Gestagens and glucocorticoids in chicken eggs

Avian eggs contain a variety of steroid hormones, which have been attributed as a tool for maternal phenotypic engineering. The majority of studies focuses on androgens, but also significant amounts of progesterone as well as other steroid hormones have been measured. The question if corticosterone is also present in eggs of chickens is currently under debate. The only analytical validation performed so far has failed to demonstrate corticosterone in the yolk of chickens, suggesting that antibodies for corticosterone measurement cross-react with other steroids present in the yolk. In order to investigate this assumption and to characterise potential cross-reacting hormones in more detail, we performed high-performance liquid chromatographic (HPLC) analyses of chicken yolk extracts and determined the concentration of immunoreactive corticosterone, progesterone and cortisol. The progesterone antibody revealed several immunoreactive substances, including progesterone, pregnenolone and two substances with lower polarity. The corticosterone enzyme immunoassay detected immunoreactive substances at exactly the same elution positions as the progesterone assay and a very small peak at the elution position of corticosterone. Immunoreactive cortisol was not found. In addition, inner and outer regions of the yolk sphere were analysed separately via HPLC. We found different concentrations of immunoreactive substances between the inner and outer yolk regions, probably reflecting the steroidogenic activity of the follicle cells during oocyte growth. We conclude that in homogenised yolk extracts without previous clean-up, the measured corticosterone concentrations may actually reflect those of progesterone and its precursors, most probably being 5 alpha- and 5 beta-pregnanes and pregnenolone. (C) 2009 Elsevier Inc. All rights reserved

Geographical Variation in Egg Mass and Egg Content in a Passerine Bird

Reproductive, phenotypic and life-history traits in many animal and plant taxa show geographic variation, indicating spatial variation in selection regimes. Maternal deposition to avian eggs, such as hormones, antibodies and antioxidants, critically affect development of the offspring, with long-lasting effects on the phenotype and fitness. Little is however known about large-scale geographical patterns of variation in maternal deposition to eggs. We studied geographical variation in egg components of a passerine bird, the pied flycatcher (Ficedula hypoleuca), by collecting samples from 16 populations and measuring egg and yolk mass, albumen lysozyme activity, yolk immunoglobulins, yolk androgens and yolk total carotenoids. We found significant variation among populations in most egg components, but ca. 90% of the variation was among individuals within populations. Population however explained 40% of the variation in carotenoid levels. In contrast to our hypothesis, we found geographical trends only in carotenoids, but not in any of the other egg components. Our results thus suggest high within-population variation and leave little scope for local adaptation and genetic differentiation in deposition of different egg components. The role of these maternally-derived resources in evolutionary change should be further investigated.Peer reviewe

Fecal corticosteroids in a territorial bird selected for different personalities:daily rhythm and the response to social stress

In this study we tested the hypothesis that in a passerine bird (great tit, Parus major) individuals differing for coping strategies differ in the magnitude of the adrenocortical response to social stress as well. Furthermore, we aimed at characterizing daily rhythms in corticosteroid release before and after social stress. We used 16 males from either of two lines bidirectionally selected for different coping strategies (fast and slow explorers). Social stress was induced by confrontation with an aggressive resident male. Corticosteroid metabolites were analyzed in feces collected at 90-min intervals from 900 to 1630 h on a baseline day, on the day of the social conflict, and on the following day. In both days and in both lines levels varied with time of day in a robust rhythm with a peak in the first sample of the morning and a trough at the end of the light phase. This rhythm correlates with activity (perch hopping). An overall increase in levels relative to baseline day was observed between 30 and 140 min after the challenge. Birds of the less aggressive and more cautious line (slow explorers) showed a trend for a higher response compared to birds of the more aggressive and bolder line (fast explorers), which showed almost no response. On the day after the challenge the birds of the slow line exhibited significantly reduced corticosteroid secretion, probably due to an increased negative feedback. The results provide evidence for a physiological basis of different coping strategies in birds, emerging in response to social stress and with a pattern similar to that in other vertebrates. (C) 2003 Elsevier Science (USA). All rights reserved

Corticosterone in bird eggs:The importance of analytical validation

<p>It was recently found that high concentrations of chicken yolk gestagens and gestagen metabolites hamper corticosterone quantification via immunoassays. However, the situation in chicken albumen is still unresolved. In addition, the ratio of steroid hormone in the yolk of wild birds might differ. To investigate these matters, corticosterone and gestagens were measured in individual fractions of high-performance liquid-chromatographic separations of chicken albumen and yolk of red jungle fowl. Similarly, yolk extracts of hens with corticosterone-releasing implants or placebos were analysed to assess the impact of elevated plasma corticosterone concentrations on authentic yolk corticosterone levels. We also compared the results of a previously used corticosterone enzyme immunoassay (EIA) to those from a commercial radioimmunoassay (RIA) kit. The analytical validations of chicken albumen, bankiva yolk and yolks from hens with or without artificially elevated plasma corticosterone levels indicated that the main share of the immunoreactivity measured via corticosterone immunoassays was caused by substances other than authentic corticosterone. In albumen, the concentration of authentic corticosterone was below the detection limit. Analysis of bankiva yolk revealed three major gestagen peaks with concentrations of up to 2000 ng per fraction and a corticosterone peak of about 0.8 ng per fraction. Both corticosterone assays found a slightly higher corticosterone peak in a corticosterone-implanted hen's yolk (EIA: 0.7 ng; RIA: 0.5 ng per fraction) compared to the sham-treated female (EIA: 0.5 ng; RIA: 0.2 ng per fraction) but both antibodies also bound to several other substances, presumably gestagens. Although a certain amount of circulating corticosterone might pass into the yolk, direct quantification of corticosterone in non-homogenized avian egg samples via immunoassays is not advisable.</p>

First observations of magnetic holes deep within the coma of a comet

The Rosetta spacecraft of the European Space Agency made ground-breaking observations of comet 67P/Churyumov-Gerasimenko and of its cometary environment. We search for magnetic holes in that environment, i.e., significant depressions in the magnetic field strength, measured by the Rosetta fluxgate Magnetometer (MAG) in April and May 2015. In that time frame of two months, we identified 23 magnetic holes. The cometary activity was intermediate and increasing because Rosetta was on the inbound leg toward the Sun. While in April solar wind protons were still observed by Rosetta near the comet, in May these protons were already mostly replaced by heavy cometary ions. Magnetic holes have frequently been observed in the solar wind. We find, for the first time, that magnetic holes exist in the cometary environment even when solar wind protons are almost absent. Some of the properties of the magnetic holes are comparable to those of solar wind holes; they are associated with density enhancements, sometimes associated with co-located current sheets and fast solar wind streams, and are of similar scales. However, particularly in May, the magnetic holes near the comet appear to be more processed, featuring shifted density enhancements and, sometimes, bipolar signatures in magnetic field strength rather than simple depressions. The magnetic holes are of global size with respect to the coma. However, at the comet, they are compressed owing to magnetic field pile-up and draping so that they change in shape. There, the magnetic holes become of comparable size to heavy cometary ion gyroradii, potentially enabling kinetic interactions

Unchanged cerebrovascular CO₂ reactivity and hypercapnic ventilatory response during strict head-down tilt bed rest in a mild hypercapnic environment

Chronically elevated carbon dioxide (CO₂) levels can occur in confined spaces such as the International Space Station. Using the spaceflight analogue 30 days of strict 6° head-down tilt bed rest (HDTBR) in a mild hypercapnic environment ( PCO₂ = 4 mmHg), we investigated arterialized PCO₂, cerebrovascular reactivity and the hypercapnic ventilatory response in 11 healthy subjects (five females) before, on days 1, 9, 15 and 30 of bed rest (BR), and 6 and 13 days after HDTBR. During all HDTBR time points, arterialized PCO₂ was not significantly different from the pre-HDTBR measured in the 6° HDT posture, with a mean (95% confidence interval) increase of 1.2 mmHg (–0.2 to 2.5 mmHg, P = 0.122) on day 30 of HDTBR. Respiratory acidosis was never detected, although a mild metabolic alkalosis developed on day 30 of HDTBR by a mean (95% confidence interval) pH change of 0.032 (0.022–0.043; P < 0.001), which remained elevated by 0.021 (0.011–0.031; P < 0.001) 6 days after HDTBR. Arterialized pH returned to pre-HDTBR levels 13 days after BR with a change of –0.001 (–0.009 to 0.007; P = 0.991)