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41.
MICHAEL A. GIBSON THOMAS W. BROADHEAD 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1989,22(3):287-299
Gibson, Michael A. & Broadhead, Thomas W. 1989 07 15: Species-specific growth responses of favositid corals to soft-bottom substrates. Lethaia , Vol. 22, pp. 287–299. Oslo. ISSN 0024–1164.
Species of favositid corals from the Upper Silurian and Lower Devonian of Tennessee, USA, exhibit structural modifications related to corallum geometry, interfacial skeletal material, and biotic associations that enabled them to survive in terrigenous mud rich environments. Favosites conicus Hall (Lower Devonian) had a flat, holotheca-covered base and a radial pattern of colony growth, but apparently had a short life span and may not have survived beyond the first reproductive cycle (monocarpous). It was adapted for living between major episodes of terrigenous mud influx. F. foerstei (Lower Devonian) had a convex, pseudoholotheca-covered base and a modified axial pattern of colony growth. Its large size, in comparison to that of F. conicus , suggests a longer lived colony (polycarpous), in which continued upward and outward growth enabled it to survive episodic sediment influx. F. forbesi (Upper Silurian) exhibited radial growth to form either (1) a globose corallum that was symbiotic with the stalks of living crinoids permitting the colony to live entirely above the substrate, or (2) a Gorallum with a steeply convex, holotheca-covered base that represents a bottom-dwelling colony in which the rate of growth probably only slightly exceeded the rate of sediment accumulation. * Functional morphology, astogeny, paleoecology, Tabulata . 相似文献
Species of favositid corals from the Upper Silurian and Lower Devonian of Tennessee, USA, exhibit structural modifications related to corallum geometry, interfacial skeletal material, and biotic associations that enabled them to survive in terrigenous mud rich environments. Favosites conicus Hall (Lower Devonian) had a flat, holotheca-covered base and a radial pattern of colony growth, but apparently had a short life span and may not have survived beyond the first reproductive cycle (monocarpous). It was adapted for living between major episodes of terrigenous mud influx. F. foerstei (Lower Devonian) had a convex, pseudoholotheca-covered base and a modified axial pattern of colony growth. Its large size, in comparison to that of F. conicus , suggests a longer lived colony (polycarpous), in which continued upward and outward growth enabled it to survive episodic sediment influx. F. forbesi (Upper Silurian) exhibited radial growth to form either (1) a globose corallum that was symbiotic with the stalks of living crinoids permitting the colony to live entirely above the substrate, or (2) a Gorallum with a steeply convex, holotheca-covered base that represents a bottom-dwelling colony in which the rate of growth probably only slightly exceeded the rate of sediment accumulation. * Functional morphology, astogeny, paleoecology, Tabulata . 相似文献
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44.
THOMAS N. SHERRATT ANGUS D. MACDOUGALL 《Biological journal of the Linnean Society. Linnean Society of London》1995,55(2):93-107
A number of foraging studies have demonstrated that populations of predators rarely consist of individuals with identical preferences for particular types of prey. Variation among predators can lead to frequency-dependent changes in population preference, because those predators mat prefer the rarer type of prey generally have the greatest influence on population preference. In this study we develop a series of theoretical models which demonstrate how anti-apostatic selection (i.e. selection against the rare form) can arise out of (a) bimodal and (b) normal variation in preference among individuals of the same species. We show that population level anti-apostatic selection can occur even when individual predators show pro-apostatic selection (i.e. selection against the common form). Furthermore, patterns of population prey selection that arise out of variation in preference can potentially be pro-apostatic over one range of relative densities and anti-apostatic over another range of relative densities. Finally, we examine a case study involving predation by female waterboatmen Notonecta glauca and show that the variation in preference in this species is large enough to generate higher anti-apostatic selection than would be expected from the diet selected by the average individual. 相似文献
45.
Isozymes and DNA markers in gene conservation of forest trees 总被引:6,自引:0,他引:6
THOMAS GEBUREK 《Biodiversity and Conservation》1997,6(12):1639-1654
For long-lived plants that have to cope with high temporal and spatial environmental heterogeneity, genetic diversity is of
prime importance for species persistence. Detrimental anthropogenic impact on the gene pool of forest trees calls for conservation
of genetic resources. Potentials and limitations of isozymes and DNA markers in forest genetic conservation are reviewed.
These markers can contribute to conservation with respect to the delimitations of species and hybrid zones, as well as the
assessment of genetic diversity within and among populations. Markers are valuable to identify resource populations, since
today‘s genetic diversity in forest trees is predominantly the result of plant history (e.g. glacial refuges, migration).
Several suggestions have been put forward to optimize sampling of in situ or ex situ populations on the grounds of marker
data. Restraint in this area is recommended. Different types of genetic markers (terpenes, isozymes, nuclear and extrachromosomal
DNA polymorphisms) and quantitative traits yield different information about genetic diversity and population differentiation.
Hence identification of resource populations should not solely be based upon a certain marker type or on quantitative traits
alone. The capability of available markers to predict or assess adaptive potentials in forest tree populations is still very
limited.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
46.
THOMAS O. C. NDUBIZU 《The Annals of applied biology》1977,86(2):153-161
Verticillium dahliae but not V. albo-atrum Berth was isolated from eight out of twenty-one stone fruit orchards surveyed for Verticillium wilt disease in western New York. Wilt incidence was related to the cultivation of tomato or legumes as previous or inter-crop with stone fruit trees. A limited cross species inoculation using isolates of V. albo-atrum and V. dahliae from woody and herbaceous plants showed that peach and cherry were susceptible to both species. The effect of V. dahliae on growth of cherry seedlings in the presence of Tylenchorynchus claytoni, Pratylenchus penetrans and Meloidogyne hapla was compared. P. penetrans and M. hapla produced more severe growth reduction than T. claytoni. The adverse effect of Verticillium on the growth of cherry seedlings was greater acting together with any one of the three nematodes than acting alone. V. dahliae was shown to be capable of passage through earthworms without loss of infectivity. 相似文献
47.
Tomato fruits of six cultivars were harvested at three different stages of maturity or were harvested when mature-green and then stored in a modified gas atmosphere (2·5-4% O2; 4% CO2) for 2 months. The fresh and stored fruits were analysed for their contents of sugars, organic acids and free amino acids, while proteins were separated by discontinuous electrophoresis on polyacrylamide gels. In general, the low molecular weight components decreased during storage. A comparison of mature-green fruits before and after storage showed that although total protein was not decreased, a different electrophoretic pattern was obtained following controlled atmosphere (CA) storage. Thus, although controlled atmosphere storage repressed the loss of chlorophyll and synthesis of lycopene, carotenoids and xanthophylls, the biochemical parameters measured showed a controlled change towards the conditions exemplified by ripe fruits. This was not so marked in some cultivars as it was in others. 相似文献
48.
Dark Respiration of Several Varieties of Winter Wheat Given Different Amounts of Nitrogen Fertilizer 总被引:1,自引:1,他引:0
Carbon dioxide production in the dark by ears and by the restof the shoot of winter wheat grown in the field was measuredin 2 years during grain growth. The respiration rate per g d.wt of the ears was increased by nitrogen fertilizer. Ears ofthe semi-dwarf varieties Maris Fundin and Hobbit respired moreslowly than ears of Maris Huntsman and Cappelle-Desprez. Respirationrates of the rest of the shoot were unaffected by nitrogen orvariety. The amount of carbohydrate required to provide the CO2 respiredduring the whole period of grain growth varied from 163 to 443g m2, or 42 to 76 per cent of the dry weight of the grain.More than half the CO2 lost was respired by the ear. The additionof 180 kg N ha1, which increased grain yield by 78 percent in 1975, almost trebled the amount of CO2 lost by the ears.The semi-dwarf varieties lost less CO2 from ears and shootsthan did the taller ones, and had larger yields of grain. Respiration was also estimated from the difference between the14C contents of shoots sampled immediately after a 30 s exposureto 14CO2 and at maturity. When 14C was supplied 10 days afteranthesis, the loss by maturity amounted to 1628 per centof that initially absorbed by flag leaves and 40 per cent ofthat absorbed by the leaf below the flag leaf. Most of the lossoccurred in the first day. The loss of 14C by maturity was significantlyincreased by nitrogen fertilizer in 1975. Triticum aestivum L., wheat, respiration, nitrogen supply, fertilizer treatment 相似文献
49.
THOMAS SUSAN M.; HALL NIGEL P.; MERRETT MICHAEL J. 《Journal of experimental botany》1978,29(5):1161-1168
Photosynthesis, photorespiration, and ribulose bisphosphatecarboxylase/oxygenase activities were measured in intact flagleaves of wheat during ageing. Photorespiration declined verylittle as the leaves aged, and much less than photosynthesis.These changes could not be explained by changes in the ribulosebisphosphate carboxylase to oxygenase ratio of fraction 1 protein.As the leaves grew older the enzyme activities in extracts ofleaves declined in parallel so the ratio remained constant. 相似文献
50.
Isoperoxidases in Epidermal Layers of Tobacco and Changes during Organ Formation in vitro 总被引:1,自引:0,他引:1
The content and pattern of soluble isoperoxidases were determined in epidermal explants taken from different internodes of tobacco plants in the vegetative and floral states. There were qualitative and quantitative differences in the isoperoxidases, with a decrease in content and fewer bands being observed acropetally, i.e., in going from the base of the stem towards the apex. Epidermal explants from floral branches were grown in in vitro culture, with various media moditications, to form de novo floral or vegetative buds, roots or callus. Changes in soluble isoperoxidases were followed electrophoretically in relation to these varying morphogenetic pathways. In each of them, the number of bands increased on both the anodic and cathodic sides with time in culture. Compared to each other these four morphogenetic programmes were different in their peroxidase zymograms, mainly through varying kinetics in the development of activity of the isoenzymes. The changes observed during root and vegetative bud formation agree with previously published data, and the changes during floral bud formation agree with those observed in vivo. 相似文献