Low Ambient Light Research Articles

Experimental shading alters leaf litter breakdown in streams of contrasting riparian canopy cover

Summary 1. Headwater stream ecosystems are primarily heterotrophic, with allochthonous organic matter being the dominant energy. However, sunlight indirectly influences ecosystem structure and functioning, affecting microbial and invertebrate consumers and, ultimately, leaf litter breakdown. We tested the effects of artificial shading on litter breakdown rates in an open-canopy stream (high ambient light) and a closed-canopy stream (low ambient light). We further examined the responses of invertebrate shredders and aquatic hyphomycetes to shading to disentangle the underlying effects of light availability on litter breakdown. 2. Litter breakdown was substantially slower for both fast-decomposing (alder, Alnus glutinosa) and slow-decomposing (beech, Fagus sylvatica) leaf litters in artificially shaded stream reaches relative to control (no artificial shading) reaches, regardless of stream type (open or closed canopy). 3. Shredder densities were higher on A. glutinosa than on F. sylvatica litter, and shading had a greater effect on reducing shredder densities associated with A. glutinosa than those associated with F. sylvatica litter in both stream types. Fungal biomass was also negatively affected by shading. Results suggest that the effects of light availability on litter breakdown rates are mediated by resource quality and consumer density. 4. Results from feeding experiments, where A. glutinosa litter incubated under ambient light or artificial shade was offered to the shredder Gammarus fossarum, suggest that experimental shading and riparian canopy openness influenced litter palatability interactively. Rates of litter consumption by G. fossarum were decreased by experimental shading in the open-canopy stream only. 5. The results suggest that even small variations in light availability in streams can mediate substantial within-stream heterogeneity in litter breakdown. This study provides further evidence that changes in riparian vegetation, and thus light availability, influence organic matter processing in heterotrophic stream ecosystems through multiple trophic levels.

The influence of ambient light intensity on in situ laser diffractometers

In situ laser diffractometers characterize the suspended particle size distribution (PSD) by measuring laser‐generated light scattered off small particles over a range of small forward angles. In environments with low particulate concentrations or high ambient light conditions the ratio of natural downwelling sunlight to scattered laser light sensed by the photodetectors is high and measurements are influenced. Here, we evaluate the effect of the ambient light field intensity on measurements made with a Laser In Situ Scattering and Transmissometry (LISST) 100X type B instrument. Paired light‐dark scattering distributions are recorded over a range of underwater light intensities in high‐turbidity and low‐turbidity water. Light measurements displayed large erroneous concentrations of particles in the smallest size bin (1.25–1.48 μm) and showed effects over the full range of the PSD. Ambient light was found to exhibit the same constant distribution over the instrument photodetectors in both water samples, although the magnitude of the response, in laser counts per unit ambient light intensity, was PSD dependent. A technique for postprocessing data to remove the influence of light is presented for moored deployment and vertical profile data collected at Lake Tahoe, California‐Nevada, United States. While measurements removed of the light effect were successfully reconstructed, the technique may not be applicable to data where the PSD or the LISST orientation relative to the sun direction change rapidly or when light intensities are high enough to quench the instrument photodetectors. Ambient light was found to have negligible effects on PSD measurements in Lake Tahoe was below intensities of ∼30 W m−2.

Impact of ambient bright light on agitation in dementia

To evaluate the effect of ambient bright light therapy (BLT) on agitation among institutionalized persons with dementia. High intensity, low glare ambient lighting was installed in activity and dining areas of a state psychiatric hospital unit in North Carolina and a dementia-specific residential care facility in Oregon. The study employed a cluster-unit crossover design involving four ambient lighting conditions: AM bright light, PM bright light, All Day bright light, and Standard light. Sixty-six older persons with dementia participated. Outcome measures included direct observation by research personnel and completion by staff caregivers of the 14-item, short form of the Cohen-Mansfield Agitation Inventory (CMAI). Analyses of observational data revealed that for participants with mild/moderate dementia, agitation was higher under AM light (p = 0.003), PM light (p < 0.001), and All Day light (p = 0.001) than Standard light. There was also a trend toward severely demented participants being more agitated during AM light than Standard light (p = 0.053). Analysis of CMAI data identified differing responses by site: the North Carolina site significantly increased agitation under AM light (p = 0.002) and PM light (p = 0.013) compared with All Day light while in Oregon, agitation was higher for All Day light compared to AM light (p = 0.030). In no comparison was agitation significantly lower under any therapeutic condition, in comparison to Standard lighting. Ambient bright light is not effective in reducing agitation in dementia and may exacerbate this behavioral symptom.

The eye of the parthenogenetic and minute moth Ectoedemia argyropeza (Lepidoptera: Nepticulidae)

Ectoedemia argyropeza (Zeller, 1839) possesses a compound eye that exhibits features of both apposition and superposition type eyes. Like apposition eyes, the eye of E. argyropeza lacks a clear-zone, which in superposition eyes separates the distal dioptric from the proximal light-perceiving structures. On the other hand, a tracheal layer around the proximal ends of the rhabdom as well as a well-developed corneal nipple array on the corneal surfaces are features that E. argyropeza shares with the larger moths. Unique, and so far only seen to this extreme degree in any insect, is the hourglass-shape of E. argyropeza's rhabdom, in which two almost equally voluminous regions (one distal, one proximal and formed in both cases by seven rhabdomeres) are connected by a narrow waist-like region of the retinula. An eighth retinula cell, not participating in rhabdom formation, is developed as a basal cell, just above the basement membrane. The eye responds with photomechanical changes to dark/light adaptation, but while the proximal rhabdom moiety slightly expands (as expected) in the dark, the distal rhabdom increases its diameter only upon light-adaptation. Owing to the tandem position of the two rhabdom moities, it is in the light-adapted state that the distally-placed rhabdom is favoured, while the proximal rhabdom plays a more important role at low ambient light levels. With screening pigments withdrawn, tracheal tapetum exposed, and distal rhabdom diameters reduced, the proximal and in the dark enlarged rhabdom is then in a position to capture photons that have entered the eye through not only the ommatidial window above, but other facets as well even in the absence of a clear-zone and superposition optics.

Bottlenose Dolphin (&lt;I&gt;Tursiops truncatus&lt;/I&gt;) Double-Slit Pupil Asymmetries Enhance Vision

Geometries of the iris, retinal cell distributions, and the optical characteristics of the lens and cornea have evolved to optimize the visual adaptations of the bottlenose dolphin (Tursiops truncatus) to the oceanic environment. Under high ambient light conditions, the operculum of the iris shields the lens and forms two asymmetrical slit pupils. Under these conditions, light entering the eye is channeled and focused onto the two areas of the retina having a finer retinal mosaic of ganglion cells (typically associated with higher image resolution). The paths of light determined by tracing rays in the reverse direction through these pupils coincide with a dolphin’s behaviorally observed preferred viewing directions. These rays aid in determining the interdependence between the graininess of the retinal mosaic and resolution spot sizes in the object space. For oblique forward and downward viewing directions in air, the larger temporal pupil admits light which passes through the weakly refractive margin of a bifocal lens, counterbalancing the optically strong cornea in air. In water, light passing through the optically strong lens core is focused from a wide lateral and downward field-of-vision. Although other explanations for comparable aerial and underwater vision remain plausible, a dolphin eye model incorporating a bifocal lens offers an explanation consistent with ophthalmoscopic refractive state measurements. The model is also consistent with visual acuity study results conducted in air and in water under both high and low ambient light levels. From insight gained after applying a common data analysis technique to visual acuity studies conducted by other researchers and tracing oblique rays through the asymmetric double-slit pupils, a re-examination of explanatory hypotheses for the paradoxical observations of comparable aerial and underwater vision is presented. Based in part on these findings and supportive evidence from dolphin vision researchers, the unique distinguishing characteristics of dolphin vision are summarized.

Detection of fruit by theCerrado's marmoset (Callithrix penicillata): modeling color signals for different background scenarios and ambient light intensities

Among placental mammals, only primates have trichromatic color vision, however this is not a uniform condition. Under different genetic status, Old World monkeys have routine trichromacy, while New World monkeys show a visual polymorphism, characterized by obligatory male dichromacy. The ecological role of this genetic difference still remains unclear, but some studies show that dichromats and trichromats appear to have different abilities in detecting colored targets against a background of leaves. The Cerrado's marmoset (Callithrix penicillata) is known to forage in brightly illuminated (savanna-like vegetation) and dimly illuminated (forests) environments, exploiting a high amount of dark fruits. Hence, it seems to be a good model for studying the differential advantages enjoyed by each color vision phenotype under natural conditions. Our aim was to verify how the different phenotypes of Cerrado's marmoset detect components of their diet, evaluating the existence of differential phenotype advantages. Under two different light conditions, visual signals of naturally consumed fruits were modeled against different backgrounds scenarios. Even though dichromats and trichromats appear to be equally suited for tasks involving fruit detection, phenotype differential advantages are observed in this marmoset. In many conditions trichromats are predicted to perform better than dichromats, but under low ambient light dichromats manage to outperform trichromats in some scenarios. Phenotypes that carry widely spaced and longer M/L pigments enjoy the most advantage. These differential performances of trichromatic phenotypes, together with overdominance selection, seem to explain the maintenance of the tri-allelic system found in callitrichids.

The Influence of Increased Ambient Lighting on Mass Detection in Mammograms

Recent research has provided evidence that in reading rooms equipped with liquid crystal displays (LCDs), a measured increase of ambient lighting may improve clinicians' detection performance. In agreement with this research, the American College of Radiology (ACR) has recommended a moderate increase of ambient lighting in mammography reading rooms. This study was designed to examine the effect of a controlled increase of ambient lighting in mammography reading rooms on the diagnostic performance of breast imaging radiologists. Four breast imaging radiologists read 86 mammograms (43 containing subtle cancerous masses and 43 normal) under low (E = 1 lux) and elevated (E = 50 lux) ambient lighting levels on a Digital Imaging and Communications in Medicine-calibrated, medical-grade LCD. Radiologists were asked to identify cancerous masses and to rate their detection confidence. Observer areas under the curve (AUCs) were calculated using a receiver-operating characteristic analysis of fully paired results. Additionally, average observer selection times under both ambient lighting levels were determined. Average radiologist AUCs decreased with elevated ambient lighting (0.78 +/- 0.03 to 0.72 +/- 0.04). Observer performance differences, however, were of the same order of magnitude as interobserver variability and were not statistically significant. Average selection times under increased ambient lighting remained constant or decreased, with the greatest decrease occurring for false-positive (20.4 +/- 18.9 to 14.4 +/- 9.6 seconds) and true-positive (18.0 +/- 13.8 to 12.9 +/- 9.4 seconds) selections. The results agree with those of previous studies in that observer performance differences under a controlled increase of ambient lighting are not statistically significant. On the basis of these findings and ACR guidelines, a moderate increase of ambient lighting in mammography reading rooms is still suggested, but further research with additional cases and observers should be considered.

Cone-Rod Dependence in the Rat Retina: Variation with the Rate of Rod Damage

To assess the effect of accelerated rod damage on the integrity of cones in the rat retina. Rhodopsin-mutant P23H-3 and Sprague-Dawley (SD) rats were raised in scotopic ambient conditions (12 hours dark, 12 hours 5 lux) and then exposed to photopic conditions (12 hours dark, 12 hours 300 lux). Rods and cones were assessed for cell death, outer segment (OS) morphology, and electroretinogram (ERG) responses. Cones in the P23H-retina were affected rapidly by photopic exposure. Exposure for 2 days caused 50% reductions in LM- and S-cone OS length and cone ERG responses, associated with and preceded by reductions in rod OS length and ERG responses. Although 2 days' exposure increased the rate of rod death, outer nuclear layer thinning was minimal, and no evidence of cone death was detected. In the SD retina, the same photopic exposure had no measurable effects on death rates, OS length, or ERG responses in either rods or cones. Longer (7 days) photopic exposure reduced cone and rod OS length and ERG responses in SD, as well as P23H-3 retinas, but less severely than in the P23H-3 strain. Cones are damaged rapidly in the P23H-3 retina when rod damage is accelerated by raised ambient illumination. This close dependence of cone integrity on rod integrity contrasts with the life-long persistence of cone function in the scotopic reared P23H-3 rat. In humans suffering comparable photoreceptor dystrophies, the maintenance of steady, low ambient light may, by minimizing acute rod damage, optimize the function of surviving cones.

Twenty-four hours light exposure experiences in postpartum women and their 2–10-week-old infants: An intensive within-subject design pilot study

Background Adequate light exposure is critical for entraining circadian rhythms, regulating sleep–wake cycles, and maintaining optimal mood. Yet, few studies have reported normative data on light exposure experiences in postpartum women and young infants; none has examined the two simultaneously. Objectives The objective of this pilot study was to document the 24-h light exposure experiences in postpartum women and their infants. Design An intensive within-subject design was employed. Settings The participant’s natural home environment. Participants Twenty-four healthy mother–infant pairs were recruited from the general community in Seattle, USA. Two mother–infant pairs did not have complete data, resulting in a final sample size of 22 (12 female infants). Methods Mothers and infants wore a monitor to continuously record illumination levels for 7 days. Data were aggregated within subject to calculate summary measures of illumination exposure. Circadian patterns of light were examined using cosinor analysis. Pearson correlation was used to examine the relation between maternal and infant light exposure. Results Mothers spent 71.13 ± 11.58% and infants spent 80.07 ± 8.27% of their daytime hours (defined as 06:00–21:59) in an illumination level <50 lux. Mean minutes >1000 lux per day was 54 ± 39 for mothers and 23 ± 18 for infants. Maternal and infant light exposure exhibited a modest circadian pattern and a strong correlation, both in the timing of peak illumination exposure ( r = 0.93, p < 0.01) and in the level of light exposure ( r = 0.70 ± 0.07). Conclusions Postpartum women and infants experience low ambient light levels with short periods of bright light during the day. Whether this level of light is sufficient for optimal postpartum mood and infant circadian entrainment warrants further investigation. If higher levels of light were indeed necessary for postpartum women and young infants, increasing ambient light levels through the use of natural sunlight (i.e., walking outdoors) could be a simple and economic nursing intervention. The strong pattern synchrony between maternal and infant light exposure suggests that mothers play the primary role in providing a lighting environment suitable for infants to synchronize their circadian rhythms to a 24-h day.

A systems biology approach identifies the biochemical mechanisms regulating monoterpenoid essential oil composition in peppermint

The integration of mathematical modeling and experimental testing is emerging as a powerful approach for improving our understanding of the regulation of metabolic pathways. In this study, we report on the development of a kinetic mathematical model that accurately simulates the developmental patterns of monoterpenoid essential oil accumulation in peppermint (Mentha x piperita). This model was then used to evaluate the biochemical processes underlying experimentally determined changes in the monoterpene pathway under low ambient-light intensities, which led to an accumulation of the branchpoint intermediate (+)-pulegone and the side product (+)-menthofuran. Our simulations indicated that the environmentally regulated changes in monoterpene profiles could only be explained when, in addition to effects on biosynthetic enzyme activities, as yet unidentified inhibitory effects of (+)-menthofuran on the branchpoint enzyme pulegone reductase (PR) were assumed. Subsequent in vitro analyses with recombinant protein confirmed that (+)-menthofuran acts as a weak competitive inhibitor of PR (K(i) = 300 muM). To evaluate whether the intracellular concentration of (+)-menthofuran was high enough for PR inhibition in vivo, we isolated essential oil-synthesizing secretory cells from peppermint leaves and subjected them to steam distillations. When peppermint plants were grown under low-light conditions, (+)-menthofuran was selectively retained in secretory cells and accumulated to very high levels (up to 20 mM), whereas under regular growth conditions, (+)-menthofuran levels remained very low (<400 muM). These results illustrate the utility of iterative cycles of mathematical modeling and experimental testing to elucidate the mechanisms controlling flux through metabolic pathways.

A review of flatfish behavior relative to trawls

Trawls harness the innate avoidance behavior of fish to affect their capture. As such, effective bycatch reduction relies, in part, upon knowledge of behavioral differences between target and non-target species. The behavior of flatfish during herding, net entry and passage through trawls differs substantially from that of many roundfish. These differences result from the unique body morphology of flatfish and the constraints this morphology places upon their natural predator avoidance and evasion tactics. Paramount, in this regard, is the intimate association between flatfish and the seafloor. Flatfish utilize a detection minimization strategy that combines burial, highly evolved cryptic capabilities and low activity. Additionally, the maximum sustained swimming speeds and endurance of flatfishes are low compared to most roundfish. As a result, flatfish typically respond to trawl ground-gear at shorter distances, remain closer to the seafloor during herding and herd in the net mouth for a shorter time, prior to net entry, than roundfish. As is the case for roundfish species, light and temperature influence flatfish reactivity and herding behavior. At low ambient light levels herding behavior in flatfish breaks down, as fish initially respond to ground-gear by rising off the bottom, which removes them from the ground-gear's zone of influence. Similarly, at low temperatures some flatfish display reduced herding. Differences in behavior between flatfish and roundfish have spurred development of selective flatfish trawls, with low rise head ropes and/or open or large mesh intermediates that allow rising roundfish to exit the net opening, while flatfish remain close to the net floor, passing into the net and back to the codend. Lastly, a conceptual design for a counter-herding device is presented, which takes advantage of the longer reactive distances of roundfish, and their tendency to herd farther of the seafloor, thereby allowing them to be herded out of the path of the net, while not influencing the normal inward herding of flatfish.

Casualty Collection in Mass-Casualty Incidents: A Better Method for Finding Proverbial Needles in a Haystack

Mass-casualty incidents (MCIs) are on the rise. The ability to locate, identify, and triage patients quickly and efficiently results in better patient outcomes. Poor lighting due to time of day, inclement weather, and power outages can make locating patients difficult. Efficient methods of locating patients allow for quicker transport to definitive care. The objective of this study was to evaluate the methods currently used in mass-casualty collection, and to determine whether the use of the Simple Triage and Rapid Treatment (START) triage tag system can be improved by using easily discernable tags (glow sticks) in conjunction with the standard triage tags. Numerous drills were performed utilizing the START triage method. In Trial A, patients were identified with the triage tags only. In Trial B, patients were identified using triage tags and glow sticks. Four rounds of triage drills were performed in low ambient light for each Trial, and the differences in casualty collection times were compared. Casualty relocation and collection times were considerably shorter in the trials that utilized both the glow sticks and triage tags. An average of 2.58 minutes (31.75%) were saved during the casualty collections. In addition, fewer patient errors occurred during the trials in which the glow sticks were used. Between the four rounds, an average of four patient errors occurred during the trials that utilized the triage tags. However, there was an average of only one patient error for the drills when participants utilized both the triage tags and the glow sticks. The use of the highly visible glow sticks, in conjunction with the START triage tags, allowed for more rapid and accurate casualty collection in suboptimal lighting. The use of the glow sticks made it easier to relocate previously triaged patients and arrange for expeditious transport to definitive care. In addition, the glow sticks reduced the number of patient errors. Most importantly, there was a significant reduction in the number of patients that initially were triaged via the START method, but were overlooked during casualty collection and transport.

Effects of colour vision phenotype on insect capture by a free-ranging population of white-faced capuchins, Cebus capucinus

Unlike most eutherian mammals, which have dichromatic (two-colour) vision, most platyrrhine primate species have polymorphic colour vision. This unique characteristic is enabled via multiple alleles for a midto long-wavelength-sensitive (M/LWS), single-locus opsin gene on the X chromosome. In combination with the autosomal opsin common to most vertebrates, this arrangement provides heterozygous females with trichromatic (three-colour) vision, whereas homozygous females and males are dichromats. Trichromatic vision enables visual differentiation among longer-wavelength colours, such as red, orange, yellow and green. Currently, many researchers attribute the evolution and maintenance of polymorphic colour vision to trichromat (¼ heterozygote) advantage. However, dichromacy may be more suited for achromatic tasks, such as penetrating colour camouflage, especially under low-light conditions. We evaluated whether dichromatic capuchin monkeys (Cebus capucinus) were more efficient than trichromatic monkeys at capturing camouflaged and noncamouflaged insects. Through faecal DNA analysis, we determined the genotypes of the M/LWS opsins for 34 capuchins in two groups inhabiting Santa Rosa National Park, Costa Rica. Dichromatic monkeys were more efficient at detecting camouflaged, surface-dwelling insects, especially under conditions of low ambient light. However, unexpectedly, trichromats were more efficient in extracting embedded, noncamouflaged insects from substrates. To our knowledge, this is the first study to document a foraging advantage to dichromatic monkeys in the wild. Our findings show that there is a lack of heterozygote advantage in foraging for surface-dwelling insects and therefore indicate that this mechanism may not be the sole driving force maintaining polymorphic colour vision in this population.

Rapid light-response curves of chlorophyll fluorescence in microalgae: relationship to steady-state light curves and non-photochemical quenching in benthic diatom-dominated assemblages

Rapid light-response curves (RLC) of variable chlorophyll fluorescence were measured on estuarine benthic microalgae with the purpose of characterising its response to changes in ambient light, and of investigating the relationship to steady-state light-response curves (LC). The response of RLCs to changes in ambient light (E, defined as the irradiance level to which a sample is acclimated to prior to the start of the RLC) was characterised by constructing light-response curves for the RLC parameters alpha (RLC), the initial slope, ETR(m,RLC), the maximum relative electron transport rate, and E (k,RLC), the light-saturation parameter. Measurements were carried out on diatom-dominated suspensions of benthic microalgae and RLC and LC parameters were compared for a wide range of ambient light conditions, time of day, season and sample taxonomic composition. The photoresponse of RLC parameters was typically bi-phasic, consisting of an initial increase of all parameters under low ambient light (E < 21-181 micromol m(-2) s(-1)), and of a phase during which alpha (RLC) decreased significantly with E, and the increase of ETR(m,RLC) and E (k,RLC) was attenuated. The relationship between RLC and LC parameters was dependent on ambient irradiance, with significant correlations being found between alpha (RLC) and alpha, and between ETR(m,RLC) and ETR(m), for samples acclimated to low and to high ambient irradiances, respectively. The decline of alpha (RLC) under high light (Deltaalpha (RLC)) was strongly correlated (P < 0.001 in all cases) with the level of non-photochemical quenching (NPQ) measured before each RLC. These results indicate the possibility of using RLCs to characterise the steady-state photoacclimation status of a sample, by estimating the LC parameter E (k), and to trace short-term changes in NPQ levels without dark incubation.

Measuring the ability to stay awake: role of motivation

The measurement of daytime sleepiness and alertness is based upon the concepts of physiologic and manifest sleepiness [1]. Physiologic sleepiness is the tendency to fall asleep in the absence of alerting factors and is measured by the multiple sleep latency test (MSLT). Manifest sleepiness changes on a moment-to-moment basis and is determined by factors such as light, noise, motivation, hunger, and recumbency. Manifest sleepiness or the ability of an individual to stay awake under soporific conditions may be more clinically relevant and may be a more important measure for situations in which alertness is warranted, such as driving or operating heavy machinery. The maintenance of wakefulness test (MWT) was developed to measure an individual’s ability to stay awake [2] and is performed with the individual sitting in a room with low ambient light. It is believed that the MWT is a valid test in that the sleep latency on the MWT is shorter for subjects with sleep disorders compared to normal controls and increases with treatment (see an excellent recent review for details [3]. Recent guidelines state that the MWT “may be used to assess an individual’s ability to remain awake when his/her inability to remain awake constitutes a public or personal safety issue” [4]. Given that motivation is considered a determinant of an individual’s ability to stay awake in certain situations, the influence of motivation on the sleep latency measured on the MWT needs to be systematically studied, especially if the test to be used is a test that determines if an individual can remain licensed to drive. Individuals who face loss of license or employment could theoretically manipulate the test, resulting in a normal sleep latency. The study by Shreter et al. [5] published in this issue of Sleep & Breathing sheds light on this issue. The authors investigated a group of patients, the majority with untreated sleepdisordered breathing, who had been referred by the National Council for Driving Safety in Israel for evaluation of daytime sleepiness. All patients were referred knowing that if they “failed” the test their driving license would not renewed. The authors hypothesized that this would be sufficient motivation to maintain wakefulness on the 20-min protocol MWT. Confirming their hypothesis, only 5 out of 54 patients fell asleep on any of the MWT trials. Of the 21 patients with severe untreated obstructive sleep apnea, only one fell asleep during the MWT. The authors conclude that motivation profoundly affects the ability of an individual to stay awake on the MWT. There was one previous study that investigated the influence of motivation on sleep latency in the MWT [6]. In this study, the authors found that motivated normal subjects could decrease their sleep latency (fall asleep faster) on the MWT but were unable to increase their sleep latency (stay awake longer). The authors concluded that the MWT is an excellent choice for measuring daytime alertness as it is minimally affected by a participant’s motivation. There are several methodological differences between the two studies that explain differing results. First, in the study of Bonnet and Arand [6], the subjects served as their own controls. Unfortunately, there is no control group in the Shreter et al. study [5]. The inclusion of patients matched for age, gender, and presence/severity of sleep-disordered breathing but without motivation to “pass the test” (driving license/ employment not at risk) would have increased the reliability of the results. If the control group had an increased rate of falling asleep and a shorter sleep latency on the MWT, then motivation would clearly have been the major reason for the lack of sleep in the at-risk patients. Without the control Sleep Breath (2006) 10:171–172 DOI 10.1007/s11325-006-0071-0

Cost/benefit analysis of group and solitary resting in the cowtail stingray, Pastinachus sephen

Unless a safe refuge is found where predation threats are negligible, resting poses risks for many animals, necessitating risk management strategies. The adult cowtail stingray (Pastinachus sephen) of Shark Bay, Western Australia, is a solitarily foraging animal that facultatively groups when resting on shallow, inshore sand flats. We hypothesized that environmental conditions influence the propensity of cowtails to group due to the limited ability to detect predators visually in certain conditions. We then explored the possible benefits of grouping, such as bodily protection, early warning, and predator confusion, in conjunction with potential grouping costs, such as increased interference when initiating flight and decreased escape speeds. Our study revealed that in poor underwater visibility (due to turbidity and/or low ambient light levels), cowtails primarily rest in small groups (three rays). Tests of flight initiation distance to a mock predator demonstrated that solitary cowtail escape distances are significantly shorter in poor than in good underwater visibility conditions. As to grouping benefits, filmed boat transects revealed that cowtails most often arrange themselves in a rosette position, possibly as a means to protect their bodies and expose their tails. The first cowtail in a group initiates flight to a mock predator at a significantly greater distance than a solitary cowtail, and grouped cowtails escape an approaching boat in a significantly more cohesive manner than a simulated group of escaping individual rays. Grouped cowtails exhibit behaviors that would impede immediate flight after detection. As a result, grouped rays escape a boat at significantly slower speeds than solitary cowtails. Results from this study demonstrate that the interplay between costs and benefits of grouped and solitary resting under differing environmental conditions is driven by differences in perceived predation risk and ultimately reflected in the facultative grouping behavior of this species. Key words: antipredator behavior, facultative grouping, group resting, Pastinachus sephen, perceived predation risk, stingrays. [Behav Ecol]

Effect of monitor luminance and ambient light on observer performance in soft-copy reading of digital chest radiographs.

To examine the combined effects of monitor luminance and ambient light on observer performance for detecting abnormalities in a soft-copy interpretation of digital chest radiographs. A total of 254 digital chest radiographs were displayed on a high-resolution cathode ray tube monitor at three luminance levels (25, 50, and 100 foot-lamberts) under three ambient light levels (0, 50, and 460 lux). Six chest radiologists reviewed each image in nine modes of combined luminance and ambient light. The observers were allowed to adjust the window width and level of the soft-copy images. The abnormalities included nodule, pneumothorax, and interstitial disease. Observer performance was analyzed in terms of the receiver operating characteristics. The observers reported their subjective level of visual fatigue with each viewing mode. A statistical test was conducted for each of the abnormalities and for fatigue score by using repeated-measures two-way analysis of variance with an interaction. The detection of nodules was the only reading that was affected by the ambient light with a statistically significant difference (P <.05). Otherwise, observer performance for detecting a nodule, pneumothorax, and interstitial disease was not significantly different in the nine-mode comparison. There was no evidence that the luminance of the monitors was related to the ambient light for any of the abnormalities. The fatigue score showed a statistically significant difference due to both the luminance and ambient light. When adequate window width and level are applied to soft-copy images, the primary diagnosis with chest radiographs on the monitor is unlikely to be affected under low ambient light and a monitor luminance of 25 foot-lamberts or more.

Pollen and spores in marine Cretaceous/Tertiary boundary sediments at mid‐Waipara River, North Canterbury, New Zealand

Terrestrial pollen and spores in late Maastrichtian to early Paleocene marine strata at mid‐Waipara, New Zealand, permit reconstruction of contemporary vegetation and paleoclimates. During the latest Cretaceous, spore‐pollen assemblages reflect a temperate rainforest with a prominent podocarp and tree ferns component, angiosperm pollen being mainly represented by Nothofagus and Proteaceae. Disruption of the vegetation at the Cretaceous/Tertiary (K/T) boundary is recorded by an increase in fern spores, reduction in gymnosperm pollen, and temporary loss of angiosperm pollen both in mid Waipara and in the terrestrial sections of Moody Creek Mine and Compressor Creek. Following an interval of fern dominance, gymnosperms and later angiosperms return to the palynological record. The floral turnover at the K/T boundary is comparable to palynological records from North America and Japan, indicating that disruption of vegetation was global. Fern dominance is estimated to have lasted several thousands of years, based on foraminiferal biostratigraphy of immediate post‐K/T boundary strata. This is orders of magnitude greater than seen in normal seral successions following deforestation. We suggest that the observed vegetation succession is due to a prolonged period of low ambient light levels, sufficient for photosynthesis but favouring plants already adapted to these levels (such as forest ground stratum), accompanied by a moderate temperature and moisture regime.

Role of melatonin in the regulation of human circadian rhythms and sleep.

The circadian rhythm of pineal melatonin is the best marker of internal time under low ambient light levels. The endogenous melatonin rhythm exhibits a close association with the endogenous circadian component of the sleep propensity rhythm. This has led to the idea that melatonin is an internal sleep "facilitator" in humans, and therefore useful in the treatment of insomnia and the readjustment of circadian rhythms. There is evidence that administration of melatonin is able: (i) to induce sleep when the homeostatic drive to sleep is insufficient; (ii) to inhibit the drive for wakefulness emanating from the circadian pacemaker; and (iii) induce phase shifts in the circadian clock such that the circadian phase of increased sleep propensity occurs at a new, desired time. Therefore, exogenous melatonin can act as soporific agent, a chronohypnotic, and/or a chronobiotic. We describe the role of melatonin in the regulation of sleep, and the use of exogenous melatonin to treat sleep or circadian rhythm disorders.

Ecological stoichiometry in the microbial food web: a test of the light:nutrient hypothesis

The 'light:nutrient hypothesis' (LNH) states that the importance of the microbial food web relative to grazing impacts by macrozooplankton and the nature of the relationship between algae and bacteria (competition or commensalism) are affected by the balance of light and nutrients experienced by phytoplankton. We tested this hypothesis in field enclosures by manipulating irradi- ance and nutrient supply in a P-limited lake in Ontario, Canada. Shading and P-enrichment had little effect on standing biomass of small suspended particles (<1 µm) but both decreased C:P ratio in this size fraction. P-fertilization had no effect on algal biomass or bacterial abundance but shading signif- icantly lowered algal biomass and the ratio of algal biomass to bacterial abundance. Shading had no effect on heterotrophic nanoflagellates (HNF) but HNF abundance declined strongly with P-enrich- ment under both shaded and unshaded conditions, coincident with large increases in macrozoo- plankton biomass that accompanied P-fertilization. Shading and nutrient enrichment also affected resource limitation as indicated by dilution bioassays. Increased algal light limitation in the enclo- sures was associated with lower seston C:P ratio, as expected under the LNH. In addition, the C:P ratio of new seston produced in bioassay bottles was also affected by enclosure treatment; unshaded enclosures generally produced seston with moderately high C:P ratio while shaded enclosures pro- duced new seston at low C:P under low ambient light but at very high C:P ratio when algae were incubated at higher light. Our data provide support for some aspects of the LNH, including predicted impacts on the microbial loop and on resource limitations and C:P stoichiometry. However, some responses were not consistent with the LNH, indicating that the hypothesis needs to be modified to incorporate potential indirect effects.