Rapid warming and mass mortality of fish
A dead lionfish floating near the surface above the coral reef of Eilat, Gulf of Aqaba, in summer 2017.
Studies of the ecological impacts of ocean warming have traditionally focused on the duration and maximum temperatures of warming events, but not on the rate of warming. Amatzia Genin et al. (pp. 25378–25385) examined the mass mortality of fish that occurred in the northern Red Sea following two rapid warming events in July 2017. During both events, temperatures rose by more than 3 °C in 2.5 days, although the maximum temperatures reached were well within the normal temperature range for the season. For 10 weeks following the initial warming event, hundreds of fish carcasses were collected along the coast near Eilat, Israel. Necropsies performed on moribund and freshly dead specimens revealed infection by Streptococcus iniae, a ubiquitous bacterial pathogen of fish, in nearly all cases. Piscivorous and benthic grazing species, such as groupers and parrotfish, were disproportionately represented among the carcasses, suggesting that the infection likely spread through consumption of infected fish and their carcasses. The authors reexamined two earlier documented mass fish kills, in Kuwait Bay in 2001 and western Australia in 2011, and found that both were immediately preceded by rapid warming spikes. The results suggest that the rapid onset of warming, regardless of the final temperature attained, might trigger widespread mortality of coral reef fish, according to the authors. — B.D.
Mortality burden from air pollution in and around China
County-level premature deaths attributable to long-term PM2.5 exposures in China in 2000 and 2010. The box shows the islands in the South China Sea.
The mortality burden from fine particulate matter (PM2.5) exposure is difficult to assess due to limited data of long-term exposure. To determine PM2.5 concentration trends and associated mortality burdens in Mainland China, Hong Kong, Macao, and Taiwan between 2000 and 2016, Fengchao Liang et al. (pp. 25601–25608) combined satellite data with air pollution emission indicators as well as data on land cover, meteorological conditions, and road networks. Beijing, Tianjin, and southern Hebei experienced the highest concentrations of PM2.5, whereas relatively low concentrations were found in the rural areas of northern Inner Mongolia, southeastern Tibet, and western Sichuan. The lowest PM2.5 levels occurred in 2000, although levels peaked in 2013 before declining through 2016. Whereas the highest per-capita deaths in China occurred in Hebei, Henan, Shandong, and Tianjin, the lowest per-capita deaths occurred in Hainan, Macao, and Taiwan. Decreased PM2.5 concentration levels were correlated with decreased annual mortality burdens in 2013 through 2016. Overall, long-term exposure to PM2.5 accounted for 30.8 million premature deaths of individuals at least 25 years of age between 2000 and 2016, with the annual mortality burden ranging from 1.5 million to 2.2 million deaths. The findings highlight the need for assessing health effects attributed to air pollution in highly polluted regions, according to the authors. — M.S.
Burned organic matter in the Chicxulub impact
A large asteroid (∼12 km in diameter) hit Earth 66 million years ago, likely causing the end-Cretaceous mass extinction. Image credit: Southwest Research Institute/Don Davis.
Geologic records of the impact of an asteroid in the Yucatán Peninsula that likely initiated the end-Cretaceous extinction include markers of burned organic matter, the source of which was previously unclear. Shelby Lyons et al. (pp. 25327–25334) analyzed three sedimentary sequences from the impact event to characterize the sources and potential implications of the burn markers, which are composed of polycyclic aromatic hydrocarbons (PAHs). PAH chemical signatures suggest that the initial release of black carbon came from a fossil source rather than from global wildfires and had experienced rapid heating, consistent with rock material ejected during the asteroid impact. The authors estimate that between 7.5 x 1014 and 2.5 x 1015 g of black carbon was ejected from the crater and dispersed in the atmosphere immediately following the impact. Charcoal was also present in the samples, indicating that wildfires following the impact were likely delayed and protracted relative to the formation of black carbon burn markers and that the wildfires’ contribution to the impact winter and subsequent extinction may have been smaller than thought. According to the authors, the black carbon in the atmosphere, which rapidly circled the globe, likely combined with dust and sulfate aerosols to darken the planet and initiate an impact winter and a mass extinction event. — P.G.
Power of variational quantum algorithms
Variational quantum algorithms aim to solve hard computing problems by combining quantum resources with classical optimization methods. Although such algorithms have shown early promise with simple circuits, little is known about how they perform as the number of qubits and system complexity increase. Using an analog trapped-ion quantum simulator, Guido Pagano et al. (pp. 25396–25401) implemented a Quantum Approximate Optimization Algorithm (QAOA)—a hybrid quantum-classical variational quantum algorithm used for combinatorial optimization problems—to approximate quantum and classical solutions to an established hard problem: the ground-state energy of the Ising model with long-range interactions. The authors benchmarked the algorithm for different system sizes up to 40 qubits and report that its performance does not significantly degrade as the number of qubits increases. Additionally, the authors performed a comprehensive error analysis of the system that could help broaden the applications of QAOA. In a related article, Daiwei Zhu et al. (pp. 25402–25406) used an ion trap quantum computer to simulate two nontrivial, thermal quantum states of the transverse-field Ising model, a quantum version of the classical Ising model. Using a custom hybrid quantum-classical optimization loop inspired by the QAOA, the authors prepared a thermofield double state of the transverse-field Ising model—an entanglement structure closely linked with black holes—for a range of temperatures and the quantum critical state of the zero-temperature model. The authors note that the successful generation of these states on a quantum computer could aid studies of intriguing physical entities, such as teleportation protocols derived from a better understanding of black holes. Together, the findings suggest that combined quantum-classical variational algorithms might serve as a near-term alternative to fully realized quantum computing. — T.J.
Reference atlas of small noncoding RNAs in mouse tissues
Small noncoding RNAs (ncRNAs) are endogenously expressed transcripts that play vital roles in mediating essential cellular processes and regulating gene expression, but their tissue- and sex-specific expression patterns remain unclear. Alina Isakova et al. (pp. 25634–25645) used deep sequencing to systematically profile the expression of five ncRNA classes—microRNAs (miRNAs), small nucleolar RNAs (snoRNA), small nuclear RNAs (snRNAs), small Cajal body-specific RNAs (scaRNAs), and tRNA-derived small RNAs (tRFs)—across 11 different tissues in the C57BL/6J strain of mice. Using 14 biological replicates from adult mice of both sexes, the authors discovered many new ncRNA molecules and showed that about 30% of them were tissue-specific, with some also being sexually dimorphic. Some miRNAs were globally sexually dimorphic, whereas most were sex-biased only within a specific tissue. Each healthy mammalian tissue carried a unique ncRNA signature, with the brain containing the largest number of unique mammalian ncRNA transcripts. Integrating ncRNA measurements with single-cell chromatin accessibility profiles enabled the authors to map the expression of brain-specific ncRNA to their cell types of origin. The study provides broad characterization of small ncRNAs in mouse tissues, and the authors suggest that it could serve as a valuable resource for identifying ncRNA functions in health and disease. — S.R.
CRISPR-based malaria test
Among the barriers to malaria eradication are asymptomatic carriers who serve as parasite reservoirs and a lack of highly sensitive diagnostic methods suitable for use in resource-limited settings. Sensitive diagnostic methods are also needed for species of malaria parasites other than Plasmodium falciparum. Rose Lee et al. (pp. 25722–25731) developed a CRISPR-based diagnostic method to detect four species of the malarial parasite Plasmodium. The test, which uses a nucleic acid detection platform called SHERLOCK, begins with a 10-minute parasite extraction step, followed by a 60-minute species-specific detection process with readout by fluorescence or on a lateral flow strip. The authors report that the process is optimized for field conditions and resource-limited settings, with a cost of around $0.61 per test. The reaction materials are freeze-dried into a pellet that can be rehydrated, without the need for refrigeration. Additionally, the authors note that the P. falciparum test is capable of detecting below two parasites per microliter of blood—a threshold smaller than the World Health Organization’s recommended limit of detection for molecular testing. According to the authors, the test enables rapid, low-cost, sensitive diagnosis of symptomatic and asymptomatic malaria carriers, particularly carriers of nonfalciparum parasite species. — P.G.