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Highlights in PNAS
New for December 12, 2018
Ecology
A patch of the endangered monkey puzzle tree (Araucaria araucana)
on the Argentine Pampas.
Loss of small habitats threatens biodiversity
Many conservation and public policy efforts focus on protecting large, connected landscapes rather than isolated patches of vegetation. However, land clearing and degradation pose greater risks to small, isolated patches of habitat than large ones because small habitats are often considered to have lower conservation value. Brendan Wintle et al. report that isolated habitat patches less than 1,000 hectares in size have high conservation value and are crucial to the survival of terrestrial species unique to those patches. The authors analyzed the results of 31 conservation studies across 27 countries in Africa, Australia, Europe, and North America. Each study used species distribution maps and a software program that identifies land conservation value. Areas with high conservation value tended to be isolated habitat patches, less than 10 hectares in size, and embedded in agricultural or urban environments. Conservation value was generally lower in large and mostly intact habitats because those areas tended to harbor species that were common throughout the landscape. According to the authors, the study underscores the significance of protecting small habitat patches, which may host rare or threatened species. — M.S.
"Global synthesis of conservation studies reveals the importance of small habitat patches for biodiversity," by Brendan A. Wintle, et al.
Article
Ecology; Earth, Atmospheric, and Planetary Sciences
Artistic rendering of North American Pliocene fauna.
Image courtesy of Wikimedia Commons/Jay Matternes.
Past analogs of projected future climates
Climates from Earth’s deep past may provide analogs for possible near-future climates, but past and projected future climates have not been quantitatively compared. K. Burke, J. Williams, et al. compared mean summer and winter temperatures and precipitation projected for 2020–2280 CE to those from two historic and four prehistoric warm periods spanning the last 50 million years. The authors found that Mid-Pliocene climates, 3.3–3 million years ago, replaced historical precedents as the best analog for future climates after 2030 CE. Under a scenario in which greenhouse gas emissions stabilize by the mid-21st century, Earth’s projected climate stabilized at Pliocene-like conditions. Under an unmitigated emissions scenario, global climates began to resemble those of the Early Eocene, 50 million years ago, by 2150 CE. In the latter scenario, up to 9% of projected climates had no close analog among any of the past climates examined. Both Pliocene-like and Eocene-like climates emerged initially in the continental interiors and subsequently spread outward. Hence, the results suggest that unmitigated greenhouse gas emissions may result in the reversal of a 50-million-year cooling trend in two centuries, according to the authors. — B.D.
"Pliocene and Eocene provide best analogs for near-future climates," by K. D. Burke, J. W. Williams, et al.
Article
New for December 5, 2018
Earth, Atmospheric, and Planetary Sciences
Altimeter era sea-level trends.
Sea-level rise and climate variability
Satellite altimetry data have provided detailed and accurate data on sea-level rise since 1993. However, the extent to which observed changes in sea level reflect natural climate variations and long-term trends driven by external forcings, such as aerosols or greenhouse gas emissions, remains unclear. To address this question, John Fasullo and R. Steven Nerem analyzed two large ensembles of 30–40 climate simulations, with each ensemble based on a single climate model. The authors calculated the forced response (FR) due to external factors by averaging all of the simulations in an ensemble together, thereby canceling out the effects of internal variability. In both ensembles, spatial patterns of change during the altimeter era (1993–2018) in each of the individual simulations in the ensemble correlated significantly with those due to the FR, much more so than in a control ensemble of unforced simulations. In addition, the altimeter era FR was significantly correlated with that simulated for 2020–2045. The results suggest that a significant amount of the trends in sea level measured by altimetry is due to external forcing and that such trends are likely to persist over the coming decades, according to the authors. — B.D.
"Altimeter-era emergence of the patterns of forced sea-level rise in climate models and implications for the future," by John T. Fasullo and R. Steven Nerem
Article
Ecology
Bee collecting pollen. Image courtesy of Wikimedia Commons/Jon Sullivan.
Pesticides and honey bee mass mortality
Mass honey bee mortalities occurred in France in the 1990s following the introduction of two pesticides, imidacloprid and fipronil. The former compound was initially thought to be the causal agent, but laboratory studies combined with modeling simulations point to the latter being more likely involved in honey bee deaths. Philippa Holder et al. measured dose-dependent mortality rates for imidacloprid, fipronil, and two other widely used pesticides in bees from outdoor hives, and used the data to model colony-level effects in demographic simulations. The simulations predicted 4,000–9,000 more bee deaths than control conditions during the first week of fipronil exposure, leading to colony collapse within 2 or 3 weeks. None of the other pesticides resulted in mortality sufficient to cause colony collapse. The authors employed two assays, recommended by proposed international regulatory guidelines, for determining the ability of potentially toxic compounds to bioaccumulate. Fipronil exhibited signs of toxic bioaccumulation in both assays, whereas the other pesticides showed no signs of bioaccumulation in either assay. The authors found that toxic fipronil metabolites from a single meal persisted in honey bees for at least 6 days. The results implicate fipronil as a likely cause of the mass honey bee mortalities in France in the 1990s and demonstrate the value of the proposed bioassays for identifying harmful bioaccumulative substances, according to the authors. — B.D.
"Fipronil pesticide as a suspect in historical mass mortalities of honey bees," by Philippa J. Holder, Ainsley Jones, Charles R. Tyler, and James E. Cresswell
Article
Ecology; Sustainability Science
Artistic rendition of global conservation risk hotspots for land plant species.
Image courtesy of Abbie Zimmer (Ohio State University, Columbus, OH).
Machine-learning approach identifies plants at risk of extinction
Plant biodiversity supports food chain diversity, helps counter natural disasters, and contributes to ecosystem productivity. The International Union for Conservation of Nature Red List of threatened species contains only a small fraction of extant species on Earth, partly because species assessments are expensive and time-consuming. Tara Pelletier et al. developed a machine-learning approach to predict plant species at risk of extinction using open-source geographic, environmental, and morphological trait data for more than 150,000 land plant species. The authors identified variables predicting extinction risk, including geographic and bioclimatic traits, and calculated the probability of a species being designated “at risk” based on the traits. The authors report that a large number of previously unassessed land plant species are likely at risk of extinction and may need to be considered for inclusion in the Red List. Further, the approach can be used to identify species at the highest extinction risk and to pinpoint geographic regions with the greatest need for conservation efforts by pairing GPS coordinates with risk probabilities. According to the authors, the approach can be used to guide policies aimed at allocating resources for biodiversity conservation. — T.G.
"Predicting plant conservation priorities on a global scale," by Tara A. Pelletier, Bryan C. Carstens, David C. Tank, Jack Sullivan, and Anahí Espíndola
Article
Evolution
Inosine monophosphate, a possible component of primordial RNA.
Image courtesy of Wikimedia Commons/Jynto.
Primordial RNA and origins of life
RNA is believed to have played both genetic and catalytic roles early in the evolution of life, but the origins of RNA and its precursors remain uncertain. However, prebiotic synthesis of adenine and guanine, two of the canonical nucleobases that make up RNA, remains challenging. Seohyun Chris Kim et al. tested whether the 8-oxo-purines, which could plausibly be synthesized prebiotically, and inosine could replace adenine or guanine in a functional RNA molecule. Activated 8-oxo-purine nucleotides were incorporated into a growing RNA strand at a much slower rate than the canonical nucleotides. Once incorporated, the 8-oxo-purines significantly slowed the incorporation of the next nucleotide. The presence of 8-oxo-purines in the template strand resulted in high copying error rates compared with the canonical nucleotides. By contrast, activated inosine nucleotides were incorporated at rates comparable to those of canonical nucleotides and exhibited specificity for forming base pairs with cytosine comparable to that of guanine. Incorporation of inosine into the strand had a minimal impact on the rate of incorporation of subsequent nucleotides. The results suggest that inosine could have substituted for guanine in an early version of RNA-based life, according to the authors. — B.D.
"Inosine, but none of the 8-oxo-purines, is a plausible component of a primordial version of RNA," by Seohyun Chris Kim, Derek K. O’Flaherty, Lijun Zhou, Victor S. Lelyveld, and Jack W. Szostak
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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