Commensal rats record shifts in Polynesian resources
View of Tikopia Island with its crater lake from the peak of Mt Reani.
Although little direct archaeological evidence exists to quantify the impacts of human colonization on local ecosystems, commensal animals, which accompany human habitation but are not domesticated, can preserve a record of ecosystem change in the isotopic composition of their remains. Jillian Swift et al. (pp. 6392–6397) analyzed isotope trends in Pacific rats dating between 800 BC and AD 1800 from three Polynesian island systems, covering the period of colonization. The authors report that nitrogen-15 isotope values declined over time in all three systems. The declines may reflect shifts in food sources for both humans and rats that are supported by other evidence, as humans transitioned from slash-and-burn agriculture to agroforestry and from offshore fishing to nearshore and terrestrial food sources. Other shifts include the loss of seabirds from rat diet and loss of seabird guano inputs to terrestrial systems, which may be due to extirpation or extinction. One island did not show a similar decline in nitrogen-15, and evidence suggests that constant human occupation at this site provided rats high-quality diets through continued access to marine foods rich in nitrogen-15. According to the authors, the results suggest that human colonization reshaped nutrient flows and that commensal animal isotopes can document human impacts on natural ecosystems. — P.G.
Protein synthesis and memory formation
Protein synthesis triggered by neural activity is required for memory formation in the brain. However, the effects of neural activity-induced synthesis of specific proteins on memory formation, as well as the precise window of protein synthesis crucial for memory formation, remain unclear. Using a rodent behavioral experiment in which paired exposure to a fearful context and electric foot shock were temporally separated, Kendrick Jones et al. (pp. E5805–E5814) found that elevated synthesis of the protein neurogranin (Ng) in the hippocampus is required for the formation of contextual memory; Ng is found in the dendrites and cell bodies of neurons and implicated in cognitive function and schizophrenia. Administration of anisomycin, which blocks fresh protein synthesis, 30 minutes or immediately before exposure of rodents to the fearful context prevented the formation of contextual memory, whereas anisomycin injection immediately or shortly after context exposure did not affect contextual memory. Neural activity-driven synthesis of Ng in the synaptic compartment was in turn dependent on the binding of the fragile-X mental retardation protein (FMRP) to Ng messenger RNA. According to the authors, exposure to novel contexts might trigger neural activity-induced synthesis of Ng in the hippocampus through an FMRP-dependent process and enable the encoding of new contextual memories. — P.N.
Enhanced directed evolution predicts antibiotic resistance
Predicting which new antimicrobial drugs are likely to trigger resistance remains a formidable challenge. Ákos Nyerges et al. (pp. E5726–E5735) present a method of directed evolution that can be applied across a range of bacterial species to quickly and accurately assess the mechanisms of resistance emergence. Built on multiplex automated genome engineering, an established technique to accelerate evolution, the authors’ approach can achieve up to 1 million-fold higher mutation rates than the wild type along multiple predefined genetic loci and without off-target modifications. The authors demonstrate that the technique, dubbed DIvERGE, can identify known resistance mutations to the antibiotics trimethoprim and ciprofloxacin within days and reveal previously unreported resistance-conferring mutations to ciprofloxacin at novel sites. Further, the authors note that the newly identified resistance mechanisms need in vivo validation. According to the authors, DIvERGE can potentially improve the directed evolution of multiple genes and can serve as a research tool in evolutionary biology. — T.J.
Characteristics of Earth’s early crust
A study explores Earth’s early crust. Image courtesy of NASA.
To uncover the origins of life and the continental crust on Earth, researchers must decipher the nature of the planet’s crust during the Hadean Eon, which ended 4 billion years ago. Previous studies of the Hadean crust have suggested a composition rich in iron, similar to the current oceanic crust, whereas more recent studies point to compositions rich in silica and potassium, similar to the current continental crust. However, researchers have suggested that the existence of a high-silica crust may be an artifact of contamination. To resolve the composition of the early crust, Patrick Boehnke et al. (pp. 6353–6356) examined the ratio of strontium isotopes in crystals of apatite preserved within Hadean-age rocks from Canada. The authors report that the ratio of strontium-87 to strontium-86 preserves the isotope ratio from the time of the crystal’s formation and is indicative of the amount of silica present in the rocks at the time. The results point to the likely existence of a silica-rich crust at around 4.2 billion years ago, suggesting that the crust had evolved its composition through several partial melts from iron-rich rocks. According to the authors, the composition also suggests that asteroid bombardment around 4.2 billion years ago was less significant than previously thought and that Earth, within 350 million years of solar system formation, may have been habitable. — P.G.
Health inequalities and the 2008 financial crisis
In the United States, rising mortality and morbidity among people with low education have led to increasing health inequalities since 2000. Johan Mackenbach et al. (pp. 6440–6445) assessed recent trends in health inequalities in European countries, as well as possible impacts of the 2008 financial crisis on health inequalities, based on mortality data from 1980 to 2014 for 17 countries and self-reported morbidity data from 2002 to 2014 for 350,000 survey respondents from 27 countries. The authors found that in western European countries, mortality declined steadily among people of high and low education levels throughout the period studied, with no interruption in this trend during the financial crisis. In eastern European countries, mortality among people of low education levels began to decline in recent years after having increased in previous decades, while a decline in less-than-good self-assessed health among men with low education accelerated. In the countries most severely hit by the financial crisis, declines in self-assessed health slowed following the crisis, but did so equally for people of low and high education levels. Crisis-related economic variables, such as declining national income and rising unemployment, were not associated with widening health inequalities. The results suggest that European countries avoided short-term aggravation of health inequalities from the financial crisis, according to the authors. — B.D.
History of lead pollution in the Balkans
A 1-m-long sediment drive from the lower part of the Crveni Potok sequence.
The metal-rich Balkan region of southeastern Europe contains some of the earliest archaeological evidence of complex mining and metallurgy on Earth. However, because of the discontinuous archaeological record from the Balkans, the scale and long-term environmental impact of metal resource exploitation in this region are unclear. Jack Longman et al. (pp. E5661–E5668) report a continuous, high-resolution record of past anthropogenic lead pollution in the Balkans based on geochemical data from a peat bog in Serbia, providing insight into the history of metal resource exploitation in the region. The earliest evidence of anthropogenic lead in this record occurred at the beginning of the Bronze Age, approximately 3600 BCE, centuries earlier than in previous records. Another notable feature of the record is a steady increase in anthropogenic lead from the beginning of the Iron Age, approximately 600 BCE, until the 17th century CE. This finding contrasts with records from western Europe, in which lead pollution levels peaked during the Roman period before declining. According to the authors, the record indicates a history of continuous mineral resource exploitation in the Balkans throughout the Roman, Byzantine, and medieval periods, suggesting that the Balkans played a key role in European mining, metallurgy, and associated environmental impacts. — B.D.