Self-organization of fairy circles
Fairy circle in the Western Australian outback.
Fairy circles are circular patches of bare soil in grasslands that form a uniform hexagonal pattern. Pattern-formation theory predicts that feedback between vegetation growth and water transport leads grasslands to self-organize into fairy circles, and that similar patterns might be a universal feature of arid ecosystems. However, fairy circles have previously been observed only in southwestern Africa. Stephan Getzin et al. (pp. 3551–3556) observed vegetation gaps resembling fairy circles in the Western Australian outback. Analysis of aerial photographs revealed that the patterns of Australian and African fairy circles have nearly identical features: highly regular hexagonal spacing at scales smaller than 50 m and homogeneous distribution at large scales. Field observations of Australian fairy circles indicated a substantial difference in soil physical properties and infiltration rates between the gaps and the surrounding vegetation. The observations suggest that rainwater falling on the gaps flows toward the vegetation as runoff, where it infiltrates the soil and promotes further vegetation growth. A mathematical model of vegetation growth, consistent with the field observations, reproduces the pattern of both Australian and African fairy circles. The results are consistent with the hypothesis that fairy circles arise from self-organization according to universal principles of pattern-formation theory, according to the authors. — B.D.
Light-sheet fluorescence nanoscopy by RESOLFT
Concept of light-sheet RESOLFT nanoscopy.
Light-sheet fluorescence microscopy involves illuminating a sample from the side with a laser beam focused into a sheet of light, thus optically sectioning the sample. The technique illuminates a thin z slice of the fluorescent sample and collects fluorescence perpendicularly. However, the extent of the sheet and resolution in the axial (z) direction are typically limited by diffraction. Patrick Hoyer et al. (pp. 3442–3446) describe reversible saturable/switchable optical (fluorescence) transitions (RESOLFT) light sheet (LS), a light-sheet nanoscope that offers improved resolution for 3D imaging via reversible switching between the fluorescent “on” state and a dark “off” state in entire 2D planes. In brief, a living specimen expressing reversibly switchable fluorescent proteins (RSFPs) is illuminated perpendicular to the detection axis. In a thin diffraction-limited section, RSFPs are switched from the off to the on state by a light sheet. A second light sheet switches off the activated RSFPs above and below the detection focal plane, whereas RSFPs in a slice of subdiffraction thickness remain on. A third light sheet reads the “on” fluorophores, contributing one piece to the LS-RESOLFT 3D image. The specimen platform is then moved and the process repeated until the 3D image is formed. Without the limit of diffraction, LS-RESOLFT can be developed for imaging at molecular-scale resolution, according to the authors. — L.G.
Tyrannosaur discovery illuminates dinosaur evolution
Horse-sized primitive tyrannosaur T. euotica from the Middle Cretaceous of Uzbekistan. Image courtesy of Todd Marshall.
Around 66–80 million years ago, the iconic Tyrannosaurus rex dominated the dinosaur group called tyrannosaurids. These apex predators rose to the top of the food chain by virtue of their massive size and well-developed senses. However, the tyrannosaur’s evolutionary path to dominance remains obscured by a 20-million-year gap in the fossil record. Stephen Brusatte et al. (pp. 3447–3452) describe a new species recovered from Uzbekistan that lived roughly 90 million years ago and that bridges the gap between the oldest, smallest known tyrannosauroids of the Early Cretaceous and the behemoths that thrived at the end of the Age of Dinosaurs. Based on a well-preserved braincase with tyrannosauroid features, the authors conclude that the species, dubbed Timurlengia euotica, possessed the signature brain and inner ear characteristics found in the latest Cretaceous tyrannosaurids. However, this midsized phylogenetic intermediate did not exhibit the tonnage of a tyrant lizard, weighing an estimated 170–270 kilograms. The authors caution that Timurlengia represents an individual find. According to the authors, tyrannosaurids may have ascended due to key brain and sensory innovations followed by rapid increases in body size. — T.J.
Overweight reporting in New York City schools
Schools in the United States are increasingly reporting body mass index (BMI) to students and their parents, but it is unclear whether such reports are effective in reducing obesity. Douglas Almond et al. (pp. 3488–3491) obtained more than 3.5 million BMI reports given to New York City public school students from 2007 to 2012, and examined how being classified as overweight for the previous academic year affected the students’ subsequent BMIs and weights. The authors compared female students whose BMI was close to their age-specific cutoff for being considered overweight with those whose BMI narrowly included them in the category considered healthy. The authors found that being labeled overweight had little to no effect on female students’ subsequent BMIs and weights, and these parameters did not decline relative to the healthy students when evaluated the following academic year. The authors found similar results when they examined the effects of being classified as obese; an analysis of male students also failed to find any effects of being labeled obese. The results indicate that being labeled overweight had no beneficial effects on the BMI of female students in New York City, compared with being categorized as healthy, and the authors suggest that overweight labels in the absence of additional services may not be an effective tool in curbing obesity. — S.R.
Network methods reveal plastid contribution to gene creation
Plastids, the photosynthetic organelles of algae and plants, are thought to have evolved via endosymbiosis between a free-living cyanobacterium and a eukaryotic host cell. Although this evolutionary relationship is well-known, researchers continue to unravel aspects of the integration of plastids and the breadth of their contributions to eukaryotic cells. Raphaël Méheust et al. (pp. 3579–3584) used network methods to detect gene fragments that the cyanobacterial endosymbiont contributed to new composite genes and determined the functions conferred by these novel genes. The authors found 67 qualifying nuclear gene families, at least 23 of which contributed directly to the evolution of photosynthesis in eukaryotes. Furthermore, the authors found that these previously unreported genes have emerged multiple, independent times during plastid evolution. Dubbed symbiogenetic genes, these composite genes contribute to reduction of oxidative stress damage, coordination of responses to light, and, potentially, the stabilization of the emerging host–endosymbiont relationship over time. The findings demonstrate that network methods can reveal symbiogenetic genes that have eluded detection using other methods as well as how photosynthetic eukaryotes recycle information to yield genetic innovations, according to the authors. — T.J.
Infants ask for help by communicating uncertainty
Infants nonverbally communicate uncertainty to others to fulfill goals.
Animals ranging from insects to primates monitor internal levels of uncertainty to optimize decision-making strategies. Humans are the only species known to explicitly communicate uncertainty to others, but whether this unique capacity arises early in development or after language acquisition remains unclear. Louise Goupil et al. (pp. 3492–3496) tested whether 80 20-month-old human infants would ask for help to avoid making mistakes in a nonverbal memory task. The infants had to remember the location of a toy hidden under one of two boxes placed on a table. After a variable delay ranging from 3–12 seconds, the infants were asked to point to the box containing the toy. During trials designated “possible,” infants saw the experimenter place the toy under the box, but during trials designated “impossible,” the toy was hidden out of view behind a curtain. The infants specifically asked for help by looking at their parents in the eyes to avoid pointing to the wrong location. Such nonverbal communication of uncertainty was more likely during impossible trials than during possible trials, and for trials with long memorization delays than those with short delays. According to the authors, young children monitor internal levels of uncertainty and nonverbally share this information with others to successfully accomplish difficult tasks. — J.W.