Sex-specific effects of yolk-androgens on growth of nestling American kestrels

Maternally derived androgen hormones concentrate in avian egg yolks as the yolks grow on the female’s ovary, possibly forming a basis for important maternal effects in birds. In the American kestrel (Falco sparverius), experimental elevation of yolk androgens in the first-laid egg of a clutch (a-egg) to the concentrations found naturally in a clutch’s later-laid eggs reduces the growth rate of a-egg nestlings compared to controls. These findings, together with discoveries from other species that the effects of yolk androgens on growth of female nestlings may differ from their effects on growth of male nestlings, raise the hypothesis that natural changes in yolk-androgen concentrations with laying order are ultimately due to a difference between the sexes in their yolk-androgen sensitivity and between early- and late-laid eggs in their sex ratio. By re-analyzing previously published data and adding to the analysis data from previously unanalyzed blood samples used for sex determination, we investigated possible sex-specific effects of yolk-androgens in the context of a potential sex-biased laying order in free-living American kestrels. We used a multi-level, mixed model with a Gompertz function to analyze growth of nestlings hatching from a-eggs that were control-treated or in which we experimentally elevated yolk-androgen concentrations shortly after laying to the higher concentrations naturally found in later-laid eggs. We discovered that male nestlings were more susceptible than female nestlings to growth inhibition by yolk-androgen elevation but did not find a bias in sex ratio with respect to laying order. Together, these findings do not support the above hypothesis. However, they are consistent with the hypothesis that sex differences in yolk-androgen sensitivity enable mothers to economically tune reproductive effort to an individual offspring’s reproductive value, which can vary more for one sex than the other.     

Dominance of the odometer over serial landmark learning in honeybee navigation

Honeybees use their visual flow field to measure flight distance. It has been suggested that the experience of serial landmarks encountered on the flight toward a feeding place contributes to distance estimation. Here, we address this question by tracing the flight paths of individual bees with a harmonic radar system. Bees were trained along an array of three landmarks (tents), and the distance between these landmarks was either increased or decreased under two test conditions. We find that absolute distance estimation dominates the search for the feeding place, but serial position effects are also found. In the latter case, bees search only or additionally at locations determined by serial experience of the landmarks.     

Visualizing different uranium oxidation states during the surface alteration of uraninite and uranium tetrachloride

Low-temperature alteration reactions on uranium phases may lead to the mobilization of uranium and thereby poses a potential threat to humans living close to uranium-contaminated sites. In this study, the surface alteration of uraninite (UO₂) and uranium tetrachloride (UCl₄) in air atmosphere was studied by confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy using an excitation wavelength of 408 nm. It was found that within minutes the oxidation state on the surface of the uraninite and the uranium tetrachloride changed. During the surface alteration process U(IV) atoms on the uraninite and uranium tetrachloride surface became stepwise oxidized by a one-electron step at first to U(V) and then further to U(VI). These observed changes in the oxidation states of the uraninite surface were microscopically visualized and spectroscopically identified on the basis of their fluorescence emission signal. A fluorescence signal in the wavelength range of 415–475 nm was indicative for metastable uranium(V), and a fluorescence signal in the range of 480–560 nm was identified as uranium(VI). In addition, the oxidation process of tetravalent uranium in aqueous solution at pH 0.3 was visualized by CLSM and U(V) was fluorescence spectroscopically identified. The combination of microscopy and fluorescence spectroscopy provided a very convincing visualization of the brief presence of U(V) as a metastable reaction intermediate and of the simultaneous coexistence of the three states U(IV), U(V), and U(VI). These results have a significant importance for fundamental uranium redox chemistry and should contribute to a better understanding of the geochemical behavior of uranium in nature. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.