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921.
Colonies of honeybees (Apis mellifera L.) were established thatvaried in the proportions of their workers that were of Europeanand hybrid (Africanized x European) descent. Colony defensiveresponses increased with higher proportions of hybrid workers.Colonies consisting exclusively of hybrid workers did not differin their response from "pure" Africanized colonies, suggestingthat the strong defensive behavior of Africanized workers isgenetically dominant. European workers became more defensivein colonies that also contained hybrid workers, whereas hybridworkers became less defensive in the same mixed colonies. Inmixed colonies hybrid workers were individually more likelythan Europeans to sting a leather target but not more likelyto guard the entrance. 相似文献
922.
Lecointre Guillaume Philippe Herv Vn Lê Hoc Lanh Le Guyader Herv 《Molecular phylogenetics and evolution》1994,3(4)
The evolution of bootstrap proportions (BP) with sequence length was studied using a 28S ribosomal RNA data set. For different sequence lengths, informative sites were jackknifed several times. Bootstrapping was subsequently performed on each of these subsamples. For each node, BPs so obtained were plotted against sequence length, showing the evolution of the robustness with increasing number of informative sites. For robust nodes (BP of 100%), the pattern of BPs is unvarying and is described by a simple function BP = 100(1− e−b(x − x′)), where x is the number of informative sites and b and x′ are two parameters estimated using a nonlinear regression procedure. When a node has a BP <100% and the pattern of BPs fits this function, it is possible to estimate the number of informative sites required to obtain a given average BP. The method also identifies nonrobust nodes (nonascending clusters of BP dots), for which it seems to be more cost effective and fruitful to turn to other species and/or genes rather than to continue sequencing longer gene lengths from the same species to reach a BP of 95%. 相似文献
923.
Intensity of bacterial flagella staining using a modified silver stain was increased by aging the mordant for one week at room temperature. The use of aged mordant increased the apparent diameters of stained flagella and resulted in a darker stain. The mordant remained stable for at least four months at room temperature. The staining protocol presented allows application to liquid or solid cultures. 相似文献
924.
William R. Gower Jr. Robert M. Risch Constantine V. Godellas Peter J. Fabri 《In vitro cellular & developmental biology. Animal》1994,30(3):151-161
Summary A new human pancreatic cancer (HPAC) cell line was established from a nude mouse xenograft (CAP) of a primary human pancreatic
ductal adenocarcinoma. In culture, HPAC cells form monolayers of morphologically heterogenous, polar epithelial cells, which
synthesize carcinoembryonic antigen, CA 19-9, CA-125, cytokeratins, antigens for DU-PAN-2, HMFG1, and AUA1, but do not express
chromogranin A or vimentin indicative of their pancreatic ductal epithelial cell character. In the presence of serum, HPAC
cell DNA synthesis was stimulated by insulin, insulin growth factor-I, epidermal growth factor, and TGF-α but inhibited
by physiologic concentrations of hydrocortisone and dexamethasone. Dose-dependent inhibition of DNA synthesis was limited
to steroids with glucocorticoid activity. The inhibitory effect of dexamethasone was abolished by the glucocorticoid antagonist
RU 38486. Binding of [3H]dexamethasone to cytosolic proteins was specific and saturable at 4° C. Scatchard analysis of binding data demonstrated
a single class of high-affinity binding sites (Kd=3.8±0.9 nM; Bmax=523±128 fmol/mg protein). Western blot analysis revealed a major protein band that migrated at a Mr of 96 kDa. Northern blot analysis identified an mRNA of approximately 7 kilobases which hybridized with a specific glucocorticoid
receptor complementary DNA probe (OB7). These findings support a role for glucocorticoids in the regulation of human malignant
pancreatic cell function. 相似文献
925.
Stephen D. Bird Robert J. Walker Michael J. Hubbard 《In vitro cellular & developmental biology. Animal》1994,30(7):420-424
Summary The effect of a conventional antibiotic (penicillin/streptomycin) mixture on the widely used kidney epithelial cell line,
LLC-PK1, was investigated by measuring growth and intracellular free calcium. Free calcium concentration was the same in cells cultured
for 3 to 7 wk with (“plus”) and without (“minus”) antibiotics both at rest and when challenged with high (14 mM) external calcium. When exposed to vasopressin, minus cells exhibited significantly smaller calcium transients than plus
cells. A similar difference existed for transients elicited by a calcium ionophore, 4-br-A23187. After longer periods of culture
(>20 wk), minus cells grew slower than plus cells but on reaching confluence (minus cells took 1 day longer) the morphologies
and viabilities were indistinguishable. The finding that culture with penicillin/streptomycin reversibly modified some properties
of LLC-PK1 cells, at least partly through altered calcium homeostasis, is of importance for workers using this cell model to study drug
effects and raises the general possibility of similar effects on other cultured cells. 相似文献
926.
Abstract. A map of burn severity resulting from the 1988 fires that occurred in Yellowstone National Park (YNP) was derived from Landsat Thematic Mapper (TM) imagery and used to assess the isolation of burned areas, the heterogeneity that resulted from fires burning under moderate and severe burning conditions, and the relationship between heterogeneity and fire size. The majority of severely burned areas were within close proximity (50 to 200 m) to unburned or lightly burned areas, suggesting that few burned sites are very far from potential sources of propagules for plant reestablishment. Fires that occurred under moderate burning conditions early during the 1988 fire season resulted in a lower proportion of crown fire than fires that occurred under severe burning conditions later in the season. Increased dominance and contagion of burn severity classes and a decrease in the edge: area ratio for later fires indicated a slightly more aggregated burn pattern compared to early fires. The proportion of burned area in different burn severity classes varied as a function of daily fire size. When daily area burned was relatively low, the proportion of burned area in each burn severity class varied widely. When daily burned area exceeded 1250 ha, the burned area contained about 50 % crown fire, 30 % severe surface burn, and 20 % light surface burn. Understanding the effect of fire on landscape heterogeneity is important because the kinds, amounts, and spatial distribution of burned and unburned areas may influence the reestablishment of plant species on burned sites. 相似文献
927.
928.
Summary For almost two decades a flock of 130 free-flying Greylag Geese (Anser anser) has been the focus of detailed ethological investigations at the Konrad Lorenz Institut in Grünau im Almtal, Austria. Gander pairs, i. e. male-male pairs, represent a prominent social unit in this flock and were the subject of a detailed behavioral investigation. Analysis of the composition and dynamics of the flock over a 15 year period indicated that the incidence of homosexual pairings closely paralleled the male bias of the sex ratio. The behavior of ganders in gander pairs was investigated and compared to that of gander and goose in heterosexual pairs. The behavior of the two males in a gander pair (1) was comparable in most aspects, (2) was similar to the behavior of the gander in heterosexual pairs, and (3) differed greatly from that of the heterosexually paired goose. Therefore, pseudo-female behavior in one partner cannot account for the formation of a pairbond between two males. As a unit, gander pairs were characterized by a higher frequency of offensive agonistic behavior compared to heterosexual pairs and spent significantly more time peripheral to, and away from the flock than did heterosexual pairs.
Zusammenfassung Das Sozialgefüge einer Schar Graugänse ist weitaus komplizierter, als es das monogame Fortpflanzungssystem erwarten ließe (Collias &Jahn 1959,Fischer 1965,Kalas 1979,Rutschke 1982). Ganterpaare, die häufig über Jahre hinweg bestehen bleiben, sind für tiersoziologische Untersuchungen interessant, weil ihre Funktion nicht im Rahmen der Fortpflanzung gesehen werden kann. Welche Bedingung begünstigen die Bildung von Ganterpaaren, und welche Verhaltensmechanismen tragen zum Entstehen und zur Aufrechterhaltung dieser Verbindung bei? Die Zusammensetzung der Grünauer Graugansschar 1973–1988 zeigt, daß die Anzahl der Ganterpaare von einem Überschuß von Männchen in der Schar abhängt. Das Verhalten von 6 Ganterpaaren wurde untersucht und mit dem von heterosexuellen Paaren verglichen. Innerhalb eines Ganterpaares entsprachen sich die Partner in der Häufigkeit von agonistischem sowie sozial-bindendem Verhalten. Homo- und heterosexuell verpaarte Ganter zeigten sich im Verhalten vergleichbar. Der Ganter eines Ganterpaares unterschied sich jedoch in der Häufigkeit aller untersuchten Verhaltensweisen von dem der heterosexuell verpaarten Gans. Folgende Schlußfolgerungen und Hypothesen bieten sich an: (1) Pseudo-weibliches Verhalten bei einem der Ganter scheint nicht die Bildung von Ganterpaaren erklären zu können. Beide Ganter verhalten sich rein männlich und behandeln den Partner so, als ob dieser ein Weibchen wäre. (2) Ein Mangel an gegengeschlechtlichen Schargenossen fördert die Bildung von homosexuellen Paaren und aufzuchtsbekannte Vögel werden dabei vorgezogen. (3) Ein Zusammenschluß mit einem gleichgeschlechtlichen Artgenossen sollte, verglichen mit der Möglichkeit alleine zu bleiben, eine überlegene Strategie darstellen, da unverpaarte Gänse geringeren Zugang zu Futterquellen haben und eher Raubtieren zum Opfer fallen. (4) Homosexuelle Paare könnten als ein Puffersystem für Ganter angesehen werden, vor allem zu Zeiten in denen das Geschlechtsverhältnis in Richtung der Männchen verschoben ist. (5) Aggression des Ganters richtet sich generell gegen andere männliche Schargenossen. Die Bildung von Ganterpaaren, also besonders aggressiven Paaren, könnte daher dazu beitragen, Ganter aus der Schar zu vertreiben und ein Übermaß von Männchen in der Schar zu verhindern. (6) Da wir zeigen konnten, daß sich homosexuelle Paare oft am Rande der Schar aufhalten und dabei häufig sichern, könnte solchen Paaren eine Art Wächterfunktion zukommen. (7) Andererseits ist es durchaus möglich, daß Ganterpaare bloß ein Epiphenomen einer Graugansschar mit einem Überschuß an Männchen darstellen.相似文献
929.
Polarized secretion of IGF-I and IGF-I binding protein activity by cultured aortic endothelial cells
W. Robert Taylor Robert M. Nerem R. Wayne Alexander 《Journal of cellular physiology》1993,154(1):139-142
Insulin-like growth factor-I (IGF-I) secretion by the vascular endothelium has been proposed to play a role in the regulation of vascular smooth muscle cell proliferation. Because vascular smooth muscle cells are adjacent to the abluminal surface of the endothelium, we tested the hypothesis that secretion of IGF-I by endothelial cells is polarized. Porcine aortic endothelial cells were cultured on permeable membranes and IGF-I measured by radioimmunoassay. Basal secretion exceeded apical secretion by a ratio of 2.3 ± 0.2:1.0 (P < 0.05). We also identified 35 kDa IGF-I binding protein activity that is preferentially secreted on the basal surface of endothelial cells. We conclude that both IGF-I and IGF-I binding protein activity secretion by endothelial cells is polarized towards the basal surface of the endothelium. A polarized secretion mechanism for IGF-I may be of importance in the normal growth and differentiation of the vasculature as well as in the development of vascular pathology. © 1993 Wiley-Liss, Inc. 相似文献
930.
Anne M. Donigan R. Christopher Cavalli Angel A. Pena C. Richard Savage Dianne Robert Soprano Kenneth J. Soprano 《Journal of cellular physiology》1993,155(1):164-170
WI-38 cells, density arrested for short periods of time, can be stimulated to re-enter the cell cycle by epidermal growth factor (EGF) alone. However, cells density arrested for longer periods have a prolonged prereplicative phase when serum stimulated and cannot be stimulated by EGF alone. Radio-ligand binding studies performed on WI-38 cells showed that actively growing cells bind [125I]EGF at relatively low levels that increase to a maximum as the cells become contact inhibited. As the cells enter a state of deeper quiescence, EGF binding falls to one-third to one-fifth the short-term growth arrested levels, remaining constant thereafter. The EGF-receptor complexes internalize more slowly in long-term growth arrested cells, and the rate of ligand association to the receptor is lower than short-term growth arrested cells. The amount of EGF receptor protein in lysates of equal numbers of both short- and long-term quiescent cells remains the same. These results suggest that the failure of long-term growth arrested cells to respond to EGF is not due to dramatic changes in the amount of receptor protein during prolonged quiescence but more likely to an alteration in the ability of these receptors to bind ligand and/or activate the EGF signal transduction pathway. © 1993 Wiley-Liss, Inc. 相似文献