Effects of fire on landscape heterogeneity in Yellowstone National Park,Wyoming

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.     

Male-male pairs in Greylag Geese (Anser anser)

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.

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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.

     

Polarized secretion of IGF-I and IGF-I binding protein activity by cultured aortic endothelial cells

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.     

Epidermal growth factor receptors lose ligand binding ability as WI-38 cells progress from short-term to long-term quiescence

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.     

ATP-induced Secretion in PC12 Cells and Photoaffinity Labeling of Receptors

Abstract— Secretion of catecholamines by rat PC12 cells is strongly stimulated by extracellular ATP via a P₂-type pur-inergic receptor. ATP-induced norepinephrine release was inhibited 80% when extracellular Ca²⁺ was absent. Only four nucleotides, ATP, ATPγS, benzoylbenzoyl ATP (BzATP), and 2-methylthio-ATP, gave substantial stimulation of norepinephrine release from PC12 cells. ATP-induced secretion was inhibited by Mg²⁺, and this inhibition was overcome by the addition of excess ATP suggesting that ATP^4-was the active ligand. ATP-induced secretion of catecholamine release was enhanced by treatment of cells with pertussis toxin or 12- O -tetradecanoylphorbol 13-acetate. The stimulatory effects of 12- O -tetradecanoyl-phorbol 13-acetate and pertussis toxin on norepinephrine release were additive. After brief exposure of intact cells to the photoaffinity analog, [α-³²P]BzATP, two major proteins of 44 and 50 kDa and a minor protein of 97 kDa were labeled. An excess of ATP-γS and BzATP but not GTP blocked labeling of the proteins by [³²P]BzATP. Labeling of the 50-kDa protein was more sensitive to competition by 2-methylthio-ATP than the other labeled proteins, suggesting that the 50-kDa protein represents the P₂ receptor responsible for ATP-stimulated secretion in these cells.     

Basis for Phospholipid Incorporation into Peripheral Nerve Myelin

Abstract: To characterize the mechanism(s) for targeting of phospholipids to peripheral nerve myelin, we examined the kinetics of incorporation of tritiated choline-, glycerol-, and ethanolamine-labeled phospholipids into four subfractions: microsomes, mitochondria, myelin-like material, and purified myelin at 1, 6, and 24 h after precursors were injected into sciatic nerves of 23–24-day-old rats. As validation of the fractionation scheme, a lag (> 1 h) in the accumulation of labeled phospholipids in the myelin-containing subfractions was found. This lag signifies the time between synthesis on organelles in Schwann cell cytoplasm and transport to myelin. In the present study, we find that sphingomyelin (choline-labeled) accumulated in myelin-rich subfractions only at 6 and 24 h, whereas phosphatidylserine (glycerol-labeled) and plasmalogen (ethanolamine-labeled) accumulated in the myelin-rich fractions by 1 h. The later phospholipids accumulate preferentially in the myelin-like fraction. These results are consistent with the notion that the targeting of sphingomyelin, a lipid present in the outer myelin leaflet, is different from the targeting of phosphatidylserine and ethanolamine plasmalogen, lipids in the inner leaflet. These findings are discussed in light of the possibility that sphingomyelin targeting is Golgi apparatus based, whereas phosphatidylserine and ethanolamine plasmalogen use a more direct transport system. Furthermore, the routes of phospholipid targeting mimic routes taken by myelin proteins P₀ (Golgi) and myelin basic proteins (more direct).