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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 197 (1963), S. 1183-1186 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] WILLIAMS and Williams1, following Medawar2, have suggested that natural selection should in the majority of cases prolong the reproductive lives of animals. They show, in addition, that the force of selection must fall throughout reproductive life, to reach zero when reproduction is over; for this ...
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 197 (1963), S. 1046-1047 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE visual protective adaptations of the Lepidoptera, A and the selection pressures which have given rise to them, have been the subject of intensive study in the course of the past ten years. On the whole, researches in these fields follow three main lines of attack. In the first place, it is ...
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 181 (1958), S. 1077-1078 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The experiment here reported investigates the effect of different periods of forced, tethered flight upon the strength of the rocking response, at two different intervals after eclosion. Pupal development and emergence were allowed to proceed at about 25 C. Moths stored for intervals after ...
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 178 (1956), S. 1190-1191 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Carter2 has supported the latter part of this criticism, and has proposed an alternative view. He interprets the work of Lorenz3 as showing that birds respond to only a few of the available visual characters of the objects which they perceive : The conclusion of recent studies of bird behaviour is ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 184 (1959), S. 1164-1165 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Three factors other than flight duration influence the strength of the rocking response: (1) age from eclosi n; (2) the presence of competing reproductive responses, themselves released by precurrent flight3, which may be eliminated by removal of the abdomen, either before flight, or between flight ...
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 192 (1961), S. 373-374 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Some 12 hr. before emergence was due, and just after the absorption of the moulting fluid, each surviving moth was dissected from the pupal case, and its settling behaviour examined by the techniques which have been described in ref. 2; some individuals were kept at 20 C. and tested at intervals. ...
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 401 (1999), S. 470-473 
    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
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  • 8
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The functional organisation of the central retina of the anterior median (AM) eyes of a jumping spider,Plexippus (Salticidae) is examined by anatomical, electrophysiological and optical methods. A model of the eye is derived from the data. 2. The anatomy of the AM eye is similar to that of salticid eyes described by Land (1969a) and Williams and McIntyre (1980). There are four tiers of receptors of which only the most proximal (Layer I) is a regular mosaic with rhabdoms designed to have light-guide properties. The receptor population of Layer I is homogeneous, whereas in Layers II–IV more than one receptor type can be considered to contribute to each layer. 3. Intracellular recordings from AM photoreceptors reveal only two spectral classes: green cells with peak responses at ca. 520 nm, and ultraviolet (UV) cells with peak responses at ca. 360 nm. ERGs from intact retinae exhibit similar peaks. Spectral sensitivities from pooled intracellular recordings from green cells and ERGs correspond reasonably closely. The comparison does not, therefore, support the possibility that the retina contains receptors with peak responses at longer wavelengths, although it does not exclude it. 4. Spectrally characterised cells were marked by the injection of Lucifer Yellow. From the results of 13 successful injections, (a) peripheral Layer I and peripheral and central Layer II cells are green receptors; (b) Layer IV cells are UV receptors. Central Layer I and Layer III receptors were not marked. 5. The chromatic aberration, focal length and other optical parameters of the corneal lens of the AM eye were measured directly. The lens functions essentially as a single-surface lens of refractive index 1.40, and, together with the curved interface between the anterior chamber of the eye and the receptor matrix, forms a telephoto system. 6. The spacing between receptor Layers I and IV is matched to the chromatic aberration of the eye; if green light from an object in front of the spider is focused on Layer I, UV light will be focused on Layer IV (and Layer III). 7. The distal ends of Layer I receptors form a staircase, those lying laterally being closer to Layer II than those lying medially. This staircase enables the spider to receive in-focus images from objects at distances between ca. 3 cm — ∞ in front of it. It is suggested that the scanning movements of the retinae described by Land (1969b) serve to sweep an image across the staircase so that it will be in focus on some part of Layer I, provided that the object is within that range of distances. 8. Retinal tiering (including the staircase of Layer I) compensates both for the chromatic aberration of the dioptrics of the eye and for its inability to accommodate.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-1351
    Keywords: Phototransductive membrane turnover ; Crab retinas ; Diacylglycerol lipase inhibitor ; Protein kinase C inhibitor ; Regulation of turnover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract 1. We have previously shown that the regrowth of R1-6 rhabdoms of a crab, Leptograpsus, in darkness after brief illumination is enhanced by an inhibitor of diacylglycerol lipases, U-57908 2. We now show that the effects of U-57908 are blocked by a specific inhibitor of diacylglycerol activation of protein kinase Cs, AMG-C16. However, AMG-C16 alone has no effect when results are compared to Controls in the absence of either drug. 3. After 4 h in darkness, the sizes of R1-6 rhabdoms start to increase, however retinas are treated with drugs. We presume the existence of several regulatory pathways, one of which may relate to the endogenous circadian rhythms that our previous studies have implied. 4. We have previously demonstrated that perturbation of rhabdom renewal by drugs that affect the phosphorylation/dephosphorylation of proteins might implicate factors that regulate the transcription of rhabdomeral membrane precursors. The relevant drugs provoke the differentiation of photoreceptor nuclear envelopes to endoplasmic reticulum which appears to enter the pathway for rhabdomeral renewal demonstrated by Stowe (1980). AMG-C16 blocks such nuclear envelope events. 5. Any system that demands precise regulation of physiological events if it is to function effectively can be expected to rest upon several interlocked regulatory pathways, as our cumulative results from crab retinas imply.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The anatomy and geometrical optics of the principal eyes of some neotropical jumping spiders are examined, with particular reference to the receptors of Layer I of the tiered retina. The consequence of small size and of low habitat illuminances for spatial acuity are assessed. 2. In all phylogenetically advanced salticids examined in the present study, a foveal Layer I receptor contains a single rhabdomere organised as a light-guide. The following sections discuss Layer I: 3. For open-space species, small size minimally prejudices spatial acuities: for the very largePhiale magnifica, optimal spatial acuity is estimated to be 2.3 arc min for adults, and 4.6 arc min for second-instar spiderlings. For adults of the small speciesJollas geniculatus (only slightly larger than second-instarPhiale) we obtain 5.2 arc min. 4. For species occupying habitats in the forest understory, low illuminances appear to prejudice spatial acuity. For adults of the large speciesItata completa which lives beneath broad foliage, we obtain 5.8 arc min; for the small ant-mimicFluda princeps which inhabits the litter layer, we estimate 16.8 arc min. 5. The results indicate that habitat illuminance only constrains retinal design when it is extremely low. Impaired spatial acuities in such dark habitats are predicted to limit behavioural repertoires, and, as a secondary consequence, the number of species that can co-exist in a given forest microhabitat. 6. Receptor illuminances could, in principle, be modulated by adjustments to four factors: (i) focal lengths of the corneal lenses; (ii) the extent, or absence of the pigment stops that lie directly behind them; (iii) the magnification factors afforded by the diverging components of the telephoto lens systems; (iv) the tip diameters of foveal Layer I rhabdomeres. The first parameter is not manipulated: all corneal lenses have roughly the sameF-number (≃ 1.80). Forest species usually lack a pigment stop behind the corneal lens, the power of the diverging component is reduced or virtually absent, and rhabdomere diameters are large. 7. The interface between the retinal matrix and the anterior chamber of the eye is irregularly convexiclivate in advanced salticids, two convexiclivate surfaces forming “saddles” that overlie the narrow dorsal and ventral arms of the retinal mosaics. It is confirmed that inPortia andLyssomanes, both from “primitive” subfamilies, the interfaces are not convexiclivate, as Williams and McIntyre (1980) noted.
    Type of Medium: Electronic Resource
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