COVID-19 and “natural” experiments arising from physical distancing: a hypothetical case study from chronobiology

ABSTRACT

With countless “natural” experiments triggered by the COVID-19-associated physical distancing, one key question comes from chronobiology: “When confined to homes, how does the reduced exposure to natural daylight arising from the interruption of usual outdoor activities plus lost temporal organization ordinarily provided from workplaces and schools affect the circadian timing system (the internal 24 h clock) and, consequently, health of children and adults of all ages?” Herein, we discuss some ethical and scientific facets of exploring such natural experiments by offering a hypothetical case study of circadian biology.     

The anatomical basis of sexual dichromatism in non-iridescent ultraviolet-blue structural coloration of feathers

Despite extensive research on the evolution of avian dichromatism, the anatomical bases for differences between the sexes in species with structurally coloured plumage remain largely unknown. Using full‐spectrum spectrometry and transmission electron microscopy, we compared the colour and morphology of rump feathers of male and female eastern bluebirds (Sialia sialis). The ultraviolet (UV)‐blue feather colour in this species is caused by coherent scattering of light within the medullary ‘spongy layer’ of feather barbs. This spongy layer lies beneath a keratin cortex and on top of a layer of melanin granules that surround a hollow central vacuole. Irregularly shaped electron‐dense regions are present within the cortex. Male and female S. sialis differed substantially in their plumage colour and feather structure. A backwards logistic regression predicted sex with 100% accuracy using the colour variables brightness, UV‐violet (UV‐V) chroma and spectral saturation. A second backwards logistical regression predicted sex with 100% accuracy using relative cortex area and size of air spaces. Thus, S. sialis are dimorphic both in colour and in the structures causing this colour. Multiple regression analyses using data pooled from both sexes indicated that multiple features of feather barb structure contributed to colour variation in complex ways. Brightness was negatively related to the relative surface area of cortex in barb cross‐sections. Hue was positively related and UV‐V chroma was negatively related to the distance between scattering elements (i.e. keratin rods and air spaces) in the spongy layer. In contrast, hue was negatively related and UV‐V chroma was positively related to the thickness of the spongy layer. UV‐V chroma was also negatively related to the relative area of electron‐dense regions in the cortex. Spectral saturation was negatively related to the distance between scatterers and the standard error of the size of air spaces. These results suggest that the dimensions of spongy‐layer elements are critical to colour production, but that UV‐blue coloration can also be modified by the cortex and the thickness of the spongy layer. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84 , 259–271.     

The influence of the two different light intensities duringthe daytime on the colon motility in patients with irritable bowel syndrome (IBS): a preliminary report

Irritable bowel syndrome (IBS) is the most frequent functional disorder of the gastrointestinal tract, with great economical impact. The etiology and pathogenesis of the disease are unclear. Among patients seeking medical attention for IBS, 70 - 90% have psychiatric co-morbidity, most commonly major depression. In this study we test the influence of bright light on colon motility and subjectively felt symptoms. Eight IBS patients participated in the experiment. The passage rate was evaluated twice for every person: (1) after three days of exposure to bright light -3000 lux (from 8:00 to 18:00), (2) after three days exposure to dim light -100 lux (from 8:00 to 18:00). The comparison of colonic time in IBS patients point to differences in the elimination of markers, depending on experimental light conditions. After bright light conditions a tendency is observed to slower elimination of markers in the IBS-diarrhoea patients, and to a quicker elimination in the IBS-constipated patients. According to subjective feeling, all IBS patients reported an improvement in bowel function and relief of pain after bright but not after dim light application. Results of this preliminary study suggest that phototherapy might be a valuable addition to the conventional treatment of IBS.     

Photothermal model of plant development

The development of plants depends on the photoperiod length, light intensity, temperature, and length of light day integral. The reaction of a plant to the day length or daily light integral can depend on both the range of studied light intensities and photoperiod. Based on the data concerning the effects of light and thermal integrals on the developmental rate of plants of different photoperiodic groups, a photothermal model of plant development was proposed. The model was used to calculate the lengths of optimal photoperiods and ranges of daily temperature gradients ensuring the highest developmental rate of some plants, such as soybean, wheat, cucumber, and barley.     

FAILURE OF EXTRAOCULAR LIGHT TO FACILITATE CIRCADIAN RHYTHM REENTRAINMENT IN HUMANS

Although extraocular light can entrain the circadian rhythms of invertebrates and nonmammalian vertebrates, almost all studies show that the mammalian circadian system can only be affected by light to the eyes. The exception is a recent study by Campbell and Murphy that reported phase shifts in humans to bright light applied with fiber-optic pads behind the knees (popliteal region). We tested whether this extraocular light stimulus could accelerate the entrainment of circadian rhythms to a shift of the sleep schedule, as occurs in shift work or jet lag. In experiment 1, the sleep/dark episodes were delayed 8h from baseline for 2 days, and 3h light exposures were timed to occur before the temperature minimum to help delay circadian rhythms. There were three groups: (1) bright (about 13,000 lux) extraocular light from fiber-optic pads, (2) control (dim light, 10–20 lux), and (3) medium-intensity (about 1000 lux) ocular light from light boxes. In experiment 2, the sleep/dark episodes were inverted, and extraocular light was applied either before the temperature minimum to help delay circadian rhythms or after the temperature minimum to help advance rhythms. Circadian phase markers were the salivary dim light melatonin onset (DLMO) and the rectal temperature minimum. There was no evidence that the popliteal extraocular light had a phase-shifting effect in either experiment. Possible reasons for phase shifts in the Campbell and Murphy study and not the current study include the many differences between the protocols. In the current study, there was substantial sleep deprivation before the extraocular light was applied. There was a large shift in the sleep/dark schedule, rather than allowing subjects to sleep each day from midnight to noon, as in the Campbell and Murphy study. Also, when extraocular light was applied in the current protocol, subjects did not experience a change from sleeping to awake, a change in posture (from lying in bed to sitting in a chair), or a change in ocular light (from dark to dim light). Further research is necessary to determine the conditions under which extraocular light might produce phase shifts in human circadian rhythms. (Chronobiology International, 17(6), 807–826, 2000).     

A Personal Light-Treatment Device for Improving Sleep Quality in the Elderly: Dynamics of Nocturnal Melatonin Suppression at Two Exposure Levels

Light treatment has been used as a non-pharmacological tool to help mitigate poor sleep quality frequently found in older people. In order to increase compliance to non-pharmacological light treatments, new, more efficacious light-delivery systems need to be developed. A prototype personal light-treatment device equipped with low brightness blue light-emitting diodes (LEDs) (peak wavelength near 470 nm) was tested for its effectiveness in suppressing nocturnal melatonin, a measure of circadian stimulation. Two levels of corneal irradiance were set to deliver two prescribed doses of circadian light exposure. Eleven older subjects, between 51 and 80 yrs of age who met the selection criteria, were exposed to a high and a low level of light for 90 min on separate nights from the personal light-treatment device. Blood and saliva samples were collected at prescribed times for subsequent melatonin assay. After 1 h of light exposure, the light-induced nocturnal melatonin suppression level was about 35% for the low-light level and about 60% for the high-light level. The higher level of blue light suppressed melatonin more quickly, to a greater extent over the course of the 90 min exposure period, and maintained suppression after 60 min. The constant exposure of the low-light level resulted in a decrease in nocturnal melatonin suppression for the last sampling time, whereas for the high-light level, suppression continued throughout the entire exposure period. The present study performed with healthy adults suggests that the tested personal light-treatment device might be a practical, comfortable, and effective way to deliver light treatment to those suffering from circadian sleep disorders; however, the acceptance and effectiveness of personal light-treatment devices by older people and by other segments of the population suffering from sleep disorders in a real-life situation need to be directly tested. (Author correspondence: figuem@rpi.edu)     

Factors influencing the attachment strength of Dreissena polymorpha (Bivalvia)

Abstract

The effects of several factors (shell length, exposure time, substratum orientation in space, illumination, temperature, conspecifics) upon the attachment strength (measured with a digital dynamometer) of the freshwater, gregarious bivalve Dreissena polymorpha were studied under laboratory conditions. A rapid increase in attachment strength was observed on resocart (a thermosetting polymer based on phenol-formaldehyde resin, with paper as filler) substrata during the first 4-d exposure, after which it stabilised at ca 1 N. The attachment strength increased also with mussel size. Mussel adhesion on variously oriented surfaces (vertical, upper horizontal and lower horizontal) was similar. Illumination inhibited attachment strength, as expected for a photophobic species, but only after a 2-d exposure. After 6 d, no effects of light were detected. Thus, illumination seemed to influence the attachment rate, rather than the final strength. The optimum temperature for mussel attachment was 20 – 25°C. At lower and higher temperatures (5 – 15°C and 30°C), their adhesion strength decreased. The presence of conspecifics stimulated mussel attachment strength.     

Clocks for the city: circadian differences between forest and city songbirds

To keep pace with progressing urbanization organisms must cope with extensive habitat change. Anthropogenic light and noise have modified differences between day and night, and may thereby interfere with circadian clocks. Urbanized species, such as birds, are known to advance their activity to early morning and night hours. We hypothesized that such modified activity patterns are reflected by properties of the endogenous circadian clock. Using automatic radio-telemetry, we tested this idea by comparing activity patterns of free-living forest and city European blackbirds (Turdus merula). We then recaptured the same individuals and recorded their activity under constant conditions. City birds started their activity earlier and had faster but less robust circadian oscillation of locomotor activity than forest conspecifics. Circadian period length predicted start of activity in the field, and this relationship was mainly explained by fast-paced and early-rising city birds. Although based on only two populations, our findings point to links between city life, chronotype and circadian phenotype in songbirds, and potentially in other organisms that colonize urban habitats, and highlight that urban environments can significantly modify biologically important rhythms in wild organisms.     

Light is a crucial signal for zoosporogenesis and gametogenesis in some green microalgae

Patterns of reproduction were investigated in some microalgal species of Chlorophyceae (Botryosphaerella sudetica, Neochloris aquatica, Neochloris vigensis, Bracteacoccus minor). Under continuous light, the microalgae reproduced asexually producing autospores. However, appropriate manipulation of external conditions led to a change in the reproduction pattern towards production of zoospores or gametes. Production of zoospores and gametes was inhibited by light; motile cells emerged when microalgae were cultivated in darkness. The period of dark treatment necessary for zoosporogenesis or gametogenesis differed substantially among species that were tested. Sexual reproduction was observed in Neochloris vigensis and Bracteacoccus minor, whose generative life cycle had not been previously reported. The morphology of motile cells, the mode of sexual reproduction, and the efficiency of both the production of motile stages and mating events, were investigated. In order to gain detailed insights into patterns of reproduction, Botryosphaerella sudetica was selected for investigation under different light treatments. Non-actinic red light applied in the early phase of dark cultivation (up to 2 h) suppressed both zoosporogenesis and gametogenesis. However, after a 3-h dark pre-treatment, red light treatment had no effect on zoosporogenesis or gametogenesis. In contrast, non-actinic blue light did not block zoosporogenesis or gametogenesis, regardless of the time of treatment. The possible role of a red-light photoreceptor in zoosporogenesis and gametogenesis is discussed.