiological processes underlying synchronization to light. [ABSTRACT FROM PUBLISHER]

The mammalian endogenous circadian clock, the suprachiasmatic nuclei, receives environmental inputs, namely the light-dark cycle, through photopigments located in the eye and from melanopsin-expressing retinal ganglion cells. The authors investigated the influence of light wavelength and intensity on the synchronization of the rest-activity rhythm of the gray mouse lemur, a nocturnal Malagasy primate. Animals were tested at different irradiance levels (320, 45, 13, and 6 nmol.m-2.s-1) under several light wavelengths (from 400 to 610 nm). Several parameters including circadian period, activity, and body temperature waveforms were used to assess synchronization to a 12:12 light-dark cycle in comparison to control treatments (12:12 white light or continuous darkness). Entrainment of the circadian rest-activity cycle increased with light intensity. It was more efficient for mid wavelengths relative to shorter or longer wavelengths but not coincident with melanopsin maximal sensitivity, suggesting other photoreceptors are likely involved in lemurs' photoentrainment. The authors obtained a novel synchronization pattern characterized by a clear synchronization to lights-on only without phasing to lights-off. Changes in photo-responsiveness at dusk and dawn highlight differential responses of evening and morning oscillators in the circadian clock. [ABSTRACT FROM AUTHOR]

Daily light and temperature cycles are considered the most important zeitgebers for circadian clocks in many organisms. The influence of each single zeitgeber on the clock has been well studied, but little is known about any synergistic effects of both zeitgebers on the clock. In nature, light and temperature show characteristic daily oscillations with the temperature rising during the light phase and reaching its maximum in the late afternoon. Here, we studied behavioral and molecular rhythms in Drosophila melanogaster under simulated natural low light-dark (LD) and temperature (T) cycles that typically occur during the September equinox. Wild-type flies were either subjected to simulated LD or T cycles alone or to a combination of both. Behavioral rhythms and molecular rhythms in the different clock neurons were assessed under the 3 different conditions. Although behavioral rhythms entrained to all conditions, the rhythms were most robust under the combination of LD and T cycles. The clock neurons responded differently to LD and T cycles. Some were not entrained by T cycles alone; others were only slightly entrained by LD cycles alone. The amplitude of the molecular cycling was not different between LD alone and T cycles alone; but LD alone could set the pacemaker neurons to similar phases, whereas T cycles alone could not. The combination of the 2 zeitgebers entrained all clock neurons not only with similar phase but also enhanced the amplitude of Timeless cycling in the majority of cells. Our results show that the 2 zeitgebers synergistically entrain behavioral and molecular rhythms of Drosophila melanogaster. [ABSTRACT FROM AUTHOR]

Studies a Mapuche native community in Patagonia, Argentina that has no access to electricity and artificial light in order to gain better understanding of the role of natural environmental signals in circadian and seasonal entrainment. Diurnal and seasonal variations; Environmental variables, including photoperiod, temperature and rainfall; Patterns of disease and medical visits.

Abstract: The objective of the present work is to develop and calibrate a novel, vertical solid particle injector that uses the pressure drop in the air flow across an orifice plate in a circular pipe, to naturally entrain micron-sized solid particles such as coal dust. The particles continuously drop from a feeder located outside the pipe into the orifice plate through peripheral (side) openings in the pipe, where they are carried upwards by the air flow accelerated near the orifice exit. Three types of designs for the peripheral openings, in terms of the shape, size and number are evaluated by testing which one of them results in maximum particle entrainment. The device is calibrated by recording the mass loss rate of the powder as a function of volumetric flow-rate of air. The results show that there is an optimum area for the side openings, at which the injector performance will be the best for the given pipe and orifice-hole sizes. The entrainment rate is found to be a non-linear function of the flow-rate for low air flow-rates (till around 9.4g per minute) and for higher air flow-rates it becomes an almost linear function. [Copyright &y& Elsevier]