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Highlights in PNAS
New for May 20, 2020
Earth, Atmospheric, and Planetary Sciences
Hurricanes Katia (Left), Irma (Center), and Jose (Right) over Mexico
and the Caribbean on September 8, 2017. Image credit:
Wikimedia Commons/NOAA View Global Data Explorer.
Trends in tropical cyclone intensity
Theory and models suggest that tropical cyclone (TC) intensity tends to increase with global mean surface temperatures. However, such a trend is difficult to detect in observations because of spatial and temporal heterogeneities in the instrumental record. To increase the confidence in the trend extracted from observations, James Kossin et al. extended an existing globally homogenized record of satellite imagery to encompass the period 1979–2017. The record had previously covered the years 1982–2009 and exhibited increasing trends in global TC intensity, but the trends were not statistically significant. The authors found that the probability of a hurricane having wind speeds of at least 100 knots increased by approximately 15% between the early and latter halves of the 39-year record. This finding corresponds to a statistically significant rate of increase of approximately 8% per decade. A time series of the proportion of all hurricanes exceeding 100 knots exhibited a similar increasing trend of approximately 6% per decade. The results are consistent with the predictions of physical theory and numerical simulations and increase confidence in the view that TCs have become stronger under global warming, according to the authors. — B.D.
"Global increase in major tropical cyclone exceedance probability over the past four decades," by James P. Kossin, et al.
Article
Ecology
Tethered apple fly (Rhagoletis pomonella) approaching a
tree-like virtual object in a multimodal virtual reality arena.
Flying insects use cues to navigate toward virtual objects
Flying insects are remarkable for their ability to rapidly locate objects such as food and mates while exploring a complex 3D world. However, how insects accomplish this computationally intensive feat during flight, especially over large spatial scales, is unclear. Pavan Kaushik et al. used virtual reality to examine the behavior of tethered flying insects, including apple flies, mosquitoes, hoverflies, and crane flies. The virtual reality arena consisted of complex 3D visual scenery with grass, sky, trees, and flowers, as well as odors and wind tunnel-like airflow fields. All four Dipteran species located and approached flowers or trees, which are preferred sites for mating, feeding, or egg-laying in the real world. In addition, apple flies were more likely to approach close trees than faraway trees, suggesting that the flies use depth cues such as perspective and motion parallax to determine virtual object distance. Moreover, apple flies combined directional airflow and odor information to locate and move toward virtual fruit-blend odor plumes. Taken together, the findings demonstrate that flying insects integrate multiple types of sensory cues to locate and navigate toward virtual objects in a complex 3D landscape. According to the authors, the findings could be used to optimize strategies for pest control, crop pollination, and disease vector management. — J.W.
"Characterizing long-range search behavior in Diptera using complex 3D virtual environments," by Pavan Kumar Kaushik, et al.
Article
Pharmacology
Species-rich rainforests of Mount Halimun Salak National Park, Java, Indonesia.
Phylogenetically guided drug discovery
Multidrug-resistant bacteria have emerged as a major global public health threat resulting from high antibiotic use in healthcare and livestock, prompting the need to identify new antibiotics. Laura Holzmeyer, Anne-Kathrin Hartig, Jan Schnitzler, et al. developed a method to search for potential antiinfective lead compounds in plants by integrating phylogenetic, spatial, and bioactivity data. As a test case, the authors examined more than 16,000 secondary metabolites found in more than 7,500 seed plant species on the Indonesian island of Java. The authors identified 26 plant clades in which antiinfective activities were overrepresented and therefore have a high probability of yielding bioactive compounds. The authors also identified 24 clades in which such activities were underrepresented. The clades have an overall low probability of yielding antiinfectives, but any antiinfective found has a high probability of being a novel type of antiinfective. Comparison of the geographic distributions of plant species and plant metabolites revealed a strong correlation between species diversity and metabolite diversity, reinforcing the importance of conserving biodiversity hotspots. The approach could help guide the search for novel antiinfective compounds by identifying promising taxa and geographic areas, according to the authors. — B.D.
"Evaluation of plant sources for antiinfective lead compound discovery by correlating phylogenetic, spatial, and bioactivity data," by Laura Holzmeyer, Anne-Kathrin Hartig, Jan Schnitzler, et al.
Article
Environmental Sciences; Sustainability Science
In the current climate, MATs above 29 °C are restricted to small,
dark areas in the Sahara region. In 2070, such conditions are
projected throughout the shaded area in the worst-case scenario.
Background colors represent current MATs.
Climate niche history of humans
As Earth’s climate continues to warm, some regions may become unsuitable for human life while conditions in other regions improve. Chi Xu et al. examined data from several sources that included global temperature, human population, and land-use estimates dating from the mid-Holocene, 6,000 years ago, to 2015 CE. The authors also estimated future human populations and global climate conditions by 2070 CE to determine where optimal climate conditions may occur. Humans, crops, and livestock are currently concentrated in a narrow subset of suitable climate space, which exhibits a mean annual temperature (MAT) of approximately 11–15 °C. The authors report that such conditions suitable for human life have remained largely the same since the mid-Holocene. The authors predicted that by 2070 approximately 1–3 billion people are likely to live under climate conditions that are warmer than conditions deemed suitable for human life to flourish. The findings suggest the need to enhance human development in areas where adaption to climate change is low. Furthermore, future migration from regions undergoing degradation from climate change to regions with ideal climates may be necessary, according to the authors. — M.S.
"Future of the human climate niche," by Chi Xu, et al.
Article
Some of the highlights have previously appeared on the PNAS media tipsheet. The articles in PNAS report original research by independent authors and do not necessarily represent the view of the National Academy of Sciences.
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