This study describes the activity pattern of the blue-eyed black lemur Eulemur macaco flavifrons for the first time and investigates the parameters, such as season or habitat, that may influence the distribution of activity over the 24 h cycle. Four groups of E. m. flavifrons in 2 forest fragments with different degrees of degradation were followed for 24 h mo-1 over a 7 mo period between July 2004 and July 2005. Blue-eyed black lemurs exhibited a bimodal activity pattern which peaked during the morning and evening twilight. The groups consistently showed activity bouts both during the day and at night, a behaviour that corresponds to Tattersall's (1987) definition of cathemerality. The proportion of illuminated lunar disc and the nocturnal illumination index were positively associated with the amount of nocturnal activity. Total activity, both diurnal and nocturnal, was significantly higher in the secondary than in the primary forest. In view of our results, the cathemeral behaviour of E. m. flavifrons may best be explained as flexible responses to a framework of varying environmental factors, each of which may enhance or inhibit activity within the lemurs' range of adaptability. This temporal behavioural plasticity may be an adaptation to an erratic and severe climate with frequent droughts and cyclones and unpredictable resource availability.
We investigate the influence of an additional scatterer on the tracking signal of an optically trapped particle. The three-dimensional particle position is recorded interferometrically with nanometer precision by using a quadrant photodiode in the back focal plane of a detection lens. A phase disturbance underneath the sample leads to incorrect position signals. The resulting interaction potential and forces are therefore erroneous as well. We present a procedure to correct for the disturbance by measuring its interferometric signal. We prove the applicability of our phase correction approach by generating a defined displacement of the trapped probe.
Hydrated polymer interlayers between planar lipid membranes and solid substrates provide a water reservoir and thus maintain a finite membrane-substrate distance. Linear polymer spacers attached to lipid head groups (lipopolymer tethers) can be used as a defined model of oligo- and polysaccharides covalently anchored on cell surfaces (glycocalyx). They can offer a unique advantage over membranes physisorbed on polymer films (called polymer-cushioned membranes), owing to their ability to control both the length and density of polymer chains. In this study, a lipopolymer tether composed of a stable ether lipid moiety and a hydrophilic poly(2-methyl-2-oxazoline) spacer with a length of 60 monomer units is used to fabricate supported membranes by the successive deposition of proximal (lower) and distal (upper) leaflets. Using specular X-ray reflectivity and ellipsometry, we systematically investigate how the lateral density of polymer chains influences the membrane-substrate interactions. The combination of two types of reflectivity techniques under various conditions enables the calculation of quantitative force-distance relationships. Such artificial membrane systems can be considered as a half-model of cell-cell contacts mediated via the glycocalyx, which reveals the influence of polymer chain density on the interplay of interfacial forces at biological interfaces.
We fabricated a new class of supported membranes based on monolayers of artificial bola (transmembrane) lipids. The lipids used in this study are symmetric bola lipids with two phosphocholine head groups, which resemble natural archaea lipids. To prevent bending of the hydrocarbon chains, stiff triple bonds are inserted in the middle of the hydrocarbon cores. The formation of homogeneous "monolayers" of transmembrane lipids over macroscopic areas can be monitored with fluorescence microscopy. Structures of such supported monolayers in bulk water were characterized with specular X-ray reflectivity using high energy X-ray radiation, which guarantees a high transmission through bulk water. Here, the vertical structure of single monolayers could be resolved from reconstructed electron density profiles. To verify the structural model suggested by the specular reflectivity, we also performed small-and wide-angle X-ray scattering of transmembrane lipid suspensions. The wide-angle patterns reflect a distorted chain-chain correlation, while the small-angle scattering allowed us to model an electron density profile which is consistent with the profile calculated from specular reflectivity.
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