Optimal traffic organization in ants under crowded conditions

Efficient transportation, a hot topic in nonlinear science, is essential for modern societies and the survival of biological species. Biological evolution has generated a rich variety of successful solutions, which have inspired engineers to design optimized artificial systems. Foraging ants, for example, form attractive trails that support the exploitation of initially unknown food sources in almost the minimum possible time. However, can this strategy cope with bottleneck situations, when interactions cause delays that reduce the overall flow? Here, we present an experimental study of ants confronted with two alternative routes. We find that pheromone-based attraction generates one trail at low densities, whereas at a high level of crowding, another trail is established before traffic volume is affected, which guarantees that an optimal rate of food return is maintained. This bifurcation phenomenon is explained by a nonlinear modelling approach. Surprisingly, the underlying mechanism is based on inhibitory interactions. It points to capacity reserves, a limitation of the density-induced speed reduction, and a sufficient pheromone concentration for reliable trail perception. The balancing mechanism between cohesive and dispersive forces appears to be generic in natural, urban and transportation systems.     

The morphological and functional variability of pleon-holding mechanisms in selected Eubrachyura (Crustacea: Decapoda)

Eubrachyurans not only exhibit a crab-like body shape, consisting of a mostly wide cephalothorax and a thin, shield-like pleon folded underneath it, but reportedly hold the pleon in this position with the use of specialized holding structures. To further our knowledge of the variability of these holding structures, and investigate their functionality, male and female crabs from five primary freshwater crab and five selected thoracotreme families were examined with stereomicroscopy. Exemplary specimens of each group were documented photographically and with micro-computed tomography to illustrate the holding structures in situ. The results show a press-button mechanism of variable shape in freshwater crabs, where divergent structures possibly support pleon attachment of different effectiveness. The press-button is present in the majority of basal heterotreme lineages, and is therefore regarded as an ancestral character of the Heterotremata. In the Thoracotremata, multiple holding mechanisms are identified: press-button, clasping apparatus, overhanging edge, and increased setae cover on sternal plates, with the last system probably only effective in terrestrial species, due to wet adhesion effects. The ancestral character state in the Thoracotremata is debatable, but most likely also a functional press-button was present. Each holding mechanism requires different pleon movements to engage and disengage. Additionally, in contrast to the most common press-button mechanism, divergent holding mechanisms tend to be present, and likely functional, in adult males and females.     

Do Media Data Help to Predict German Industrial Production?

In an uncertain world, decisions by market participants are based on expectations. Therefore, sentiment indicators reflecting expectations have a proven track record at predicting economic variables. However, survey respondents largely perceive the world through media reports. Here, we want to make use of that. We employ a rich dataset provided by Media Tenor International, based on sentiment analysis of opinion‐leading media in Germany from 2001 to 2014, transformed into several monthly indices. German industrial production is predicted in a real‐time out‐of‐sample forecasting experiment and media indices are compared to a huge set of alternative indicators. Media data turn out to be valuable for 10‐ to 12‐month horizon forecasts, which is in line with the lag between monetary policy announcements and their effect on industrial production. This holds in the period during and after the Great Recession when many models fail. Copyright © 2016 John Wiley & Sons, Ltd.     

Distribution, silencing potential and evolutionary impact of promoter DNA methylation in the human genome

To gain insight into the function of DNA methylation at cis-regulatory regions and its impact on gene expression, we measured methylation, RNA polymerase occupancy and histone modifications at 16,000 promoters in primary human somatic and germline cells. We find CpG-poor promoters hypermethylated in somatic cells, which does not preclude their activity. This methylation is present in male gametes and results in evolutionary loss of CpG dinucleotides, as measured by divergence between humans and primates. In contrast, strong CpG island promoters are mostly unmethylated, even when inactive. Weak CpG island promoters are distinct, as they are preferential targets for de novo methylation in somatic cells. Notably, most germline-specific genes are methylated in somatic cells, suggesting additional functional selection. These results show that promoter sequence and gene function are major predictors of promoter methylation states. Moreover, we observe that inactive unmethylated CpG island promoters show elevated levels of dimethylation of Lys4 of histone H3, suggesting that this chromatin mark may protect DNA from methylation.     

The first vertebrate fossil from Socotra Island (Yemen) is an early Holocene Egyptian fruit bat

Data on the prehistoric biota of the Socotra Archipelago (Yemen) are scarce. We report on the first extinct vertebrate ever recorded from this western Indian Ocean island group. An exceptionally preserved adult specimen of Egyptian fruit bat Rousettus aegyptiacus was found in a calcite flowstone in Hoq Cave on the NE coast of Socotra Island. Accelerator mass spectrometry (AMS) radiocarbon dating on bone fragments estimates the fossil at ca. 7600–7400 cal a BP (radiocarbon age 6669 ± 70 ¹⁴C a BP) corresponding to an early Holocene wet period in southern Arabia and the Horn of Africa. Morphometric analysis of the skull compared to Recent specimens from the neighbouring mainlands finds the fossil morphologically most similar to Egyptian (Nile Valley and Libyan Desert), not to East African or Middle Eastern populations. The species is currently absent from the Horn of Africa (Somalia and Eastern Ethiopia). Although potentially a stray individual, we also discuss the palaeoenvironmental implications under the hypothetical scenario that the fruit bat is a remnant of an extinct resident population. If so, the extinction of an important pollinator and seed disperser may have impacted the Socotran terrestrial ecosystems.     

Gadd45a promotes epigenetic gene activation by repair-mediated DNA demethylation

DNA methylation is an epigenetic modification that is essential for gene silencing and genome stability in many organisms. Although methyltransferases that promote DNA methylation are well characterized, the molecular mechanism underlying active DNA demethylation is poorly understood and controversial. Here we show that Gadd45a (growth arrest and DNA-damage-inducible protein 45 alpha), a nuclear protein involved in maintenance of genomic stability, DNA repair and suppression of cell growth, has a key role in active DNA demethylation. Gadd45a overexpression activates methylation-silenced reporter plasmids and promotes global DNA demethylation. Gadd45a knockdown silences gene expression and leads to DNA hypermethylation. During active demethylation of oct4 in Xenopus laevis oocytes, Gadd45a is specifically recruited to the site of demethylation. Active demethylation occurs by DNA repair and Gadd45a interacts with and requires the DNA repair endonuclease XPG. We conclude that Gadd45a relieves epigenetic gene silencing by promoting DNA repair, which erases methylation marks.