How the Venus flytrap snaps

The rapid closure of the Venus flytrap (Dionaea muscipula) leaf in about 100 ms is one of the fastest movements in the plant kingdom. This led Darwin to describe the plant as "one of the most wonderful in the world". The trap closure is initiated by the mechanical stimulation of trigger hairs. Previous studies have focused on the biochemical response of the trigger hairs to stimuli and quantified the propagation of action potentials in the leaves. Here we complement these studies by considering the post-stimulation mechanical aspects of Venus flytrap closure. Using high-speed video imaging, non-invasive microscopy techniques and a simple theoretical model, we show that the fast closure of the trap results from a snap-buckling instability, the onset of which is controlled actively by the plant. Our study identifies an ingenious solution to scaling up movements in non-muscular engines and provides a general framework for understanding nastic motion in plants.     

The incomplete beta function — a historical profile

Summary A history of the development of the incomplete beta function is outlined as well as of some of the analytical and approximation techniques used for its numerical evaluation. Dedicated to W. Edwards Deming, my teacher and my friend     

Antipredatory defense of neonatal pronghorn ( Antilocapra americana ) by yearling male pronghorn in southwestern South Dakota

Antipredatory defense of pronghorn ( Antilocapra americana ) neonates (≤1 month old) by adult females (>18 months old) is well documented throughout the geographic range of this species. However, reports of male pronghorn defending neonates against predators are limited to a single study in northwestern Wyoming where occurrences were documented of adult males assisting female pronghorn in defending neonates against coyotes ( Canis latrans ). To our knowledge, defense of neonatal pronghorn by yearling males (12–18 months old) has not been reported previously for this species. We report occurrences of antipredatory defense of neonatal pronghorn by yearling males in southwestern South Dakota. La defensa antidepredadora de los neonatos (≤30 días de edad) del berrendo ( Antilocapra americana ) por hembras adultas (>18 meses de edad) está bien documentada en toda la distribución geográfica de esta especie. Sin embargo, no se había reportado la defensa de neonatos contra depredadores por parte de berrendos machos con excepción de un solo estudio en el noroeste de Wyoming, donde documentaron algunos casos en los que machos adultos ayudaron a los berrendos hembras a defender los neonatos contra coyotes ( Canis latrans ). Hasta donde sabemos, la defensa de berrendos neonatales por machos de alrededor de un año de edad (de 12–18 meses de edad) no se había reportado previamente. Reportamos casos de defensa antidepredadora de berrendos neonatales por parte de machos de un año de edad en el suroeste de Dakota del Sur.     

The auroral footprint of Enceladus on Saturn

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity.     

Ocean-like water in the Jupiter-family comet 103P/Hartley 2

For decades, the source of Earth's volatiles, especially water with a deuterium-to-hydrogen ratio (D/H) of (1.558?±?0.001)?×?10(-4), has been a subject of debate. The similarity of Earth's bulk composition to that of meteorites known as enstatite chondrites suggests a dry proto-Earth with subsequent delivery of volatiles by local accretion or impacts of asteroids or comets. Previous measurements in six comets from the Oort cloud yielded a mean D/H ratio of (2.96?±?0.25)?×?10(-4). The D/H value in carbonaceous chondrites, (1.4?±?0.1)?×?10(-4), together with dynamical simulations, led to models in which asteroids were the main source of Earth's water, with ≤10 per cent being delivered by comets. Here we report that the D/H ratio in the Jupiter-family comet 103P/Hartley 2, which originated in the Kuiper belt, is (1.61?±?0.24)?×?10(-4). This result substantially expands the reservoir of Earth ocean-like water to include some comets, and is consistent with the emerging picture of a complex dynamical evolution of the early Solar System.     

Cell attachment protein VP8* of a human rotavirus specifically interacts with A-type histo-blood group antigen

As with many other viruses, the initial cell attachment of rotaviruses, which are the major causative agent of infantile gastroenteritis, is mediated by interactions with specific cellular glycans. The distally located VP8* domain of the rotavirus spike protein VP4 (ref. 5) mediates such interactions. The existing paradigm is that 'sialidase-sensitive' animal rotavirus strains bind to glycans with terminal sialic acid (Sia), whereas 'sialidase-insensitive' human rotavirus strains bind to glycans with internal Sia such as GM1 (ref. 3). Although the involvement of Sia in the animal strains is firmly supported by crystallographic studies, it is not yet known how VP8* of human rotaviruses interacts with Sia and whether their cell attachment necessarily involves sialoglycans. Here we show that VP8* of a human rotavirus strain specifically recognizes A-type histo-blood group antigen (HBGA) using a glycan array screen comprised of 511 glycans, and that virus infectivity in HT-29 cells is abrogated by anti-A-type antibodies as well as significantly enhanced in Chinese hamster ovary cells genetically modified to express the A-type HBGA, providing a novel paradigm for initial cell attachment of human rotavirus. HBGAs are genetically determined glycoconjugates present in mucosal secretions, epithelia and on red blood cells, and are recognized as susceptibility and cell attachment factors for gastric pathogens like Helicobacter pylori and noroviruses. Our crystallographic studies show that the A-type HBGA binds to the human rotavirus VP8* at the same location as the Sia in the VP8* of animal rotavirus, and suggest how subtle changes within the same structural framework allow for such receptor switching. These results raise the possibility that host susceptibility to specific human rotavirus strains and pathogenesis are influenced by genetically controlled expression of different HBGAs among the world's population.