Sympatric divergence and clinal variation in multiple coloration traits of Ficedula flycatchers.

Geographic variation in phenotypes plays a key role in fundamental evolutionary processes such as local adaptation, population differentiation and speciation, but the selective forces behind it are rarely known. We found support for the hypothesis that geographic variation in plumage traits of the pied flycatcher Ficedula hypoleuca is explained by character displacement with the collared flycatcher Ficedula albicollis in the contact zone. The plumage traits of the pied flycatcher differed strongly from the more conspicuous collared flycatcher in a sympatric area but increased in conspicuousness with increasing distance to there. Phenotypic differentiation (PST ) was higher than that in neutral genetic markers (FST ), and the effect of geographic distance remained when statistically controlling for neutral genetic differentiation. This suggests that a cline created by character displacement and gene flow explains phenotypic variation across the distribution of this species. The different plumage traits of the pied flycatcher are strongly to moderately correlated, indicating that they evolve non-independently from each other. The flycatchers provide an example of plumage patterns diverging in two species that differ in several aspects of appearance. The divergence in sympatry and convergence in allopatry in these birds provide a possibility to study the evolutionary mechanisms behind the highly divergent avian plumage patterns.

Weak- and strong-coupling electrostatic interactions between asymmetrically charged planar surfaces.

We compare weak- and strong-coupling theory of counterion-mediated electrostatic interactions between two asymmetrically charged plates with extensive Monte Carlo simulations. Analytical results in both weak- and strong-coupling limits compare excellently with simulations in their respective regimes of validity. The system shows a surprisingly rich structure in terms of interactions between the surfaces as well as fundamental qualitative differences in behavior in the weak- and the strong-coupling limits.

p42 mitogen-activated protein kinase and p90 ribosomal S6 kinase are selectively phosphorylated and activated during thrombin-induced platelet activation and aggregation.

Human platelets provide an excellent model system for the study of phosphorylation events during signal transduction and cell adhesion. Platelets are terminally differentiated cells that exhibit rapid phosphorylation of many proteins upon agonist-induced activation and aggregation. We have sought to identify the kinases as well as the phosphorylated substrates that participate in thrombin-induced signal transduction and platelet aggregation. In this study, we have identified two forms of mitogen-activated protein kinase (MAPK), p42mapk and p44mapk, in platelets. The data demonstrate that p42mapk but not p44mapk becomes phosphorylated on serine, threonine, and tyrosine during platelet activation. Immune complex kinase assays, gel renaturation assays, and a direct assay for MAPK activity in platelet extracts all support the conclusion that p42mapk but not p44mapk shows increased kinase activity during platelet activation. The activation of p42mapk, independently of p44mapk, in platelets is unique since in other systems, both kinases are coactivated by a variety of stimuli. We also show that platelets express p90rsk, a ribosomal S6 kinase that has previously been characterized as a substrate for MAPK. p90rsk is phosphorylated on serine in resting platelets, and this phosphorylation is enhanced upon thrombin-induced platelet activation. Immune complex kinase assays demonstrate that the activity of p90rsk is markedly increased during platelet activation. Another ribosomal S6 protein kinase, p70S6K, is expressed by platelets but shows no change in kinase activity upon platelet activation with thrombin. Finally, we show that the increased phosphorylation and activity of both p42mapk and p90rsk does not require integrin-mediated platelet aggregation. Since platelets are nonproliferative cells, the signal transduction pathways that include p42mapk and p90rsk cannot lead to a mitogenic signal and instead may regulate cytoskeletal or secretory changes during platelet activation.

Positive fitness consequences of interspecific interaction with a potential competitor.

The coexistence of species sharing mutual resources is usually thought to be limited by negative processes such as interspecific competition. This is because an overlap in resource use leads to negative fitness consequences, and traits favouring avoidance of potential competitors, for example in habitat selection, are therefore selected for. However, species interactions are acknowledged to vary from negative (competition) to mutualism, although empirical evidence for positive interspecific interactions from natural communities of other than plants and sessile animals is scarce. Here, we experimentally examined the habitat selection and its fitness consequences of a migrant bird, the pied flycatcher (Ficedula hypoleuca), in relation to the presence of competitively superior birds, resident titmice (Parus spp.). Experiments were conducted on two spatial scales: landscape and nest-site scale. We demonstrate that pied flycatchers were attracted to and accrued fitness benefits from the presence of titmice. Flycatchers breeding in tight association with titmice initiated breeding earlier, had larger broods and heavier young than solitarily breeding flycatchers. This paradoxical result indicates that species interactions may switch from negative to positive and that the coexistence of species is not always restricted by negative costs caused by other species.

Gender differences in lipid alterations following combined pancreas-kidney transplantation.

We have previously demonstrated that the lipid profile improves following successful combined pancreas-kidney transplantation (PKT). In this study, we examined whether changes in the lipid profile were different in men than in women following PKT. Fasting total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL), and the TC to HDL ratio (TC/HDL) were evaluated in 47 patients (27 men and 20 women) with normal graft function following PKT. Lipids were evaluated at regular intervals 3.5 months to 2.2 years post-PKT (a total of 317 observations). After PKT, TC/HDL decreased (P < .05), TC was unchanged, and HDL increased (P < .05) in both men and women. Although TG decreased in both men and women, it reached statistical significance in men only (P < .05). There were no significant differences in any lipid parameters between men and women before PKT, but after PKT, TC, TG, and HDL were higher in women (240 +/- 11, 183 +/- 17, and 64 +/- 19 mg/dL, respectively) than in men (207 +/- 6, 143 +/- 11, and 53 +/- 2 mg/dL, P < .05 for each). When post-PKT values were analyzed for trends over time, both TC and TG decreased (P < .05 for both) without any significant difference in trends between men and women. When six individuals who had received lovastatin at any time during their postoperative course were removed from analysis, the gender differences in TG post-PKT and the decrease in TG over time were no longer statistically significant (P > .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Repulsion between oppositely charged macromolecules or particles.

The interaction of two oppositely charged surfaces has been investigated using Monte Carlo simulations and approximate analytical methods. When immersed in an aqueous electrolyte containing only monovalent ions, two such surfaces will generally show an attraction at large and intermediate separations. However, if the electrolyte solution contains divalent or multivalent ions, then a repulsion can appear at intermediate separations. The repulsion increases with increasing concentration of the multivalent salt as well as with the valency of the multivalent ion. The addition of a second salt with only monovalent ions magnifies the effect. The repulsion between oppositely charged surfaces is an effect of ion-ion correlations, and it increases with increasing electrostatic coupling and, for example, a lowering of the dielectric permittivity enhances the effect. An apparent charge reversal of the surface neutralized by the multivalent ion is always observed together with a repulsion at large separation, whereas at intermediate separations a repulsion can appear without charge reversal. The effect is hardly observable for a symmetric multivalent salt (e.g., 2:2 or 3:3).

Laser-induced thermal grating effects in flames.

Light scattering from a laser-induced thermal grating produced in an atmospheric-pressure H(2)/O(2) flame is observed with a phase-matching geometry commonly used in resonant four-wave mixing and laser-induced grating spectroscopy. The presence of thermal gratings is confirmed in both the time and the frequency domains in two distinct experiments. Diluting the flame with helium decreases the thermal grating signal intensity. Experimental results agree well with calculations based on a solution of the linearized hydrodynamic equations.

LETTER TO THE EDITOR

The solvation force between two planar surfaces immersed in a model liquid mimicking water is obtained using Monte Carlo computer simulations and free energy functional theory calculations. When the surfaces are hydrophilic, the solvation force is repulsive, as is the net force, provided the solvent-surface interaction is strong, compared with the surface-surface and solvent-solvent interactions. The range of the surface-solvent interaction is shown to have a profound influence on the resulting solvation force, whereas solvent orientational order is only of minor importance. We conclude that a repulsive force would also be found in a less polar solvent, confined between sufficiently solvophilic surfaces. With hydrophobic surfaces, the solvation force is attractive. The net lowering of solvent density between the surfaces increases the attraction beyond the expected van der Waals interaction. This density depression contribution is substantial even at rather large separations and will be present for all fluids confined between solvophobic surfaces. Our calculations suggest that the famous "hydrophobic force" is often dominated by density depression. Copyright 1997 Academic Press. Copyright 1997Academic Press