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1.
JACQUES Destombes ET JEAN-LOUIS Henry 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1987,20(2):129-139
A re-examination of the trilobite Baniaspis globosa Destombes (Phacopina) from the Ashgill of the Anti-Atlas (Morocco) shows that it has several derived characters which allow us to classify it in the family Calmoniidae. Calmoniids were characteristic members of the Malvino-Kaffric province during the Lower Devonian. Hence we regard the origins of this palaeogeographic province as located on the northern Gondwanan margin as early as Ashgill, or even Caradoc, times. We agree with those authors who have suggested that the trilobite associations present in the Anti-Atlas, the Montagne Noire (France) and Bohemia during the earlier Ordovician argue against the existence of a 'proto-Tethys' ocean. 相似文献
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Fat-cells from hypothyroid rats lack the normal lipolytic response to catecholamines. We have suggested that this is due to increased sensitivity to the inhibitory actions of endogenous adenosine. In this paper we present evidence that thyroid hormones increase adipose-tissue adenosine contents and suggest that the increased sensitivity to adenosine in hypothyroidism is due to relief from desensitization by endogenous adenosine. 相似文献
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JEAN-LOUIS HENRY ET JACQUES DESTOMBES 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1991,24(3):249-253.
During the Llandeilo, the sandy lithological units which develop locally in the Armorican Massif, Spain and Morocco, are all characterized by similar trilobite associations in which endobenthic homalonotids. well adapted to shallow water and sandy substrate, are predominant. During the Llandeilo, on the northern Gondwanan margin, the wide geographical distribution of most of the trilobites, controlled by environmental factors, shows that the existence of a 'Proto-Tethys' ocean is unlikely. □ North Gondwana, Trilobita, Homalonotidae, Ordovician, Llandeilo. palaeoenvironment. 相似文献
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Out of Africa and back again: nested cladistic analysis of human Y chromosome variation 总被引:18,自引:3,他引:15
Hammer MF; Karafet T; Rasanayagam A; Wood ET; Altheide TK; Jenkins T; Griffiths RC; Templeton AR; Zegura SL 《Molecular biology and evolution》1998,15(4):427-441
We surveyed nine diallelic polymorphic sites on the Y chromosomes of 1,544
individuals from Africa, Asia, Europe, Oceania, and the New World.
Phylogenetic analyses of these nine sites resulted in a tree for 10
distinct Y haplotypes with a coalescence time of approximately 150,000
years. The 10 haplotypes were unevenly distributed among human populations:
5 were restricted to a particular continent, 2 were shared between Africa
and Europe, 1 was present only in the Old World, and 2 were found in all
geographic regions surveyed. The ancestral haplotype was limited to African
populations. Random permutation procedures revealed statistically
significant patterns of geographical structuring of this paternal genetic
variation. The results of a nested cladistic analysis indicated that these
geographical associations arose through a combination of processes,
including restricted, recurrent gene flow (isolation by distance) and range
expansions. We inferred that one of the oldest events in the nested
cladistic analysis was a range expansion out of Africa which resulted in
the complete replacement of Y chromosomes throughout the Old World, a
finding consistent with many versions of the Out of Africa Replacement
Model. A second and more recent range expansion brought Asian Y chromosomes
back to Africa without replacing the indigenous African male gene pool.
Thus, the previously observed high levels of Y chromosomal genetic
diversity in Africa may be due in part to bidirectional population
movements. Finally, a comparison of our results with those from nested
cladistic analyses of human mtDNA and beta-globin data revealed different
patterns of inferences for males and females concerning the relative roles
of population history (range expansions) and population structure
(recurrent gene flow), thereby adding a new sex-specific component to
models of human evolution.
相似文献
6.
Herwig Bachmann Douwe Molenaar Michiel Kleerebezem Johan ET van Hylckama Vlieg 《The ISME journal》2011,5(5):929-932
Cooperative behavior is widely spread in microbial populations. An example is the expression of an extracellular protease by the lactic acid bacterium Lactococcus lactis, which degrades milk proteins into free utilizable peptides that are essential to allow growth to high cell densities in milk. Cheating, protease-negative strains can invade the population and drive the protease-positive strain to extinction. By using multiple experimental approaches, as well as modeling population dynamics, we demonstrate that the persistence of the proteolytic trait is determined by the fraction of the generated peptides that can be captured by the cell before diffusing away from it. The mechanism described is likely to be relevant for the evolutionary stability of many extracellular substrate-degrading enzymes. 相似文献
7.
Kite GC Stoneham CA Veitch NC Stein BK Whitwell KE 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2006,838(1):63-70
Liquid chromatography-mass spectrometry (LC-MS) analysis of methanol extracts of Oenanthe crocata roots revealed that oenanthotoxin co-eluted with another major polyalkyne, 2,3-dihydro-oenanthotoxin, using the existing high performance liquid chromatography (HPLC) method (isocratic elution from C18 with aqueous methanol) for investigating Oenanthe poisoning. Positive ES or APCI gave [(M+H)-H(2)O](+) and its methanol adduct as major ion species for oenanthotoxin, whereas 2,3-dihydro-oenanthotoxin formed [M+H](+) and its methanol adduct. The two polyalkynes could be chromatographically resolved on C18 by gradient elution with aqueous acetonitrile. This provides superior analysis for oenanthotoxin using HPLC with photodiode array (PDA) detection alone, but for LC-MS/MS aqueous acetonitrile was less suitable due to poor ionisation and, with APCI, an increase in the relative abundance of a [M-1](+) species, which could confuse compound assignment. HPLC-PDA and LC-MS/MS methods using an aqueous acetonitrile or aqueous methanol mobile phase, respectively, were successful when applied to the analysis of the stomach contents of a pony suspected to have eaten O. crocata. Relevant product ion spectra, by ion trap MS/MS, accurate mass data and complete sets of (1)H and (13)C NMR spectral assignments are given for the two compounds. 相似文献
8.
F. J. Russell Stoneham 《BMJ (Clinical research ed.)》1952,2(4783):565-566
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Waka Yokoyama Hitoshi Kohsaka Kayoko Kaneko Matthew Walters Aiko Takayasu Shin Fukuda Chie Miyabe Yoshishige Miyabe Paul E Love Nobuhiro Nakamoto Takanori Kanai Kaori Watanabe-Imai Trevor T Charvat Mark ET Penfold Juan Jaen Thomas J Schall Masayoshi Harigai Nobuyuki Miyasaka Toshihiro Nanki 《Arthritis research & therapy》2014,16(5)