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  • 1
    Digitale Medien
    Digitale Medien
    Genetic population structure in two tropical sponge-dwelling shrimps that differ in dispersal potential (1993)
    Springer
    Marine biology 116 (1993), S. 459-470 
    Details
    ISSN: 1432-1793
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The spatial context in which “host races” of parasitic animals originate is a central issue in the controversial theory of sympatric speciation. Sponge-dwelling shrimps in the genus Synalpheus provide a good system for evaluating the possibility of resource-associated divergence in sympatry. I used allozyme electrophoresis to assess the genetic population structure of two Caribbean Synalpheus species sampled in 1988 to 1990 at a hierarchy of spatial scales. S. brooksi Coutière is a host-generalist, using several sponge species in an area, and develops directly, with no planktonic larval stage. G-tests and estimates of F ST revealed highly structured populations in this species, with significant differentiation among samples from individual reefs within a region, and strong divergence among regions (Panama, Belize, Florida). Moreover, samples of S. brooksi taken from the two sponges Spheciospongia vesparium (Lamarck) and Agelas clathrodes (Schmidt) in Panama, and separated by ≤3 km, showed significant differentiation at both of the loci that were polymorphic in these populations. Genetic distances between these host-associated populations averaged 〉60% greater than distances between samples from the same host species and were comparable to, or greater tha, those for some inter-regional comparisons. These genetic data corroborate a previous finding of demographic differences between the same populations. The second species, S. pectiniger Coutière, occurs only in Spheciospongia vesparium, and produces swimming larvae. Although allele frequencies in this species differed significantly among the three regions, S. pectiniger showed no differentiation within regions, and significantly lower differentiation (F ST) among regions than its direct-developing congener. These data suggest that genetic population structure in these two commensal crustaceans is related to dispersal potential, and that restricted dispersal may allow the divergence of host-associated populations on a local scale.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00350063
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  • 2
    Digitale Medien
    Digitale Medien
    Quantitative differences in mitochondrial ultrastructure of a thiobiotic and an oxybiotic turbellarian (1984)
    Springer
    Marine biology 83 (1984), S. 95-102 
    Details
    ISSN: 1432-1793
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Specimens of the thiobiotic acoel Solenofilomorpha funilis Crezée, 1975 and the oxybiotic acoel Otocelis sp. were collected from Mount Desert Island, Maine, USA in spring and summer of 1982, and the ultrastructure and distribution of their mitochondria were compared. The volume density and the surface density of the mitochondria are significantly higher in the epidermis and parenchyma of S. funilis than in the corresponding tissues of Otocelis sp. Surface densities of mitochondrial cristae are higher in all tissues studied (epidermis, muscle, and parenchyma) of S. funilis than in Otocelis sp. The differences in mitochondrial ultrastructure of these two species suggest that mitochondria in anaerobic tissues differ in function from their aerobic counterparts.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00393089
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  • 3
    Digitale Medien
    Digitale Medien
    Prey nutritional quality and the effectiveness of chemical defenses against tropical reef fishes (1992)
    Springer
    Oecologia 90 (1992), S. 333-339 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Chemical defenses ; Coral reefs ; Nutritional quality ; Plant-herbivore interactions ; Predator-prey interactions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Many coral-reef seaweeds and sessile invertebrates produce both secondary chemicals and mineral or fibrous skeletal materials that can reduce their susceptibility to consumers. Although skeletal materials often have been assumed to function as physical defenses, their deterrent effectiveness may derive from their reduction of prey nutritional quality as well as from noxiousness of the skeletal material itself. To test the relative importance of prey nutritional quality and chemical defenses in susceptibility to predation, we offered reef fishes on Guam a choice of artificial foods varying in nutritional quality (4% versus 22% protein) and in secondary chemistry (spanning approximately natural concentration ranges). Field feeding assays were performed with pachydictyol A from the pantropical brown seaweed genus Dictyota, manoalide from the Micronesian sponge Luffariella variabilis, and a brominated diphenyl ether from the Micronesian sponge Dysidea sp. The results indicated that chemical defenses were less effective in high- than in low-quality foods. In paired assays with metabolite-free controls, all three compounds at natural concentrations significantly reduced feeding by reef fishes only in assays using low-quality food, and not in assays with high-quality food. When fishes were offered an array of artificial foods varying in both food quality and metabolite concentration, food quality significantly affected fish feeding in all three cases, while secondary chemistry was significant in only one. Thus differences in nutritional quality, within the natural range among reef organisms, can be comparable to or greater in importance than secondary chemistry in affecting feeding preferences of their consumers. Reduced nutritional quality may be an important selective advantage of producing indigestible structural materials, in addition to their roles as physical support and defense, in coral reef organisms.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00317689
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  • 4
    Digitale Medien
    Digitale Medien
    Pole terms and absorption in theP-wave pion-deuteron interaction (1980)
    Springer
    The European physical journal 296 (1980), S. 35-42 
    Details
    ISSN: 1434-601X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We estimate the accuracy of the conventional ansatz of approximating the lowest order absorptiveP-wave pion-deuteron interactions by pole term amplitudes. By comparing the matrix elements of the approximate pole term and complete absorptive reaction amplitudes for elasticπd scattering we find the pole term approximation to lead to better than 10% accuracy for both theP 11 andP 33 state interactions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01415612
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  • 5
    Digitale Medien
    Digitale Medien
    Iron toxicity and other chemical soil constraints to rice in highland swamps of Burundi (1994)
    Springer
    Plant and soil 166 (1994), S. 109-115 
    Details
    ISSN: 1573-5036
    Schlagwort(e): Fe toxicity ; highland swamp ; Histosol ; Mn ; leaf mineral content ; organic carbon ; peat ; rice ; soil pH
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Iron toxicity is suspected to be a major nutritional disorder in rice cropping systems established on flooded organic soils that contain reductible iron. A pot trial was carried out to assess Fe toxicity to rice in flooded Burundi highland swamp soils with a wide range of organic carbon contents. Soil and leaf analyses were performed and total grain weight was determined. Clear Fe toxicity was diagnosed, based on leaf Fe content at panicle differentiation. Leaf Fe contents higher than 250 μg g−1 dry matter induced lower Mg (and probably Mn) uptake, and a 50% total grain weight reduction. These features were associated with exchangeable Fe equivalent fractions higher than 86%. Besides, several non-Fe toxic soils exhibited an Mg-Mn imbalance.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02185487
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