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  • 1
    Electronic Resource
    Electronic Resource
    Butterfly optics exceed the theoretical limits of conventional apposition eyes (1987)
    Springer
    Biological cybernetics 57 (1987), S. 159-168 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Optical experiments on butterfly compound eyes show that they have angular sensitivities narrower than expected from conventional apposition eyes. This superior performance is explained by a theoretical model where the cone stalk is considered as a modecoupling device. In this model the Airy diffraction pattern of the corneal facet excites a combination of the two waveguide modes LP01 and LP02. When the two modes propagate through the cone stalk the power of LP02 is transferred to LP01 alone which is supported by the rhabdom. This mechanism produces a higher on-axis sensitivity and a narrower angular sensitivity than conventional apposition optics. Several predictions of the model were confirmed experimentally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00364148
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  • 2
    Electronic Resource
    Electronic Resource
    Built-in polarizers form part of a compass organ in spiders (1999)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 401 (1999), S. 470-473 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Some insects and vertebrates use the pattern of polarized light in the sky as an optical compass. Only a small section of clear sky needs to be visible for bees and ants to obtain a compass bearing for accurate navigation. The receptors involved in the polarization compass are confined to a ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/46773
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  • 3
    Electronic Resource
    Electronic Resource
    Circadian and light-dependent control of the pupil mechanism in tipulid flies
    Amsterdam : Elsevier
    Journal of Insect Physiology 40 (1994), S. 883-891 
    Details
    ISSN: 0022-1910
    Keywords: Circadian rhythm ; Compound eye ; Dark adaptation ; Pupil dynamics ; Pupil sensitivity ; Tipulidae ; Visual ecology
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0022-1910(94)90022-1
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  • 4
    Electronic Resource
    Electronic Resource
    The dorsal eye of the dragonfly Sympetrum: specializations for prey detection against the blue sky (1995)
    Springer
    Journal of comparative physiology 176 (1995), S. 437-453 
    Details
    ISSN: 1432-1351
    Keywords: Compound eye ; Dragonfly ; Electrophysiology ; Optics ; Photochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Dragonflies of the genus Sympetrum have compound eyes conspicuously divided into dorsal and ventral regions. Using anatomical, optical, electrophysiological, in-vivo photochemical and microspectrophotometrical methods, we have investigated the design and physiology of the dorsal part which is characterized by a pale yellow-orange screening pigment and extremely large facets. The upper part of the yellow dorsal region is a pronounced fovea with interommatidial angles approaching 0.3°, contrasting to the much larger values of 1.5°–2° in the rest of the eye. The dorsal eye part is exclusively sensitive to short wavelengths (below 520 nm). It contains predominantly blue-receptors with a sensitivity maximum at 420 nm, and a smaller amount of UV-receptors. The metarhodopsin of the blue-receptors absorbs maximally at 535 nm. The yellow screening pigment transmits longwavelength light (cut-on 580 nm), which increases the conversion rate from metarhodopsin to rhodopsin (see Fig. 11a). We demonstrate that because of the yellow pigment screen nearly all of the photopigment is in the rhodopsin state under natural conditions, thus maximizing sensitivity. Theoretical considerations show that the extremely long rhabdoms (1.1 mm) in the dorsal fovea are motivated for absorption reasons alone. A surprising consequence of the long rhabdoms is that the sensitivity gain, caused by pumping photopigment into the rhodopsin state, is small. To explain this puzzling fact we present arguments for a mechanism producing a gradient of rhodopsin concentration along the rhabdom, which would minimize saturation of transduction units, and hence improve the signal-to-noise ratio at high intensities. The latter is of special importance for the short integration time and high contrast sensitivity these animals need for spotting small prey at long distances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196410
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of energy deprivation on the fly pupil mechanism: evidence for a rigor state (1994)
    Springer
    Journal of comparative physiology 174 (1994), S. 701-706 
    Details
    ISSN: 1432-1351
    Keywords: House fly ; Compound eye ; Pupil mechanism ; Pigment migration ; Anoxia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The energy dependence of the pupil pigment-migrations in the fly Musca domestica was studied in live animals, using optical techniques and nitrogen-gas induced anoxia. The results obtained can be summarized in 3 points: 1. Energy deficiency can make the pupil mechanism stop in any state, extreme or intermediate. 2. Anoxia induced during intermittent stimulation makes the pupil stop in the closed state (aggregated pigment granules). 3. During long-term anoxia the pupil very slowly opens (dispersal of pigment granules), irrespective of ambient intensity. The slow anoxic opening (point 3) is more than 1000 times slower than that predicted for free diffusion of pigment granules in water. Assuming realistic values of cytoplasm viscosity, this implies that anoxia causes the pigment granules to attach to rigid structures in the cells, in analogy with the rigor state in anoxic muscles. The rigor phenomenon in the pupil mechanism prevents experimental discrimination between active and passive processes of pigment migration. Normal pupil opening has a time course which agrees reasonably with a passive diffusion process, but it is argued that an active transportation of granules away from the rhabdom is more likely in the dark adapted eye.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192719
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  • 6
    Electronic Resource
    Electronic Resource
    Intensity and polarization of the eyeshine in butterflies (1989)
    Springer
    Journal of comparative physiology 166 (1989), S. 51-56 
    Details
    ISSN: 1432-1351
    Keywords: Compound eye ; Optics ; Insects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The compound eyes of most diurnal butterflies have a reflecting tapetum below the retina. Light that enters the eye is guided down the rhabdom, reflected by the tapetum, and then guided back up the rhabdom. The light that is not absorbed by the rhabdom is reemitted and gives rise to an eyeshine. We have measured the fraction of the incident light that is re-emitted, and also the degree to which this light retains its original polarization. The following conclusions are drawn: 1. Even at the wavelength where the eyeshine is most intense, only a few percent of the incident photons are re-emitted. 2. The tapetum acts as a plane mirror that preserves polarization. 3. The light that passes through the rhabdom in second-order waveguide modes is depolarized to a greater extent than the light contained in first-order modes. The depolarization is expected to decrease only slightly the polarization sensitivity of the retina. 4. Theoretical modelling of the waveguide properties of the rhabdom provided a way of using depolarization measurements for estimating the refractive index of the rhabdom. The measured amount of depolarization is consistent with the dispersion of phase velocities of different second-order modes propagating in a rhabdom of refractive index 1.363.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00190209
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  • 7
    Electronic Resource
    Electronic Resource
    Relationships between pupil working range and habitat luminance in flies and butterflies (1997)
    Springer
    Journal of comparative physiology 182 (1997), S. 1-9 
    Details
    ISSN: 1432-1351
    Keywords: Key words Fly ; Butterfly ; Compound eye ; Pupil ; Visual ecology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The luminance range over which the pupil mechanism operates was measured with pupil reflectometry in 11 species of butterflies and 13 species of dipteran flies. The different species were selected to be as different as possible regarding the range of ambient luminances in which they are active. Habitat luminance ranges were also measured and correlated to luminances in the experimental situation. The pupil mechanism in butterflies operates in the centre of the luminance range in which the different species are active. Three distinct groups of butterflies with pupil sensitivities matched to their specific types of activity pattern were identified: species active only in direct sunlight, species active also in shaded places and species extending their activity into dawn and dusk. Quite differently, the pupil mechanisms of dipteran flies operate in the upper end of the ambient luminances, and in some species well above the luminances normally encountered by the animal. All fly pupils start to close roughly at the same luminance, irrespective of the luminances in which the species are active. The results suggest that the most important role for the pupil mechanism in many of the butterfly species is to maximize acuity over a wide range of luminances, whereas in flies it is to avoid saturation of transduction units and thereby maximize the photoreceptor's signal-to-noise ratio at high light intensities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003590050152
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  • 8
    Electronic Resource
    Electronic Resource
    Optics of the butterfly eye (1988)
    Springer
    Journal of comparative physiology 162 (1988), S. 341-366 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The afocal apposition optics of butterfly eyes was examined from both a geometrical optics and a wave optics point of view. We used several different species of butterfly but put special emphasis on a common Australian nymphalid,Heteronympha merope. From the anatomy of the retina, the optics of isolated components of the eye and the ophthalmoscopy of the intact living eye we derived the following. 1. The proximal part of the crystalline cone behaves as a powerful lens which, according to our measurements of optical power, turns the complete optical system into an afocal telescope with an angular magnification of 6.4 (inHeteronympha). The rhabdom tip lies in the exit pupil of the telescope and is imaged into the cornea with a magnification of 9.1 (in the same species). 2. Using light reflected from the eye's tapetum, we studied the waveguide mode phenomena of the rhabdom. Different butterflies showed either one, two or three waveguide modes, depending on the rhabdom diameter. The mode patterns were observed at four different optical planes: at the cornea, at infinity, at the back focal plane of the corneal lens — which, for this measurement, was optically neutralised — and at the plane of the deep pseudopupil. 3. During light adaptation the closure of the pupil caused the modes to disappear in sequence, starting with the highest order. The behaviour of the fading modes indicates that the pupil acts by absorption rather than by a change of refractive index around the rhabdom. 4. The modes were used to measure the waveguide parameter of the rhabdom, from which its refractive index was deduced to be 1.36. 5. The distinction between near-field and farfield versions of the mode patterns provided further evidence in favour of an afocal optical system. Two different interpretations of the butterfly optical system are discussed and we present a hypothesis to explain how both afocal apposition and refracting superposition optical systems evolved in insect eyes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00606122
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  • 9
    Electronic Resource
    Electronic Resource
    Sensitivity and dynamics of the pupil mechanism in two tenebrionid beetles (1993)
    Springer
    Journal of comparative physiology 173 (1993), S. 455-462 
    Details
    ISSN: 1432-1351
    Keywords: Pupil sensitivity ; Dark adaptation ; Compound eye ; Zophobas morio ; Tenebrio molitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Using infrared reflectometry of the deep pseudopupil, we have measured the absolute sensitivity, the dynamic range and the speed of the pupil mechanism in the acone apposition eye of two tenebrionid beetles: Zophobas morio F. and Tenebrio molitor L. The following conclusions are made from the results: 1. There is a substantial difference in sensitivity of the pupil mechanism between the two beetle species. The pupil is about 5.3 log units more sensitive in Zophobas than in Tenebrio. 2. There is also a difference in sensitivity between day and night. Surprisingly, the sensitivity is higher at day-time, and the difference is about 0.5 log units in both Zophobas and Tenebrio. 3. Light adaptation is completed faster during daytime than at night in both Zophobas and Tenebrio, whereas dark adaptation is completed about equally fast both day and night in both species. The speed of the pupil response, however, is dependent on the preceding adaptation history. 4. The pupil mechanism in both species is under the influence of a circadian rhythm, which determines the size of the pupil aperture in such a way that the pupil is maximally open when dark-adapted at night, but only partially open when dark-adapted at daytime. The differences in sensitivity and dynamics of the pupil mechanism between day and night are mainly due to the circadian rhythm setting the control range of the pupil aperture in both Zophobas and Tenebrio. The pupil differences between the two beetles are discussed regarding behavioural differences between the two species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00193518
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  • 10
    Electronic Resource
    Electronic Resource
    Did neural pooling for night vision lead to the evolution of neural superposition eyes? (1994)
    Springer
    Journal of comparative physiology 175 (1994), S. 289-302 
    Details
    ISSN: 1432-1351
    Keywords: Compound eye ; Open rhabdom ; Neural superposition ; Visual ecology ; Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Observations of the infrared deep pseudopupil, optical determinations of the corneal nodal point, and histological methods were used to relate the visual fields of individual rhabdomeres to the array of ommatidial optical axes in four insects with open rhabdoms: the tenebrionid beetle Zophobas morio, the earwig Forficula auricularia, the crane fly Tipula pruinosa, and the backswimmer Notonecta glauca. The open rhabdoms of all four species have a central pair of rhabdomeres surrounded by six peripheral rhabdomeres. At night, a distal pigment aperture is fully open and the rhabdom receives light over an angle approximately six times the interommatidial angle. Different rhabdomeres within the same ommatidium do not share the same visual axis, and the visual fields of the peripheral rhabdomeres overlap the optical axes of several near-by ommatidia. During the day, the pigment aperture is considerably smaller, and all rhabdomeres share the same visual field of about two interommatidial angles, or less, depending on the degree of light adaptation. The pigment aperture serves two functions: (1) it allows the circadian rhythm to switch between the night and day sampling patterns, and (2) it works as a light driven pupil during the day. Theoretical considerations suggest that, in the night eye, the peripheral retinula cells are involved in neural pooling in the lamina, with asymmetric pooling fields matching the visual fields of the rhabdomeres. Such a system provides high sensitivity for nocturnal vision, and the open rhabdom has the potential of feeding information into parallel spatial channels with different tradeoffs between resolution and sensitivity. Modification of this operational principle to suit a strictly diurnal life, makes the contractile pigment aperture superfluous, and decreasing angular sensitivities together with decreasing pooling fields lead to a neural superposition eye.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192988
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