The role of iron in the formation of Ediacaran ‘death masks’

The Ediacara biota are an enigmatic group of Neoproterozoic soft-bodied fossils that mark the first major radiation of complex eukaryotic and macroscopic life. These fossils are thought to have been preserved via pyritic “death masks” mediated by seafloor microbial mats, though little about the chemical constraints of this preservational pathway is known, in particular surrounding the role of bioavailable iron in death mask formation and preservational fidelity. In this study, we perform decay experiments on both diploblastic and triploblastic animals under a range of simulated sedimentary iron concentrations, in order to characterize the role of iron in the preservation of Ediacaran organisms. After 28 days of decay, we demonstrate the first convincing “death masks” produced under experimental laboratory conditions composed of iron sulfide and probable oxide veneers. Moreover, our results demonstrate that the abundance of iron in experiments is not the sole control on death mask formation, but also tissue histology and the availability of nucleation sites. This illustrates that Ediacaran preservation via microbial death masks need not be a “perfect storm” of paleoenvironmental porewater and sediment chemistry, but instead can occur under a range of conditions.     

The ‘Embryonic moults’ of the milkweed bug as seen by the S.E.M.

Deposition, detachment and removal of the three embryonic cuticles are studied. The menbrane-like cuticle 1 covers the embryo during katatrepsis and ‘disappears’ thereafter. Cuticle 2 deposition starts shortly before dorsal closure. Its apolysis is accompanied by contractions of the embryo. Ecdysis of cuticle 2 takes place during hatching. Only cuticle 3 (= first larval cuticle) shows differentiations like sensilla and cornea. Peaks of ecdysteroid (and probably JH) titre are observed during apolysis of cuticle 1 and cuticle 2 (Dorn, 1981). Transition from ectoderm to epidermis proper takes place shortly before and during onset of cuticle 2 synthesis.     

The role of the shrub Cordia multispicata Cham. as a ‘succession facilitator’ in an abandoned pasture,Paragominas, Amazônia

We studied the conditions that permit the shrub, Cordia multispicata, to establish in Amazon pastures and the potential role of this shrub as a succession facilitator near the town of Paragominas, Pará State, Brazil. Local disturbances that reduce cover such as grazing and burning helped C. multispicata establish in pastures in active use. Germination of C. multispicata was significantly improved on sites subjected to simulated grazing and seedling growth was hastened following pasture burning. We found that below-ground competition, evaluated using root ingrowth cores, was reduced by burning and grazing. Recently abandoned pastures are frequently composed of a mix of forbs and grasses but as succession proceeds a mosaic of more discrete vegetation patches appears. At our site, a five-year-old abandoned pasture, grass patches (primarily Panicum maximum) and shrub patches (mainly C. multispicata) were common. We compared physical and biotic characteristics of zones dominated by C. multispicata and P. maximum and found: (1) the rain of bat and bird dispersed seeds of woody species was much greater in the zones of C. multispicata (92 seeds/m²/year) than in the patches of grass (6 seeds/m²/year); (2) the density of woody seedlings was eight times greater in the C. multispicata patches (0.65/m²) than in the zones of P. maximum (0.08 woody individuals/m²); (3) soil nutrient availability and litter nutrient concentrations were greater in the shrub zones than in the grass zones; and (4) photosynthetic photon flux density at the soil surface was generally more favorable for rainforest tree seedling growth in C. multispicata patches (16% of full sunlight) as compared to the grass zones (7.7% of full sun). We conclude that the shrub, C. multispicata, acts as a magnet, attracting volant seed vectors, and as a nurse plant, facilitating the establishment of woody species in abandoned Amazon pastures.     

The ‘true’ growth efficiency of phytoplankton as influenced by light attenuation and insolation: implications of the photosynthesis-irradiance relationship

The true growth efficiency (c) relates the light energy absorbed by phytoplankton to the production of biomass corrected for constant energy requirement of maintenance. Continuous culture studies have shown that, at constant incident irradiance, the value of c for both prokaryotic and eukaryotic species is constant. Culture data for the relevant conditions of incident light may be used for directly estimating the growth rate from daily insolation of optically deep, fully mixed lakes, when the light absorption by the phytoplankton can be established. In order to examine the influence of vertical light attenuation and daily insolation on c, computations were made on a basis of a photosynthesis-irradiance curve of light-limited Oscillatoria limnetica. For steady state growth, the true growth efficiency is linearly related to the areal quantum efficiency of photosynthesis ( _a ). The computations showed that _a remains constant at fluctuating vertical light attenuation, no matter whether the concentration of tripton or phytoplankton changes. The effect of insolation is great: _a is 0.108 mol O₂/E at very low light, but only 0.014 mol O₂/E at 400 W m^–2 subsurface downward irradiance. The results imply that a c-value obtained from cultures for summer averaged insolation must be corrected: between cloudy and clear days the value may vary by a factor of 2. The true growth efficiency for cultures will decrease by about 10% when the same daily irradiation is dosed sinusoidally instead of constantly.     

Worth the ‘EEfRT’? The Effort Expenditure for Rewards Task as an Objective Measure of Motivation and Anhedonia

Background

Of the putative psychopathological endophenotypes in major depressive disorder (MDD), the anhedonic subtype is particularly well supported. Anhedonia is generally assumed to reflect aberrant motivation and reward responsivity. However, research has been limited by a lack of objective measures of reward motivation. We present the Effort-Expenditure for Rewards Task (EEfRT or “effort”), a novel behavioral paradigm as a means of exploring effort-based decision-making in humans. Using the EEfRT, we test the hypothesis that effort-based decision-making is related to trait anhedonia.

Methods/Results

61 undergraduate students participated in the experiment. Subjects completed self-report measures of mood and trait anhedonia, and completed the EEfRT. Across multiple analyses, we found a significant inverse relationship between anhedonia and willingness to expend effort for rewards.

Conclusions

These findings suggest that anhedonia is specifically associated with decreased motivation for rewards, and provide initial validation for the EEfRT as a laboratory-based behavioral measure of reward motivation and effort-based decision-making in humans.     

The formation of cholest-5-ene-3β,26-diol as an intermediate in the conversion of cholesterol into bile acids by liver mitochondria

1. When [(14)C]cholesterol was incubated with rat liver mitochondria, radioactive 26-hydroxycholesterol, 3beta-hydroxychol-5-enoic acid and other bile acids were isolated from the incubation mixture. 2. In the absence of added 26-hydroxycholesterol, the specific radioactivity of the 26-hydroxycholesterol formed from [(14)C]cholesterol during the incubation was higher than that of the 3beta-hydroxychol-5-enoic acid. Addition of increasing amounts of 26-hydroxycholesterol led to a progressive fall in the specific radioactivity, and to a progressive increase in the mass, of the 3beta-hydroxychol-5-enoic acid recovered at the end of the incubation. 3. It is concluded that 26-hydroxycholesterol is an intermediate in the formation of 3beta-hydroxychol-5-enoic acid from cholesterol. 4. Comparison of the specific radioactivity of the 26-hydroxycholesterol formed in the incubation mixture with that of the added [(14)C]cholesterol indicates that endogenous cholesterol in mitochondria is accessible to cholesterol 26-hydroxylase.     

‘The vain speculation disillusioned by the sense’: the Italian painter Agostino Scilla (1629–1700) called ‘The Discoloured’, and the correct interpretation of fossils as ‘lithified organisms’ that once lived in the sea

The search for the true nature and origin of fossils gave rise, starting about the beginning of the sixteenth century and throughout the seventeenth century, to a heated debate between the supporters of the inorganic nature of these objects and proponents of an interpretation of fossils as ex-vivi. Among the latter, a key figure is the Italian painter Agostino Scilla (1629–1700), who represents one of the first naturalists who was able to accumulate substantial evidence to support the interpretation of fossils as once-living marine organisms. The world view of Scilla and his real contribution to paleontology are here analysed and contextualised, taking into account the state of knowledge characterising the time of his activities. Scilla was not only a pioneer in the field of paleontology, but he prepared the groundwork for the achievement of milestone geological concepts such as actualism, taphonomy and recognition of internal and external moulds (in the instance of non-representation of original hard parts); Scilla deserves further recognition as one of the first to attempt sedimentological interpretation of rocky bodies observed directly in the field.     

The effect of total inorganic nitrogen and the balance between its ionic forms on adventitious bud formation and callus growth of ‘Węgierka Zwykła’ plum (<Emphasis Type="Italic">Prunus domestica</Emphasis> L.)

The effect of different ammonium NH ₄ ⁺ and nitrate NO ₃ ^? ratios (4:1, 2:1, 1:1, 1:2, 1:4, 1:6) on organogenesis of ‘W?gierka Zwyk?a’ leaf explants cultivated on media with nitrogen levels equalling full- or half-MS was investigated. On media with total nitrogen equal to ½ MS, explant regeneration increased significantly and was highest on media with 1:2 or 1:4 NH ₄ ⁺ :NO ₃ ^? ratio. An excess of ammonium versus nitrate ions had a negative effect on both regeneration and biomass. Addition of potassium to the medium increased the fresh weight of explants and the number of adventitious buds.