Within-clutch patterns of yolk testosterone vary with the onset of incubation in black-headed gulls

Hatching asynchrony in birds produces an age and size hierarchyamong siblings. Later-hatching chicks have a competitive disadvantage,and brood reduction may occur when food availability is insufficientto raise all chicks. When early-hatched chicks fail to surviveor if the circumstances allow raising all chicks, mothers shouldreverse the disadvantage to later-hatched chicks. Increasingdeposition of maternal androgens with the laying sequence hasbeen suggested to compensate for detrimental effects of hatchingasynchrony, allowing a more precise adjustment of the survivalprobabilities of each chick. Here, we show for black-headedgulls that the increase in yolk testosterone with each successiveegg is greater when the mother incubates longer before clutchcompletion, which is the major determinant of the degree ofhatching asynchrony. This finding supports the idea that yolktestosterone has a compensatory function in the context of hatchingasynchrony. Our data further show that if the time needed tocomplete a clutch is lengthened, the developmental differencesdue to incubation between the first- and the last-laid eggsincrease. In addition, the onset of incubation before clutchcompletion occurs sooner as the breeding season progresses.Both long inter-egg intervals and the seasonal shift in incubationbehavior enhance the necessity of compensation for later-hatchingchicks. Indeed, yolk levels of testosterone increased more steeplyover the laying order, if the duration of the egg-laying periodwas extended and in later-laid clutches. We suggest that prolactinplays a key role in the adjustment of testosterone allocationto the incubation pattern.     

Incorporation of isosorbide into poly(butylene terephthalate) via solid-state polymerization

The biomass-based monomer isosorbide was incorporated into poly(butylene terephthalate) (PBT) by solid-state polymerization (SSP) using the macrodiol monomer BTITB-(OH) 2, which consists of isosorbide (I), terephthalic acid (T), and 1,4-butandiol (B) residues. This macromonomer can be synthesized by a simple one-pot, two-step reaction. Polymers with number-average molecular weights up to 100,000 g x mol (-1) were readily synthesized from various ratios of PBT/BTITB-(OH) 2. Their molecular weights, thermal properties, and colors were compared with corresponding copolyesters that were obtained by melt polycondensation. We found that T m, T c, and especially T g were superior for materials that were obtained by SSP. This is ascribed to differences in the microstructures of both types of copolyesters; the SSP products exhibit a more blocky structure than do the more random melt-polymerized counterparts. The SSP method resulted in much higher molecular weights and much less colored polymers, and it seems to be the preferred route for incorporating biobased monomers that exhibit limited thermal stability into engineering plastics.     

Signaling across myoendothelial gap junctions--fact or fiction?

Gap junctions interconnect vascular cells homocellularly, thereby allowing the spread of signals along the vessel wall, which serve to coordinate vessel behavior. In addition, gap junctions provide heterocellular coupling between endothelial and vascular smooth muscle cells, creating so-called myoendothelial gap junctions (MEGJs). Endothelial cells control vascular tone by the release of factors that relax vascular smooth muscle. Endothelial factors include nitric oxide, prostaglandins, and an additional dilator principle, which acts by smooth muscle hyperpolarization and is therefore named endothelium-derived hyperpolarizing factor (EDHF). Whether this principle indeed relies on a factor or on intact MEGJs, which allow direct current transfer from endothelial to smooth muscle cells, has recently been questioned. Careful studies revealed the presence of vascular cell projections that make contact through the internal elastic lamina, exhibit the typical GJ morphology, and express connexins in many vessels. The functional study of the physiological role of MEGJs is confined by the difficulty of selectively blocking these channels. However, in different vessels studied in vitro, the dilation related to EDHF was sensitive to experimental interventions that block MEGJs more or less specifically. Additionally, bidirectional electrical coupling between endothelial and smooth muscle cells was demonstrated in isolated small vessels. In marked contrast, similar approaches used in conjunction with intravital microscopy, which allows examination of vascular behavior in the intact animal, did not verify electrical or dye-coupling in different models investigated. The discrepancy between in vitro and in vivo investigations may be due to size and origin of the vessels studied using these distinct experimental approaches. Additionally, MEGJ coupling is possibly tightly controlled in vivo by yet unknown mechanisms that prevent unrestricted direct signaling between endothelial and smooth muscle cells.     

Solubilization of V-ATPase transmembrane peptides by amphipol A8-35.

Two transmembrane peptides encompassing the seventh transmembrane section of subunit a from V-ATPase from Saccharomyces cerevisiae were studied as complexes with APols A8-35 by CD and fluorescence spectroscopy, with the goal to use APols to provide a membrane-mimicking environment for the peptides. CD spectroscopy was used to obtain the overall secondary structure of the peptides, whereas fluorescence spectroscopy provided information about the local environment of their tryptophan residues. The fluorescence results indicate that both peptides are trapped by APols and the CD results that they adopt a beta-sheet conformation. This result is in contrast with previous work that showed that the same peptides are alpha-helical in SDS micelles and organic solvents. These observations are discussed in the context of APol physical-chemical properties and transmembrane peptide structural propensity.     

The Effect of Chemical Information on the Spatial Distribution of Fruit Flies: I Model Results

Animal aggregation is a general phenomenon in ecological systems. Aggregations are generally considered as an evolutionary advantageous state in which members derive the benefits of protection and mate choice, balanced by the costs of limiting resources and competition. In insects, chemical information conveyance plays an important role in finding conspecifics and forming aggregations. In this study, we describe a spatio-temporal simulation model designed to explore and quantify the effects of these infochemicals, i.e., food odors and an aggregation pheromone, on the spatial distribution of a fruit fly (Drosophila melanogaster) population, where the lower and upper limit of local population size are controlled by an Allee effect and competition. We found that during the spatial expansion and strong growth of the population, the use of infochemicals had a positive effect on population size. The positive effects of reduced mortality at low population numbers outweighed the negative effects of increased mortality due to competition. At low resource densities, attraction toward infochemicals also had a positive effect on population size during recolonization of an area after a local population crash, by decreasing the mortality due to the Allee effect. However, when the whole area was colonized and the population was large, the negative effects of competition on population size were larger than the positive effects of the reduction in mortality due to the Allee effect. The use of infochemicals thus has mainly positive effects on population size and population persistence when the population is small and during the colonization of an area. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Energy Yield of Respiration on Chloroaromatic Compounds in Desulfitobacterium dehalogenans

The amount of energy that can be conserved via halorespiration by Desulfitobacterium dehalogenans JW/IU-DC1 was determined by comparison of the growth yields of cells grown with 3-chloro-4-hydroxyphenyl acetate (Cl-OHPA) and different electron donors. Cultures that were grown with lactate, pyruvate, formate, or hydrogen as an electron donor and Cl-OHPA as an electron acceptor yielded 3.1, 6.6, 1.6, and 1.6 g (dry weight) per mol of reduction equivalents, respectively. Fermentative growth on pyruvate yielded 14 g (dry weight) per mol of pyruvate oxidized. Pyruvate was not fermented stoichiometrically to acetate and lactate, but an excess of acetate was produced. Experiments with ¹³C-labeled bicarbonate showed that during pyruvate fermentation, approximately 9% of the acetate was formed from the reduction of CO₂. Comparison of the growth yields suggests that 1 mol of ATP is produced per mol of acetate produced by substrate-level phosphorylation and that there is no contribution of electron transport phosphorylation when D. dehalogenans grows on lactate plus Cl-OHPA or pyruvate plus Cl-OHPA. Furthermore, the growth yields indicate that approximately 1/3 mol of ATP is conserved per mol of Cl-OHPA reduced in cultures grown in formate plus Cl-OHPA and hydrogen plus Cl-OHPA. Because neither formate nor hydrogen nor Cl-OHPA supports substrate-level phosphorylation, energy must be conserved through the establishment of a proton motive force. Pyruvate ferredoxin oxidoreductase, lactate dehydrogenase, formate dehydrogenase, and hydrogenase were localized by in vitro assays with membrane-impermeable electron acceptors and donors. The orientation of chlorophenol-reductive dehalogenase in the cytoplasmic membrane, however, could not be determined. A model is proposed, which may explain the topology analyses as well as the results obtained in the yield study.     

Metaphors and the privileging of causes

With regard to the theoretical place of environmental factors in development, three approaches to evolution and development can be distinguished. One is the neo-Darwinist approach in which genetic programs are central. The other two present themselves as alternatives to the gene-centrism in present-day biology. I discuss pairwise similarities and differences between the three approaches. Goodwin's approach differs from neo-Darwinism in its favoured types of causes, but shares the internalist perspective on embryological development. The constructionist alternative proposes to enlarge the developmental system to include external factors, and shares with neo-Darwinism the emphasis on contingent causes. Thus there is neither a grand dichotomy in biology, between neo-Darwinism and its alternative, nor a grand trichotomy. Different purposes make different approaches useful. I conclude by arguing that environmental influences should have a more prominent place in developmental biology.