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In some animals sex is determined after conception by environmental factors (environmental sex determination. ESD). In the amphipod Gammarus duebeni sex is reportedly determined by photoperiod: there is a higher proportion of males in broods reared under long-day than under short-day photoperiods. It has been proposed that this is an adaptive response to seasonal population dynamics. A test of the hypothesis would be to demonstrate changes in the degree to which sex is determined by the environment in populations from different latitudes with different dynamics. This study reports such a test. Environmental response is significantly less strong in a southern population with a long breeding season than in a northern one in which breeding is seasonally restricted. Moreover, the threshold of the ESD cue for male or female determination is not defined when the breeding season is weakly seasonal. There is a broad correlation between latitude (and hence breeding seasonality) and the strength of ESD response across a series of population studies. Similarities between the Gammarus system of sex determination and that of the Atlantic silverside Menidia menidia, a fish with thermal ESD, are discussed. 相似文献
23.
P. E. Hessler P. E. Larsen A. I. Constantinou K. H. Schram J. M. Weber 《Applied microbiology and biotechnology》1997,47(4):398-404
A search for an abundant and economical source of isoflavones, particularly genistein, led to the discovery that the erythromycin-producing
organism Saccharopolyspora erythraea also produces this promising new cancer-prevention agent. Erythromycin fermentation is a large-scale, soybean-based process
used world-wide for the commercial production of this medically important antibiotic. Results from this study indicate that
genistin (the glucoside form of genistein), which is added to the fermentation in the soybean media, was converted to genistein
through the action of a β-glucosidase produced by the organism. Genistein was co-extracted with erythromycin from the fermentation
broth, then separated from erythromycin during the second step of the purification process for the production of erythromycin.
Received 10 September 1996 / Received revision: 22 November 1996 / Accepted: 7 December 1996 相似文献
24.
Fine needle aspirates and touch imprints of 36 hyperplastic (reactive) lymph nodes were tested for the presence of keratin and desmin. Keratin-positive cells with morphologic characteristics corresponding to extrafollicular (fibroblastic) reticulum cells were found in 18% of the fine needle aspirates and 42% of the touch imprints. The number of keratin-positive reticulum cells varied from 1 to greater than 30 per slide. Desmin-positive cells with similar morphology were found in 23% of fine needle aspirates and 37% of touch imprints, and the number of such cells per slide ranged from 2 to greater than 70. The relatively frequent occurrence of keratin-positive reticulum cells in these preparations from hyperplastic lymph nodes should be taken into account if keratin antibodies are used to search for carcinoma micrometastases. 相似文献
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E Weidekamm E Bamberg D Brdiczka G Wildermuth F Macco W Lehmann R Weber 《Biochimica et biophysica acta》1977,464(2):442-447
The interaction of gramicidin A with dipalmitoyl phosphatidylcholine liposomes is investigated by Laser-Raman spectroscopy. As revealed by the methylene C-H stretching mode the phase transition of the hydrocarbon chains near 40 degree C is eliminated in the presence of gramicidin A. Liposomes prepared from a mixture of lecithin and cholesterol seem to be unaffected by gramicidin A and show only the normal broadened phase transition. 相似文献
27.
Jonathan E. Reyman 《American anthropologist》2000,102(3):635-636
The Land of Prehistory:. Critical History of American Archaeology. Alice Beck Kehoe. New York: Routledge, 1998. 288 pp. 相似文献
28.
Moran Jonathan A.; Merbach Marlis A.; Livingston Nigel J.; Clarke Charles M.; Booth Webber E. 《Annals of botany》2001,88(2):307-311
Old World pitcher plants (Nepenthes spp., Nepenthaceae) trapand digest invertebrate prey to derive nutrients, primarilynitrogen (N). In the majority of lowland Nepenthes species studiedto date, ants (Hymenoptera, Formicidae) are numerically thedominant prey taxon. Nepenthes albomarginata is unusual in showingan apparent bias towards the capture of termites (Isoptera).We tested the hypothesis that N. albomarginata derives N fromtermite capture, by comparison of foliar stable N isotope abundance( 相似文献
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