Photophobic responses of calanoid copepods: possible adaptive value

A genual pattern of photophobic responses has been observedwhich differs for calanoid copepods from freshwater, estuarineand oceanic environments. Using a video-computer system formotion analysis, the photophobic responses of light and darkadapted calanoid copepods were compared. Dark-adapted copepodswere exposed to 600 ms flashes of dim blue light at 5 s intervalswhich simulated the flashes of biolumines-cent marine zooplankton.Light-adapted copepods were exposed to 600 ms intervals of darknessat 5 s intervals to simulate the shadows of organisms passingoverhead. Four species of coastal marine copepods (Acartia hudsonica,Centropages hamatus, Pseudocalanus minutus and Temora longicornis)all showed photophobic responses to both flashes and shadows.These responses may have adaptive value to the copepods sincethey live in an environment with predators that are bioluminescentat night and cast shadows on their prey during the day (e.g.ctenophores and cnidarian medusae). Two species of oceanic copepods(Euchaeta marina, Pleuromamma abdominalis) showed strong photophobicresponses to flashes but no response to shadows. This may correspondto the abundance of bioluminescent predators on copepods inthe oceanic environment (fish, ctenophores, siphonophores, etc.)and their lack of exposure to the shadows of predators, sinceboth these species are rarely found in the euphoric zone duringthe day. Two species of freshwater copepods (Diaptomus sanguineus,Epishwa massachusettsensis) showed no similar photophobic responseto flashes of light. This lack of startle response may relateto the lack of bioluminescence in the freshwater environment.Freshwater copepods showed a weak photophobic response to shadows.The adaptive value of this behavior is unclear, however, sincethe responses seem to be too weak to function for escape, andthe dominant predators large enough to cast shadows (fish) tendto approach their prey laterally. ¹Present address: Marine Science Institute, University of Texasat Austin, Port Aransas, TX 78373–1267, USA     

Creating Eclipses: Using Scale Models to Explore How Eclipses Happen

The importance of using proportional scaled models in teaching about eclipses to elementary- and middle-level students is presented in this article. The authors illustrate how using creative models to display the basic concepts of shadows, scale, and perspective can foster a deeper understanding of how eclipses occur. Three innovative, easy-to-construct, scaled models are described as effective tools to enhance students’ understanding of eclipses. The models include space perspective on cast shadows, Earth perspective on solar eclipses, and the Moon's orbital plane around Earth.     

Dealing with Illumination in Visual Scenes: Effects of Ageing and Alzheimer's Disease

Various visual functions decline in ageing and even more so in patients with Alzheimer''s disease (AD). Here we investigated whether the complex visual processes involved in ignoring illumination-related variability (specifically, cast shadows) in visual scenes may also be compromised. Participants searched for a discrepant target among items which appeared as posts with shadows cast by light-from-above when upright, but as angled objects when inverted. As in earlier reports, young participants gave slower responses with upright than inverted displays when the shadow-like part was dark but not white (control condition). This is consistent with visual processing mechanisms making shadows difficult to perceive, presumably to assist object recognition under varied illumination. Contrary to predictions, this interaction of “shadow” colour with item orientation was maintained in healthy older and AD groups. Thus, the processing mechanisms which assist complex light-independent object identification appear to be robust to the effects of both ageing and AD. Importantly, this means that the complexity of a function does not necessarily determine its vulnerability to age- or AD-related decline.We also report slower responses to dark than light “shadows” of either orientation in both ageing and AD, in keeping with increasing light scatter in the ageing eye. Rather curiously, AD patients showed further slowed responses to “shadows” of either colour at the bottom than the top of items as if they applied shadow-specific rules to non-shadow conditions. This suggests that in AD, shadow-processing mechanisms, while preserved, might be applied in a less selective way.     

Chem-Ray: A molecular graphics program featuring an umbra and penumbra shadowing routine

Chem-Ray, new molecular graphics program, utilizes a combination of standard algorithms developed for molecular systems as well as various ray casting techniques to produce highly realistic images on inexpensive raster terminals. The program produces images of space-filling, ball and stick or stick models derived from a user-supplied co-ordinate list. The most notable new feature of Chem-Ray is a simple, yet effective, algorithm for the improved treatment of shadows within a molecule. This new algorithm is based upon a calculation of a light pyramid at each point under examination. Intersections of various objects with this light pyramid will decrease the percentage of the light that can reach the point. If the entire cross-section is blocked, the point will be in the umbra of the shadow; if only a portion of the light is blocked, the point will be in the penumbra of the shadow.     

Introducing an inquiry-based experiment-integrated science game for elementary students: the shadow races game

Abstract

This article introduces a science game which can be used for innovative teaching and as an assessment tool. The Shadow Races Game is designed for first and second grade students to learn the phenomenon of shadow through inquiry-based activities and questions that require the children to apply inferences from those activities. In this amusing board game, students will discover the relationship between light, objects and shadows using familiar objects.     

The effect of light and darkness on the production of cercariae of Schistosoma haematobium from Bulinus globosus

The cercariae of Schistosoma haematobium showed a diurnal periodicity of emergence from Bulinus globosus in a twelve hour light/dark cycle. Peak emission occurred at 11.00 hrs with a smaller peak at 20.00 hrs, following the start of the period of darkness. In continuous illumination this second peak was not seen, indicating that only the morning peak is circadian in origin. The evening peak occurs in response to dark treatment and can be produced by periods of darkness ranging from eight seconds to one hour. The longer the period of dark treatment the longer the rise in output is maintained on return to light conditions. Subjection of snails to periods of dark treatment during the normal light period caused a reduction in the evening peak with the largest effect seen following the longest period of darkness. An increased output of cercariae was seen following fifteen minutes exposure to a range of light intensities, the largest increase occurring at 10,000 and 7000 lux and complete darkness. The rapidity of this reaction to variations in light intensity suggests that the cercariae of S. haematobium are showing emergence in response to shadows.     

Reactions to shadows in captive Guinea baboons

The occurrence of reactions to shadows is reported in a captive group of Guinea baboons (Papio papio). While poorly defined shadows did not induce specific responses, baboon-like silhouettes cast on walls elicited aggressive responses. There was no evidence that baboons recognize one’s own shadow or are even aware that shadows have a physical referent.     

What, if anything, is the adaptive function of countershading?

Countershading, the gradation of colour from dark on the dorsum to light on the ventrum, is generally considered to have the effect of making organisms difficult to detect. The mechanism that facilitates this form of crypsis is often considered to be concealment of shadows cast on the body of the animal. We review the current empirical evidence for the cryptic function of countershading and for the mechanism underlying it. We argue that there is no conclusive evidence that countershading per se provides any selective advantage in terrestrial or aerial environments. However, the highly refined adaptations of some marine organisms to match the different background light conditions against which they are set when viewed from different aspects strongly suggest an adaptive advantage to countershading in these environments. In none of the cases discussed in this review was the conventional explanation of self-shadow concealment a more plausible explanation for countershading than the alternative explanation that the dorsum and ventrum experience different selection pressures (often associated with background matching).     

On the role of blue shadows in the visual behaviour of tsetse flies

Tsetse flies (Glossina spp.), the vector for African trypanosomiasis, are highly attracted by blue and black surfaces. This phototactic behaviour has long been exploited to trap tsetse flies as one measure in the control of African trypanosomiasis. However, why blue and black are so attractive for tsetse flies is still unknown. We propose that the combination of blue and black is attractive for many Glossina species because when searching for a shady resting place to pass the day, the flies are probably guided by the blueness and darkness of daytime shadows. In contrast to people's experience that daytime shadows are colourless, actually on a sunny day all shadows are tinted bluish by the scattered blue skylight.     

Estimate of the seed shadow created by the Asiatic black bear Ursus thibetanus and its characteristics as a seed disperser in Japanese cool‐temperate forest

We estimated the seed shadow created by the Asiatic black bear Ursus thibetanus in order to evaluate the bears effectiveness as a seed disperser. We combined data from bear movements, determined by GPS telemetry, with data from gut retention time (GRT). We estimated plant seed shadows in two ways: from direct movement data to give the actual seed shadow (ASS), and from cumulative movement data to give the potential seed shadow (PSS). The purpose of this study was to answer the following questions: (1) does GRT differ between seasons or in the size of contents? (2) Does seed shadow vary among sex, seasons, estimation method (ASS or PSS), and years? (3) Does the masting affect seed shadows? There were no differences in median GRT among seasons or seed dimensions. Combining these data, the seed shadows produced by long GRT (median; 15.2–19.7 hours, maximum; 44.0 hours) and large daily movements suggest that the bears effectively move 40% of the seeds they consume to a distance greater than 500 m from the parent tree and can potentially move the seeds up to a maximum distance of more than 22 000 m from the parent tree. The results also indicate that bears make complex seed shadows caused by multiple defecations and long periods of daily movement. In summary, PSS did not differ between sexes, but PSS can be expected to be larger in autumn than in summer of each year. ASS, however, can be expected to be larger in males than females, and to be larger in autumn than in summer. ASS may become especially large during a poor masting year as compared to good masting years. These results indicate that bears are potentially more effective seed dispersers during years of poor fruit production in autumn. The bears have longer seed shadows than other seed disperser and consequently may play a unique role in the maintenance and renewal of forest ecosystem.     

Dispersal mode,seed shadows,and colonization patterns

This review assesses the state of our knowledge about comparative seed shadows. Using data presently available in the literature, I compare the slopes (on a log-linear scale) of seed shadows for plants with different morphologically characterized modes of dispersal. The seeds of many species have no evident morphological adaptation for dispersal and seem to achieve only short-distance dispersal. Seed shadows for herbaceous species with devices for wind have flatter slopes and more distant modes and maxima than those of ballists, which in turn exceed those with no special devices. Seed shadows for wind-dispersed trees and shrubs had similar or steeper slopes than those for vertebrate-dispersed species in this sample. Species with poor mechanisms for dispersal in space only sometimes had the capacity for better dispersal in time (dormancy). Although some species exhibited seed shadows sufficiently steep to be predicted to colonize new-habitat in a front or phalanx pattern, actual colonization patterns must reflect many other factors.     

Features of incorporation of several antibiotics into erythrocyte ghosts--a system of targeted delivery of chemotherapeutic drugs

Features of incorporation of cefazolin, ampicillin, kanamycin and gentamicin into erythrocytic shadows in patients with abdominal diseases and apparently healthy persons during hypoosmotic hemolysis were studied. The highest percentage of kanamycin and gentamicin incorporation into the erythrocytic shadows was observed. The parameter of the antibiotic incorporation from the incubation fluid into the erythrocytic shadows depended on the antibiotic type and dose. Rather significant resistance of the erythrocytic carriers with incorporated gentamicin to possible desorption and excretion of the antibiotic from the shadows into the blood flow was revealed which made their use possible for target release of antibiotics in the liver.     

Which retinal and extra-retinal information is crucial for circular vection?

In contradistinction to conventional wisdom, we propose that retinal image slip of a visual scene (optokinetic pattern, OP) does not constitute the only crucial input for visually induced percepts of self-motion (vection). Instead, the hypothesis is investigated that there are three input factors: 1) OP retinal image slip, 2) motion of the ocular orbital shadows across the retinae, and 3) smooth pursuit eye movements (efference copy). To test this hypothesis, we visually induced percepts of sinusoidal rotatory self-motion (circular vection, CV) in the absence of vestibular stimulation. Subjects were presented with three concurrent stimuli: a large visual OP, a fixation point to be pursued with the eyes (both projected in superposition on a semi-circular screen), and a dark window frame placed close to the eyes to create artificial visual field boundaries that simulate ocular orbital rim boundary shadows, but which could be moved across the retinae independent from eye movements. In different combinations these stimuli were independently moved or kept stationary. When moved together (horizontally and sinusoidally around the subject's head), they did so in precise temporal synchrony at 0.05 Hz. The results show that the occurrence of CV requires retinal slip of the OP and/or relative motion between the orbital boundary shadows and the OP. On the other hand, CV does not develop when the two retinal slip signals equal each other (no relative motion) and concur with pursuit eye movements (as it is the case, e.g., when we follow with the eyes the motion of a target on a stationary visual scene). The findings were formalized in terms of a simulation model. In the model two signals coding relative motion between OP and head are fused and fed into the mechanism for CV, a visuo-oculomotor one, derived from OP retinal slip and eye movement efference copy, and a purely visual signal of relative motion between the orbital rims (head) and the OP. The latter signal is also used, together with a version of the oculomotor efference copy, for a mechanism that suppresses CV at a later stage of processing in conditions in which the retinal slip signals are self-generated by smooth pursuit eye movements.     

Proximate control of diel vertical migration in Phyllosoma larvae of the Caribbean spiny lobster Panulirus argus

Phyllosoma larvae of the spiny lobster Panulirus argus undergo diel vertical migration (DVM), in which they are at depth during the day and nearer the surface at night. This study determined the visual spectral sensitivity of Stage I larvae and investigated whether light plays a proximate role in DVM as an exogenous cue and as an entrainment cue for an endogenous rhythm in vertical migration. Under constant conditions, larvae have a circadian rhythm (24.5-h period) in vertical swimming that resulted in a twilight DVM pattern. The behavioral response spectrum and electroretinogram recording indicated two photoreceptor spectral classes with maxima at 360 and 486 nm. When stimulated in an apparatus that simulated the underwater angular light distribution, dark-adapted larvae showed only positive phototaxis, with a threshold intensity of 1.8 × 10(13) photons m(-2) s(-1) (3.0 × 10(-5) μmoles photons m(-2) s(-1)). They have an avoidance response to predator shadows in which they descend upon sudden decreases in light intensity of more than 69%. When stimulated with relative rates of decrease in light intensity as occur at sunset they ascended, whereas they descended upon relative rates of light intensity increase as occur at sunrise. Thus, the DVM pattern is controlled by both an endogenous circadian rhythm in swimming and behavioral responses to light at sunrise and sunset.     

Convergence of a cryptic saddle pattern in benthic freshwater fishes

Synopsis Many North American stream fishes have a similar color pattern of four dark saddles against a light background. An interesting feature of the pattern, in addition to its widespread taxonomic distribution, is its consistent configuration. The interval between the first and second saddle is usually the largest, and the last (third) interval is the smallest. All saddled North American freshwater fishes live on uneven, rocky substrates, and nearly all live in flowing water. It is hypothesized that these fishes achieve crypsis through disruptive coloration; the light spaces between the saddles mimic rocks and the dark saddles appear as shadows or gaps between rocks. Saddles are spaced unevenly because rocks in streams are a mixture of sizes; a fish that mimics a series of rocks of similar sizes is more conspicuous than one that mimics rocks of different sizes. The placement of saddles was measured on five North American species. In four of five North American species measured (a sculpin and three darters), the longest spaces are towards the head where the body is also the widest, this is thought to enhance crypsis because pieces of gravel tend to be round or square. In the madtom, the saddle pattern tends more towards even spacing. The madtom may not rely on camouflage to the same extent as other species examined because of decreased predation pressure associated with being nocturnal and possessing sharp spines and venom glands.     

The Production of Histological Tracings Facilitated by Back-Lighted Projection

The projection apparatus is placed on the floor and tilted upward at an angle of about 30° so that the image is formed on a sheet of rigid, transparent plastic. This sheet is supported by a frame held between two tables and aligned so that it is perpendicular to the axis of the projection beam. The paper for tracing the image is placed on the side of the plastic sheet opposite the projection apparatus. Thus, the operator is able to make the tracing of the image without annoyance by heat from the light source or encumbrance from shadows of the hand and pencil cast on the image.     

Disseminated <Emphasis Type="Italic">Penicillium Marneffei</Emphasis> Infection in an SLE Patient: A Case Report and Literature Review

Penicillium marneffei is an important opportunistic pathogen in Southeast Asia in HIV-positive individuals, but it rarely infects non-HIV ones. Four SLE patients with disseminated penicilliosis had been previously reported out of which 3 died. We describe a 46-year-old Chinese woman who had a 10 years history of SLE, associated with disseminated Penicillium marneffei infection, which presented as fever, subcutaneous masses, and fine nodular shadows disseminated over lung fields. She was initially misdiagnosed as miliary tuberculosis and panniculitis that did not respond to anti-tubercular drugs and prednisone. The correct diagnosis was finally made by histopathology and tissue culture and also culture from exudate. She responded well to antifungal therapy in the form of intravenous amphotericin B for 2 weeks followed by itraconazole plus fluconazole. The cutaneous lesions were cured leaving behind scars by secondary suture after times of epluchage, and the fine nodular shadows over lungs disappeared finally. She had no recurrence on 8 months of follow-up. We also review the literature on this topic.     

A new technique to gather 3‐D spatial information using a single camera

A new technique using a single camera and shadows to determine 3‐D spatial positions of fishes in the laboratory is described. The apparatus consisted of a large aquarium (2·0 × 1·5 × 0·4 m), a wide‐angle camera mounted above and two light sources to cast shadows to either side of the fish. Using image analysis and vector mathematics, aquarium objects were plotted within 1·5 cm of their actual location along the x ‐, y ‐ and z ‐axis. The technique was also successful in quantifying changes in 3‐D spatial pattern of juvenile fish, Atlantic cod Gadus morhua (7·4–8·6 cm standard length, L _S) and cohabitant piscivorous shorthorned sculpin Myoxocephalus scorpinus (12·0–25·8 cm L _S), at these same viewing fields. The new technique should have a wide application, largely because it is potentially less expensive, laborious and invasive than alternative methods for determining 3‐D positions of fishes.     

The Judicious Use of Instructional Technology in Science Education

It is natural to study astronomy outdoors, but it is not quite as natural to study astronomy during the daytime. This lesson uses the Earth's closest star as a subject of study within the schoolyard. The importance of the rising sun is combined with hands-on inquiry in which students explore the properties of shadows. Students (a) complete a modified Know and Need to Know (KNK) chart about shadows, (b) complete task cards to help direct their inquiry, (c) develop two rules about shadows and the sun, and (d) reflect upon the experience through a writing assignment.     

Neural control of behavioural choice in juvenile crayfish

Natural selection leads to behavioural choices that increase the animal''s fitness. The neuronal mechanisms underlying behavioural choice are still elusive and empirical evidence connecting neural circuit activation to adaptive behavioural output is sparse.We exposed foraging juvenile crayfish to approaching shadows of different velocities and found that slow-moving shadows predominantly activated a pair of giant interneurons, which mediate tail-flips that thrust the animals backwards and away from the approaching threat. Tail-flips also moved the animals farther away from an expected food source, and crayfish defaulted to freezing behaviour when faced with fast-approaching shadows. Under these conditions, tail-flipping, an ineffective and costly escape strategy was suppressed in favour of freezing, a more beneficial choice. The decision to freeze also dominated in the presence of a more desirable resource; however, the increased incentive was less effective in suppressing tail-flipping when paired with slow-moving visual stimuli that reliably evoked tail-flips in most animals. Together this suggests that crayfish make value-based decisions by weighing the costs and benefits of different behavioural options, and they select adaptive behavioural output based on the activation patterns of identifiable neural circuits.