Zur ?kologie jamaikanischer Kolibriarten

Zusammenfassung Auf Jamaika brüten 4 Kolibriarten, wobei die beiden congenerischen ArtenTrochilus polytmus undTrochilus scitulus allopatrisch leben. Jede Art weist jeweils eine eindeutige Präferenz bezüglich Meereshöhe und Vegetationshöhe auf.T. polytmus undT. scitulus stimmen in diesen beiden Parametern ihrer ökologischen Nische überein. Da sich beide Arten auch gewichtsmäßig entsprechen, nehmen sie in der nektarivoren Nahrungsgemeinschaft homologe Planstellen ein.Bei den auf Jamaika untersuchten ornithophilen Blütenpflanzen wurden Zuckerkonzentrationen von 15–22% gemessen, bei einigen auch von Insekten frequentierten Pflanzenarten solche bis 44%. Der Verlauf der Nektarsekretionsrate pro Stunde in Abhängigkeit von der Tageszeit entsprach bei Pflanzen, die ausschließlich von Kolibris bestäubt wurden, dem täglichen Aktivitätsrhythmus der Kolibris. Blütenpflanzen, die sowohl von Kolibris als auch von Insekten besucht wurden, zeigten hingegen eine weitgehend konstante stündliche Nektarproduktionsrate am Tage.Artspezifisch unterschiedliche Blütenpflanzen wurden als Nahrungsquelle ausgewählt. Diese nahrungsökologische Separation ist darauf zurückzuführen, daß die Kolibriarten aufgrund ihrer Gewichtsunterschiede jeweils nur bei bestimmten ornithophilen Blütenpflanzenarten einen Nettoenergiegewinn erzielen können (z. B. Nettoenergiegewinn bei der Nahrungsaufnahme im Schwirrflug aus einer Blüte vonAsclepias currassavica vonMellisuga minima: 0.308 cal,Anthracothorax mango: — 0.661 cal).

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On the ecology of Jamaican hummingbirds

Summary On Jamaica 4 hummingbird species are resident. The congeneric speciesTrochilus polytmus andTrochilus scitulus are geographically separated (allospecies). Relative abundance depending on altitude and on height of vegetation (proportional occurence of each species in mist-netted samples s. Fig. 1,2) indicate a species-specific preference in both parameters.T. polytmus andT. scitulus correspond in both ecological parameters as well as in morphological characteristics. It is argued that both species occupy homologous niches in their range of distribution.Nectar of all studied ornithophilic plant species varied in sugar concentration from 15% to 22%. Flowering plants visited by insects and hummingbirds reached a sugar concentration in nectar of 44% (s. Tab. 1). The rate of daily nectar production per hour in plant species solely visited by hummingbirds varied according to the daily rhythm of activity of the birds (s. Fig. 3 B). Plant species visited by hummingbirds and insects showed little daily variation in nectar production per hour (s. Fig. 3 A).To gain energy benefits Jamaican hummingbirds selected flowering plants according to their weight-specific energy requirements (s. Tab. 3, 4).

     

The α-keto acids of branched-chain amino acids: Simplified derivatization for physiological samples and complete separation as quinoxalinols by packed column gas chromatography

By use of a relatively new mixed stationary phase, complete separation of the branched-chain α-keto acids as O-trimethylsilyl-quinoxalinol derivatives is achieved within 10 min by packed column gas chromatography. Precise quantification of less than 5 nmol of α-keto acids in biological samples is possible. In small aqueous samples the α-keto acids are directly derivatized without prior purification. Plasma need only be deproteinized by perchlorate and neutralized before derivatization. Average relative precision for determination of the three main branched-chain α-keto acids is ± 5.8%.     

Book Reviews

Book reviewed in this article:
Archaeology: The Distribution of Compound Fishhook Types as a Gauge of Population Interaction in the Solomon Islands. Henry Cummings
Archaeology: A Style Analysis of Pottery Sherds from Nissan Island, Papua New Guinea: An Inquiry into the Prehistory of a Stepping Stone Island and its Role in Regulating Trade and Population Interaction between the Solomons and the Bismarck Archipelago. Susan Kaplan     

Stacking of safranine in liposomes during valinomycininduced efflux of potassium ions

Liposomes were prepared from phosphatidylcholine and cardiolipin in a KCl medium and suspended in a choline chloride medium with safranine. When efflux of K⁺ was induced by valinomycin, spectral shifts characteristic of stacking were observed. Ca²⁺ inhibited the rate of stacking in a competitive manner with a K_i of about 200 μM, while La³⁺ was about 10 times more potent. When liposomes were prepared from phospholipids with a higher ratio of cardiolipin to phosphatidyl-choline the inhibition was more potent. No effect on the stacking phenomena was seen when Ca²⁺ was added after the stacking was completed. When Ca²⁺ or an organic cation with four charges, spermine, was trapped in the intraliposomal compartment, no significant change in the rate of stacking was seen. However, the extent of stacking was decreased. It is suggested that safranine is driven by a diffusion potential to a site that is inaccessible to Ca²⁺ in the medium, presumably to the inner boundaries of the liposomal membranes.     

The use of subunit exchange chromatography for the group specific fractionation of histones

Starting from the histone mixture obtained from calf thymus, the arginine rich fraction ARE⁺⁾ was coupled to organomercurial agarose via a mercaptide bond to one of its cysteines. ARE-agarose proved to be useful for a large scale affinity chromatographic separation of whole histone. In 1M NaCl, pH 4.5, highly pure histone fractions could be eluted with an urea gradient revealing increasing affinity towards ARE in the order: KAP < KAS < LAK < (ARE)_n(GRK)_n < GRK < ARE.     

The role of Ca-2+ and cyclic adenosine 3':5'-monophosphate in insulin release induced in vitro by the divalent cation ionophore A23187.

Insulin release from isolated perifused pancreatic islets was stimulated by the divalent ionophore A23187 in the absence of exogenous glucose. In addition, A23187 produced a 2-fold elevation of cyclic adenosine 3':5'-monophosphate (cAMP) levels in isolated perifused islets. The elevation of cAMP levels coincided with peak insulin release. Ionophore-induced insulin release was unaffected by pretreatment of the islets with theophylline (5 mM). Stimulation of insulin release produced by the ionophore occurred either in the presence or absence of extracellular Ca-2+; however, cAMP accumulation required the presence of extracellular Ca-2+. The ionophore (10 muM) had no effect on adenylate cyclase activity of homogenates of isolated islets. The results of this study are interpreted as indicating that intracellular Ca-2+ has an essential role in the insulin releasing mechanism, whereas the cAMP system has a modulatory effect on this process.