Ecosystem impacts of megadroughts
Drifting sand in semiarid eastern Australia.
As the planet continues to warm, the magnitude of drought is likely to increase. However, the effects of megadroughts on animals, plants, and ecosystems are unclear. Robert Godfree et al. (pp. 15580–15589) developed a reconstruction of a severe, continent-wide megadrought interval that occurred in Australia between 1891 and 1903, known as the Australian Federation Drought period (FDP). The reconstruction included 541 biotic impact records with geocoded data from a broad range of flora and fauna and 1,748 drought impact records extracted from more than 35,000 contemporary newspaper articles and historiographic sources. Ecosystem impacts occurred most frequently during exceptionally dry conditions and were mostly concentrated in arid, semiarid, and dry subtropical parts of Australia. In semiarid areas, severe drought combined with livestock and rabbit overgrazing resulted in the mass mortality of shrubs and grasses. During the FDP, more than 60 bird, fish, mammal, reptile, and plant genera experienced severe stress and mortality over at least 36% of the Australian continent. The presence of hyperabundant herbivores increased ecosystem sensitivity to permanent degradation. The results suggest a bottom-up, ecosystem-wide mortality pattern mostly driven by record rainfall deficiencies, which put ecosystems at high risk of collapse, according to the authors. — M.S.
Comparative advantage and gender gap in reading and math
Women continue to be underrepresented in math-related fields. Image courtesy of Pixabay/777546.
Women remain underrepresented in math-related fields. However, students’ abilities do not explain gender differences in educational and career choices. Using individual-level data from 300,000 15-year-old students in 64 countries from the 2012 Programme for International Student Assessment, Thomas Breda and Clotilde Napp (pp. 15435–15440) found that female students who are proficient in math are more likely to be even more proficient in reading than male colleagues. Two-thirds of boys but only 30% of girls are more proficient in math than in reading. This gender gap in comparative advantage for math over reading may explain up to 80% of the gender gap in intentions to pursue math studies and careers, and may also explain the gender gaps in attitudes toward math at the age of 15. The findings suggest that the comparative advantage in math over reading at the time students make educational choices, which is likely to be determined by earlier socialization processes, plays a key role in women’s underrepresentation in math-intensive fields, according to the authors. — M.S.
Motor proteins and microenvironment influence brain tumor development
Schematic illustration of brain cancer cell. Image courtesy of iStock/Christoph Burgstedt.
Glioblastoma multiforme (GBM) is a deadly brain cancer that can blaze through the brain using multiple signaling pathways that fuel cell invasion. Therapeutic efforts to target individual pathways often fail due to the signaling redundancy. Pharmacologically blocking motor proteins of the nonmuscle myosin II (NMII) family, which is implicated in cell motility, curbs GBM invasion in vitro, despite simultaneous activation of signaling mechanisms promoting cell migration. Hannah Picariello, Rajappa Kenchappa, et al. (pp. 15550–15559) tested whether blocking NMII has similar effects in vivo. Genetic knockouts of both NMIIA and NMIIB, major types of the motor proteins, in a GBM mouse model reduced tumor formation and growth and prolonged survival. However, simultaneously targeting both protein types using drugs may prove too toxic, prompting the authors to target only NMIIA. Though tumor invasion was impaired in mice lacking NMIIA, the mice surprisingly exhibited increased tumor growth, driven by increased signaling mediated by ERK1/2 and NF-κB. The finding suggests that NMIIA suppresses tumors by tamping down ERK1/2 and NF-κB signaling. However, the effects of NMIIA loss on GBM growth depended on the mechanical properties of the tumor microenvironment. Using in vitro cell proliferation and invasion assays, the authors found that loss of NMIIA triggers ERK1/2 signaling on soft surfaces and NF-κB signaling on stiff surfaces. The latter finding comports with previous reports that enhanced stiffness of the extracellular matrix increases GBM aggressiveness. Hence, to be effective, GBM therapies must block both tumor proliferation and invasion, according to the authors. — P.N.
DNA analysis of Gibraltar Neanderthals
The remains of 2 Neanderthals from Gibraltar were excavated at Forbes’ Quarry in 1848 and Devil’s Tower in 1926. To investigate DNA preservation in the Neanderthal remains, Lukas Bokelmann et al. (pp. 15610–15615) analyzed 20 mg of petrous bone powder from the Forbes’ Quarry specimen and 36 mg of powder from the Devil’s Tower specimen. By looking for evidence of uracils in the DNA sequences, the authors determined that some highly deaminated ancient DNA molecules were present in both Neanderthal specimens; uracil typically results from damage caused by deamination of the DNA base cytosine in ancient DNA. However, most sequences were not from genuine Neanderthal DNA, but resulted from contemporary human DNA contamination, showing that the specimens’ DNA has not been well preserved. Therefore, the authors used a DNA preparation method that reduces modern contamination prior to sequencing to isolate the Neanderthal DNA component. The authors determined that the Devil’s Tower individual was male and the Forbes’ Quarry individual was female. The latter was genetically more similar to 60,000- to 120,000-year-old Neanderthal specimens in Europe and western Asia than to younger Neanderthal remains from Spain. The results suggest that it is possible to analyze ancient DNA in highly contaminated specimens, according to the authors. — M.S.