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  • 1
    ISSN: 1432-0762
    Keywords: Keywords Sex allocation ; Differential mortality ; Rearing conditions ; Brood sex composition ; Lesser black-backed gull ; Larus fuscus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Empirical evidence is growing that the offspring sex ratio in birds can be biased in relation to the body condition of parents during breeding. The sex ratio bias may come about because (1) the actual production of the two sexes may be skewed and/or (2) there may be a sex bias in early nestling mortality contingent on parental condition. By manipulating parental condition and giving them a control brood to rear, thereby eliminating effects operating via the eggs, we examined the extent to which parental condition influences the post-hatching survival of male and female lesser black-backed gulls, Larus fuscus. We found that the pre-fledging survival of male chicks was strongly reduced in all-male broods reared by parents in poor condition. Pre-fledging survival of female chicks was, however, unaffected by parental condition or brood sex composition. Thus, independently of any production biases, sex differences in nestling mortality alone can bias the offspring sex ratio at fledging in relation to the prevailing rearing conditions. In other studies on gulls we have, however, also shown that females in poor condition at laying preferentially produce female eggs. Clearly a bias in fledging sex ratio can occur within the same species due to a combination of differential production and differential post-laying mortality; the latter can involve a differential effect of poor egg quality on male and female offspring, differential effects of brood sex composition on their survival and a difference in the capacity of parents to rear males and females. All of these processes need to be taken into account in attempting to understand offspring sex ratios.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0878
    Keywords: Retina ; Xenopus ; Rods ; Cones ; Hemicholinium-3 ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Hemicholinium-3 (HC-3), a drug which prevents synthesis of acetylcholine in neurons, when injected intraperitoneally in doses as low as 2×5 mg/kg produces marked ultrastructural changes and damage in rod but not in cone photoreceptors. In rods it causes a reduction in cytoplasmic back-ground density, swelling of the endoplasmic reticulum, ballooning of the outer membrane of the nucleus, leaching of the nucleoplasm and clumping of the nuclear chromatin. In dark-adapted rods HC-3 produces some loss of cytoplasmic synaptic vesicles but no reduction in numbers of those vesicles which lie adjacent to the synaptic ribbons. In light-adapted rods the drug does not cause such an apparent reduction of synaptic vesicles but does induce a considerable reduction in numbers of vesicles associated with the ribbons. These structural changes are discussed in the light of what is known about the pharmacology of HC-3 and neurotransmitter release from vertebrate photoreceptors.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-9583
    Keywords: cognitive styles ; diagrammatic reasoning ; logic teaching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Linguistics and Literary Studies , Computer Science
    Notes: Abstract Computer-based logic proofs are a form of “unnatural” language in which the process and structure of proof generation can be observed in considerable detail. We have been studying how students respond to multimodal logic teaching, and performance measures have already indicated that students' pre-existing cognitive styles have a significant impact on teaching outcome. Furthermore, a large corpus of proofs has been gathered via automatic logging of proof development. This paper applies a series of techniques, including corpus statistical methods, to the proof logs. The results indicate that students' cognitive styles influence the structure of their logical discourse, via their differing methods of handling abstract information in diagrams, and transferring information between modalities.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-9710
    Keywords: seabirds ; sandeels ; industrial fisheries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sandeels, especiallyAmmodytes marinus are a major component of the diet of many predatory fish, seabirds and seals. The industrial fishery for sandeels is now the largest of the North Sea fisheries. A sandeel fishery in the Shetland area began in 1974 but has recently declined. This change was accompanied by dramatic declines in the breeding success of certain seabirds, particularly Arctic terns and kittiwakes. Current information on seabirds and sandeels in the Shetland area is reviewed and areas where further research is needed, highlighted. The Shetland problem illustrates the difficulties of reconciling conservation and exploitation when fundamental ecological and behavioural knowledge is lacking, and also the need to obtain further information on the ecological impact of industrial fisheries.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0878
    Keywords: Lateral-line ; Xenopus laevis ; Sensory cell ; Synaptic bar ; Neurotransmitters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Lateral-line sensory cells of Xenopus show considerable similarity to central nervous system synapses in their responses to the zinc iodide-osmium tetroxide, and bismuth-iodide cytochemical staining techniques. Both reserpine and FLA-63 cause a reduction in the diameter and electron density of the synaptic bars, and a dramatic loss of synaptic vesicles surrounding the bars. Aminooxy acetic acid and 3-mercaptopropionic acid cause no significant changes in the sensory-cell afferent synaptic apparatus. The results are discussed in the light of the known effects of the drugs. It is concluded that a monoamine rather than an amino acid may act as the afferent transmitter.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-0878
    Keywords: Retina ; Xenopus laevis ; Photoreceptors ; Synaptic ribbons ; Dense-core vesicles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Photoreceptor synapses in Xenopus retina were studied after exposure to day/night cycles and continuous light or dark. In the rods, dense-core vesicles appear alongside the synaptic ribbons in animals exposed to light. In dark-adapted rods, electron-dense material is present in the synaptic clefts, but no dense-core vesicles are found associated with the synaptic ribbons. Cone photoreceptors do not show these ultrastructural changes in response to light and dark. Prolonged exposure to light (21 days) causes flattening of the synaptic vesicles associated with the synaptic ribbons in both rods and cones. The results are discussed in the light of what is known about transmitter release from photoreceptors.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1040-452X
    Keywords: Cattle ; IVM ; IVC ; IVF ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The aim of the present series of experiments was to investigate the effect of the size of follicle from which the oocytes originate on their subsequent in vitro developmental ability. Ovarian follicles were isolated and grouped according to size (2-6 mm, 〉6 mm). Primary oocytes were carefully liberated and grouped according to morphology into one of five categories: denuded; expanded; with two or three layers of cumulus; with four or five layers; and with many (six or more) layers. Following in vitro maturation (IVM), fertilization (IVF), and culture (IVC), more oocytes with many layers of cumulus (P 〈 0.01, 70.2%, 73/104 vs. 46.8%, 87/186, respectively) and a higher proportion of blastocysts were obtained from follicles 〉 6 mm compared to 2-6 mm follicles (P 〈 0.01, 65.9%, 60/91 from 〉6 mm follicles vs. 34.3%, 34/99 from 2-6 mm follicles, respectively). Use of follicular fluid (BFF) from follicles of different sizes in the IVM medium did not significantly increase the cleavage rate or blastocyst yield compared to controls. Administration of procine folliclestimulating hormone (pFSH) to donors prior to slaughter was investigated as a possible means of increasing the number of larger sized follicles in the ovaries and, thereby, the quality of the recovered oocytes. It was found that administration of six injections of pFSH beginning 3 days prior to slaughter resulted in a significant increase (P 〈 0.001) in the proportion of follicles 〉6 mm in diameter (31.6%) compared to that in nontreated controls (6.6%) and to animals that received only four injection groups (9.4%). The blastocyst yield from oocytes originating from 〉6 mm follicles, whether from unstimulated or from pFSH-treated animals, was approximately double that of oocytes from 2-6 mm follicles (P 〈 0.01; 42.9%, 24/56 for 〉6 mm follicles vs. 22.8%, 21/92 for 2-6 mm follicles, respectively, for the 6 pFSH group; P 〉 0.05; 62.5%, 5/8 for 〉6 mm follicles vs. 32.8%, 22/67 for 2-6 mm follicles, respectively, for the control). © 1994 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Animal Behaviour 31 (1983), S. 1237-1243 
    ISSN: 0003-3472
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Animal Behaviour 28 (1980), S. 521-527 
    ISSN: 0003-3472
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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