THE PHOTOCHEMICAL BASIS OF ANIMAL HELIOTROPISM

1. Experiments on the heliotropic orientation of Limulus were made which confirmed Loeb''s photochemical theory of animal heliotropism proposed first in 1888 and 1889 in experiments on insects, and later in experiments on other forms of animals. 2. It is shown that these animals are oriented by light in such a way that the product I x t x cos α is the same for the symmetrical photosensitive elements of the eyes or the skin, where I is the intensity of the light, t the duration of illumination, and α the angle of incidence of the light at the surface element of the photosensitive organ. 3. When this equation holds, the products of decomposition by light must be the same in symmetrical elements of the eyes or skin, and the influence of these products of decomposition on the tension of symmetrical muscles of the locomotor organs of the animal must be the same. As a consequence the animal must move in the path of light, either to or from the source of light.     

Flower heliotropism in an alpine population of Ranunculus acris (Ranunculaceae): effects on flower temperature,insect visitation,and seed production

Some plants in arctic and alpine habitats have heliotropic flowers that track the sun. This results in a heating of the flower's interior, which may improve the possibilities for insect pollination and seed production. Here, I examine whether flower heliotropism in an alpine population of the self-incompatible Ranunculus acris L. (Ranunculaceae) enhances pollinator visitation and seed production. Flowers of Ranunculus acris tracked the sun during the day. Tracking accuracy was greatest during the middle of the day. The temperature elevation in flowers was negatively correlated with the flower's angle of deviation from the sun. Despite the increased temperature, insects did not discriminate among flowers on the basis of their angle of deviation from the sun, or tend to stay longer in the flowers aligned closest towards the sun. A tethering experiment was conducted on three groups of plants flowering at different times in the 1993 season and on one group the following season. Manipulation plants were constrained not to track the sun, whereas control plants tracked the sun naturally. Solar tracking had no effect on seed:ovule ratio, seed mass, or abortion rate in any of the groups. There is probably a very narrow range of weather conditions (cold, sunny, and calm) where flower heliotropism may enhance visitation rate to flowers and their seed production.     

PHOTOREACTIONS OF PARTIALLY BLINDED WHIP-TAIL SCORPIONS

The experiments dealt with in this paper were devised to ascertain (1) the relative effectiveness as photoreceptors of the whip-tail scorpion''s median eyes, lateral eye groups, and cutaneous sensitive areas, and (2) the effect on orientation produced by symmetrical and by asymmetrical interference with the photoreceptive mechanism. Each of the receptors was eliminated unilaterally and bilaterally, singly and in combinations with other receptors. In all, sixteen different abnormal conditions of the photoreceptive apparatus were produced. The reactions of animals thus partially blinded were measured in terms of angular deflection from an initial path of locomotion. Measurements obtained under anterior, lateral, and bilaterally balanced illumination were compared with measurements made on normal animals under the same conditions of illumination. The change from the normal reaction induced by covering a photoreceptor was taken as an index of the effectiveness of the receptor prevented from functioning. By comparing the values of the changes from normal reactions produced by the elimination of the several receptors, their relative effectiveness is approximated as median eyes : lateral eyes : cutaneous sensitive areas :: 1:1.6:2.2. All animals in which the receptive mechanism was rendered functionally asymmetrical exhibited, when subJected to bilaterally balanced illumination, deflections toward the side which had been made less sensitive. In a series of measurements made on animals in ten different conditions of asymmetry the amplitudes of the deflections were proportional to the degree of unbalance which had been produced in the photosensitive mechanism. Animals in which the receptive mechanism was reduced but left in a symmetrical condition maintained an undisturbed balance of reaction when subjected to equal, opposed lights. Under lateral or anterior illumination the rate of attaining a new direction of orientation was reduced in proportion to the extent of the interference with the receptive mechanism. The reactions of symmetrically and asymmetrically blinded scorpions indicate that orientation is attained and maintained by a transmission of impulses to the muscles of locomotion which is proportional bilaterally to the excitation of the symmetrically located photoreceptors. In their effect on orientation the three pairs of receptors are completely coordinated. Orientation depends upon bringing the excitation of the receptive mechanism as a whole into bilateral equilibrium.     

Compound Eye Miniaturization in Lepidoptera: a comparative morphological analysis

Superposition and apposition compound eyes are commonly associated with moths and butterflies, respectively. However, recently intermediate eye designs, combining features of both apposition and superposition eyes were found in tiny insects. Here, we examine the eyes of 12 species of moth, ranging from 1.88 to 6.03 mm body size, by scanning and transmission electron microscopy. Correlations between body and eye sizes are discussed with regard to the eyes' functionality. Although all of the species shared an ommatidial organization characteristic of pterygote insects, three optical designs were found: (a) an apposition eye, (b) an eye resembling apposition eyes, but with a unique crystalline cone, and (c) an eye intermediate in structure between apposition and superposition eyes. Our comparisons also revealed a new type of basal matrix for the Lepidoptera. The results show that in most of the examined compound eyes (with the exception of the apposition eye of Micropterix aruncella), a clear distinction between apposition and superposition eyes is not feasible. Due to functional morphological constraints as a consequence of miniaturization, evolutionary transformations from superposition into apposition optics may have occurred several times independently in various ‘microlepidopteran’ taxa. The Phyllonorycter medicaginella eye appears to illustrate this evolutionary scenario best.     

Blue light controls solar tracking by flowers of an alpine plant

In at least 18 plant families, leaves or flowers can maintain a specific orientation with respect to diurnal movements of the sun. Previous work on heliotropic leaves has demonstrated that blue light (400–500nm) provides the cue for their tracking response. Floral heliotropism occurs in several families of arctic and alpine plants, but the spectral sensitivity of the response has not been studied previously. Moreover, no studies on the spectral sensitivity of any heliotropism have been conducted on wild plants growing in their natural habitat. Working under field conditions, we used coloured acrylic filters to determine whether heliotropism by flowers of the snow buttercup (Ranunculus adoneus) is responsive to broad-band blue or red light. Flowers were able to orient towards the sun under boxes made entirely of blue-transmitting filters and in red-transmitting boxes having a single blue side that faced the sun. In these treatments, solar tracking ability was not significantly different from that observed in adjacent control flowers. In contrast, the precision of solar orientation was significantly reduced in red-transmitting boxes and red boxes with a single blue side oriented away from the sun. In the early morning, flowers covered by red-transmitting boxes failed to orient in the direction of sunrise, suggesting that this floral response, unlike that seen in some heliotropic leaves, lacks a residual‘memory’ for previous solar movements.     

Unequal saccades generated by velocity interactions in the peripheral oculomotor system

Experiments with precision eye movement recordings show binocularly unequal saccades to be present under several stimulus conditions having as a common theme ongoing low velocities at the times of the saccades. Simulations using a model of eye muscles and eyeball dynamics reproduce these unequal saccades in quantitative agreement with the experimental findings. The model uses equal innervation for the saccades, and demonstrates a peripheral interaction between the muscle forces and the eye velocities to be the cause of the large inequality of the simulated binocular saccades. Thus, the simulations provide evidence that Hering's law continues to describe the innervation patterns to corresponding muscles producing these binocularly unequal saccades found in the experimental situation.     

Flower heliotropism of <Emphasis Type="Italic">Anemone</Emphasis> <Emphasis Type="Italic">rivularis</Emphasis> (Ranunculaceae) in the Himalayas: effects on floral temperature and reproductive fitness

The flower heliotropism of Anemone rivularis (Ranunculaceae) was investigated on the Yulong Snow Mountain, near Lijiang in the northwest of the Yunnan province of China. We discovered that tepals in this species drive the peduncles to track the sun, and that this flower heliotropism was likely an adaptation for parental environmental effects on reproductive fitness. In brief, A. rivularis flowers retained sun-tracking behavior following removal of pistils and stamens, but lost heliotropic movement, if tepals were removed. Light is the major factor to affect floral heliotropism, the tepal-received light signal was in the blue frequency. Meanwhile, the peduncles were found to bend significantly on the top portion of both control flowers and those lacking pistils and stamens, but instead of keeping a vertical peduncle orientation in flowers with tepals removed. Furthermore, the floral temperature was steadier, and seed sizes and numbers were greater for control flowers than for flowers with tepals removed. Therefore, we conclude that the tepals trigger the flower heliotropism in A. rivularis and play an important role on not only increasing but also keeping optimal thermal condition of flower interior. We further conclude that flower heliotropism enhances the pollen viability and seed production, resulting in higher reproductive success for this alpine species.     

A troponin switch that regulates muscle contraction by stretch instead of calcium

The flight muscles of many insects have a form of regulation enabling them to contract at high frequencies. The muscles are activated by periodic stretches at low Ca2+ levels. The same muscles also give isometric contractions in response to higher Ca2+. We show that the two activities are controlled by different isoforms of TnC (F1 and F2) within single myofibrils. F1 binds one Ca2+ with high affinity in the C-terminal domain and F2 binds one Ca2+ in the C-terminal domain and one exchangeable Ca2+ in the N-terminal domain. We have characterised the isoforms and determined their effect on the development of stretch-activated and Ca2+-activated tension by replacing endogenous TnC in Lethocerus flight muscle fibres with recombinant isoforms. Fibres with F1 gave stretch-activated tension and minimal isometric tension; those with F2 gave Ca2+-dependent isometric tension and minimal stretch-activated tension. Regulation by a TnC responding to stretch rather than Ca2+ is unprecedented and has resulted in the ability of insect flight muscle to perform oscillatory work at low Ca2+ concentrations, a property to which a large number of flying insects owe their evolutionary success.     

THE VISUAL ACUITY OF THE HONEY BEE

1. Bees respond by a characteristic reflex to a movement in their visual field. By confining the field to a series of parallel dark and luminous bars it is possible to determine the size of bar to which the bees respond under different conditions and in this way to measure the resolving power or visual acuity of the eye. The maximum visual acuity of the bee is lower than the lowest human visual acuity. Under similar, maximal conditions the fineness of resolution of the human eye is about 100 times that of the bee. 2. The eye of the bee is a mosaic composed of hexagonal pyramids of variable apical angle. The size of this angle determines the angular separation between adjacent ommatidia and therefore sets the structural limits to the resolving power of the eye. It is found that the visual angle corresponding to the maximum visual acuity as found experimentally is identical with the structural angular separation of adjacent ommatidia in the region of maximum density of ommatidia population. When this region of maximum ommatidia population is rendered non-functional by being covered with an opaque paint, the maximum visual acuity then corresponds to the angular separation of those remaining ommatidia which now constitute the maximum density of population. 3. The angular separation of adjacent ommatidia is much smaller in the vertical (dorso-ventral) axis than in the horizontal (anterio-posterior) axis. The experimentally found visual acuity varies correspondingly. From this and other experiments as well as from the shape of the eye itself, it is shown that the bee''s eye is essentially an instrument for uni-directional visual resolution, functional along the dorso-ventral axis. The resolution of the visual pattern is therefore determined by the vertical angular separation of those ocular elements situated in the region of maximum density of ommatidia population. 4. The visual acuity of the bee varies with the illumination in much the same way that it does for the human eye. It is low at low illuminations; as the intensity of illumination increases it increases at first slowly and then rapidly; and finally at high intensities it becomes constant. The resolving power of a structure like the bee''s eye depends on the distance which separates the discrete receiving elements. The data then mean that at low illuminations the distance between receiving elements is large and that this distance decreases as the illumination increases. Since such a moving system cannot be true anatomically it must be interpreted functionally. It is therefore proposed that the threshold of the various ommatidia are not the same but that they vary as any other characteristic of a population. The visual acuity will then depend on the distance apart of those elements whose thresholds are such that they are functional at the particular illumination under investigation. Taking due consideration of the angular separation of ommatidia it is possible to derive a distribution curve for the thresholds of the ommatidia which resembles the usual probability curves, and which describes the data with complete fidelity.     

THE VISUAL INTENSITY DISCRIMINATION OF THE HONEY BEE

1. Bees respond by a characteristic reflex to a movement in their visual field. By confining the field to a series of parallel stripes of different brightness it is possible to determine at any brightness of one of the two stripe systems the brightness of the second at which the bee will first respond to a displacement of the field. Thus intensity discrimination can be determined. 2. The discriminating power of the bee''s eye varies with illumination in much the same way that it does for the human eye. The discrimination is poor at low illumination; as the intensity of illumination increases the discrimination increases and seems to reach a constant level at high illuminations. 3. The probable error of See PDF for Equation decreases with increasing I exactly in the same way as does See PDF for Equation itself. The logarithm of the probable error of ΔI is a rectilinear function of log I for all but the very lowest intensities. Such relationships show that the measurements exhibit an internal self-consistency which is beyond accident. 4. A comparison of the efficiency of the bee''s eye with that of the human eye shows that the range over which the human eye can perceive and discriminate different brightnesses is very much greater than for the bee''s eye. When the discrimination power of the human eye has reached almost a constant maximal level the bee''s discrimination is still very poor, and at an illumination where as well the discrimination power of the human eye and the bee''s eye are at their best, the intensity discrimination of the bee is twenty times worse than in the human eye.     

Unusual tension reception in an insect

Muscle tension receptors in animals monitor the tension generated by muscles. This information is important for the initiation and control of movements and for muscle tone in relation to spatial orientation and gravity. Vertebrates have tendon organs located at the musculo-tendinous junction. The number of muscle fibers attached to one receptor is in the range of 3 to 25. In insects by contrast, only a few examples are known where muscle tension is measured by only single receptors embedded in the muscle. All other muscle activity is monitored by a range of other receptors that detect strains on the cuticle or movements of the joints. Here we describe a set of approximately 200 receptor cells located on a single insect muscle. These receptor cells are associated with ovipositor muscle fibers and were preferentially responsive to muscle tension and not muscle length. Although single receptors may respond differently, their summed response to altered muscle tension characterized them as phasic-tonic type receptors. Experimental activation of muscle receptors in animals producing a basic oviposition motor pattern inhibited homonymous muscle activity without resetting the phase of the rhythm. These results suggest a potential role of tension receptors in regulating ovipositor muscle activity and in particular preventing excessive muscle tension during oviposition. The muscle receptors presented here provide the first example of tension measurement in insects by a few hundred receptor cells associated with a single muscle. Their role in motor control and relation to other tension receptors in vertebrates and invertebrates are discussed.     

Distribution of photoperiodic receptors in the compound eyes of the bean bug, Riptortus clavatus

  The bean bug, Riptortus clavatus shows a long-day photoperiodic response with respect to the control of adult diapause. The location of photoreceptors for photoperiodism was examined in this species by complete or partial removal of photoreceptor organs. Even after one compound eye or both ocelli were removed, the insects were sensitive to photoperiod. After both compound eyes were removed, however, the insects became reproductive regardless of the photoperiod. Therefore, photoreceptors for photoperiodism were not in the ocelli but in the compound eyes. To clarify whether ommatidia in compound eyes have a regional difference in reception of photoperiod, sensitivity to photoperiod was examined after one compound eye and a part of the contralateral one were removed. Only when the central region of compound eyes was removed did the insects lose sensitivity to photoperiod. It is concluded that the ommatidia in the central region of compound eyes play a principal role in the reception of photoperiod. Accepted: 23 September 1996     

江豚鼻道肌的解剖和构筑研究

江豚的鼻部肌共分为后外肌、前外肌、后内肌、前内肌和深肌5层,无间肌和大小内肌较退化,无对角膜肌。通过测定各肌的肌重、平均肌纤维长、平均肌小节长以及肌纤维角度,计算了各肌的生理横截面积,估计最大强直张力和肌鲜重对估计最大强直张力之比值等指标。鼻部肌各肌的相对肌纤维长度相似。各鼻部肌的肌纤维角度均为零。前部肌比后部肌具有较大的收缩速度和收缩位移优势,后部肌则具有较强的张力产生能力。着于额隆和唇部吻肌的张力产生能力很强。     

Extraocular muscle degeneration and regeneration after exposure of rats to incandescent radiant energy.

Exposure of albino rats to incandescent radiant energy for a short period of time in an elevated environmental temperature (39 degrees C) causes degenerative changes in the extraocular muscles. The muscle fibres regenerate and the muscles reorganize if the animals are returned to room lighting and temperature. Extraocular muscles (EOMs) were damaged first near their insertion on the eyeball. All EOMs of both eyes were affected, but the degeneration did not extend the entire length of the muscle. The peripheral fibres of each muscle were damaged before the more central fibres. Mitochondria were swollen and often contained dense bodies. Numerous vesicular profiles, possibly from the sarcotubular system, were present. Myofibrils of the more severely damaged fibres lacked typical Z-disk structures, and I-bands had disappeared by 24 h after the exposure period, a degenerative pattern which seems to be unique for this method of EOM damage. EOM degeneration appeared to be dependent on the interaction between thermal and radiant energy on the orbital contents. However, EOMs were only rarely and very slightly affected when rats were exposed to elevated temperature in the absence of incandescent radiant energy. When an opaque, black, ocular occluder was placed over one eye and the contralateral eye was left unoccluded, EOMs and retinas of occluded eyes were undamaged, while those tissues were severely damaged in unoccluded eyes. Therefore, the most critical single variable in inducing EOM degeneration appears to be exposure to radiant energy.     

Active sensing in a freely walking spider: look where to go

The Central American hunting spider Cupiennius salei, like most other spiders, has eight eyes, one pair of principal eyes and three pairs of secondary eyes. The principal eyes and one pair of the secondary eyes have almost completely overlapping visual fields, and presumably differ in function. The retinae of the principal eyes can be moved independently by two pairs of eye muscles each, whereas the secondary eyes do not have such eye muscles. The behavioural relevance of retinal movements of freely moving spiders was investigated by a novel dual-channel telemetric registration of the eye muscle activities. Walking spiders shifted the ipsilateral retina with respect to the walking direction before, during and after a turning movement. The change in the direction of vision in the ipsilateral anterior median eye was highly correlated with the walking direction, regardless of the actual light conditions. The contralateral retina remained in its resting position. This indicates that Cupiennius salei shifts it visual field in the walking direction not only during but sometimes previous to an intended turn, and therefore “peers” actively into the direction it wants to turn.     

Intravenous methylprednisolone in the treatment of Graves' ophthalmopathy.

Eleven euthyroid patients with severe Graves'' eye disease were treated with intravenous methylprednisolone and followed up for six months or more by ophthalmological assessment, orbital computed tomography (CT), photographs, and antibody measurements. Papilloedema resolved in the single patient in whom it was present; visual acuity was abnormal in seven eyes initially and in only one eye after treatment; the intraocular pressure differential, which reflects muscle dysfunction, was initially abnormal in 18 eyes but showed a progressive and distinct improvement; nine patients showed substantial improvement in inflammatory signs. Exophthalmos improved early after treatment, but this improvement was not maintained. Orbital CT showed a pronounced reduction in the bulk of eye muscles after treatment in eight of nine patients. Autoantibodies to the thyroid stimulating hormone receptor declined. Adverse effects were trivial. Thus eight patients showed a clear response to intravenous methylprednisolone as judged by ophthalmic assessment and CT scan. The two patients who showed little response and one who had none all had a long history (more than a year) of ophthalmopathy. Results were better than those with oral steroids and adverse effects less. Treatment of Graves'' eye disease is more likely to be effective if given early; patients should be referred promptly to specialist centres, where treatment with intravenous methylprednisolone should be considered.     

RAPID LEAF MOVEMENT,MICROCLIMATE, AND WATER RELATIONS OF TWO TEMPERATE LEGUMES IN THREE CONTRASTING HABITATS

Diurnal heliotropic leaf movements, microclimate, stomatal conductance and leaf water potential of two leguminous species, Strophostyles helvola and Amphicarpa bracteata, were measured in three different habitats over two growing seasons. The habitats occurred along an environmental gradient from an open, sandy beach to a closed canopy deciduous forest understory. At the beach site, heliotropism in S. helvola resulted in higher irradiances in morning and afternoon hours and lower irradiances during midday periods compared to an horizontal leaf. In an exposed forest site A. bracteata responded within minutes to penetration of the direct solar beam by orienting its leaves to steep angles. In contrast, plants in closed canopy locations showed little diurnal leaf movement. The combined results of leaf energy budget calculations and plant physiological responses suggest that ecological ramifications of these movements vary with habitat. We hypothesize that heliotropism in open habitats increases water use efficiency and maximizes carbon returns on plant investment in photosynthesis. Conversely, we hypothesize that leaf movements in understory habitats represent a morphological mechanism to avoid thermal damage, photoinhibition of the photosynthetic apparatus, and water stress associated with high irradiances.     

Muscle spindle autogenetic inhibition in the extraocular muscles of lamb

The role of extraocular muscle (EOM) proprioceptors on eye motility has been investigated in lambs on "encéphale isolé", by evaluating the tension of EOMs at various lengths and velocities of stretch before and after proprioceptive blocks. The EOM tension, in the absence of proprioceptive input, was higher than in normal conditions. Such an effect occurred at lengthening values greater than 3 mm of stretch from resting muscle length, corresponding to 18 degrees of eye deviation and was dependent on the velocity of the stretch, being more effective at high velocity. The muscle receptors responsible for this effect was determined by comparing the sensitivity to vibratory stimulation of spindles and tendon organs to the amount of inhibition provoked by the same stimulation on an EOM electromyographic activity. The tension inhibition appeared to be correlated to muscle spindle activation. Thus, the presence of muscle spindles can determine a reduction of the tension within the stretched muscles. This result suggests that the EOM length and velocity signals operate moment to moment reduction on the stiffness of the muscle which antagonizes eye displacement, thus facilitating the ocular movements.     

Control of human eye movements: II. a model for the extraocular plant mechanism

Control of eye movements is essential in accomplishing visual or perceptive tasks. The brain and central nervous system process retinal information and send nervous signals to the extraocular muscles, which exert forces that cause the eye to move. A model for the human extraocular plant, which consists of the nervous input signals, the extraocular muscles, the orbit and the globe, is proposed. The derivation is based on anatomical and physiological data as well as experiments concerned with a variety of eye movements under normal and abnormal conditions. The nervous activity controlling eye movements was estimated from electromyography and single unit studies of the extraocular nuclei. The equations describing muscle properties were discussed in a previous paper by the authors; these results were incorporated into the present model. The characteristics of the isolated globe and its visco-elastic interaction with the orbit were computed from length- tension curves and isotonic experiments. Simulations using the resulting representation accurately depicted the isotonic experiments on the isolated globe and on the total extraocular plant, the isometric forces during three different types of eye movements, and the weighted globe experiment. A future paper will show that the model accurately simulates normal eye movements of different types and amplitudes.     

Steering responses of adult and nymphal crickets to light,with special reference to the head rolling movement

Most tethered adult crickets (Gryllus bimaculatus) assumed flight postures with or without flapping their wings in a windstream. Nymphal crickets (sixth and seventh, i.e. final, instars) also displayed the flight posture in spite of the incompleteness of wing development. These adult nymphal crickets rolled their heads towards the light source in response to unequal illumination of the compound eyes only while maintaining the flight posture. The amphtude of the head rolling movements was proportional to the change of light position up to 120°C, and independent of the light intensity if the duration was longer than 1 sec. The unequal illumination could also induce a transient increase in discharge frequency of the wing muscles on both sides, a decrease in wing beat amplitude of the ipsilateral wing on the illuminated side, and bending movements of the legs and abdomen towards the light. Cutting either of the nerve connectives at any level between the subosophageal and metathoracic ganglia did not affect the response of either the head or the abdomen to illumination. These results are discussed in relation to the steering mechanism associated with the dorsal light reaction.