Lagging adaptation in banked seeds
Organisms unable to rapidly adapt to climate change may decline and disappear from their previous habitats. Restoring populations of plants from seed banks may be unsuccessful if the seeds’ preferred climate does not match the target region’s new climate. Immigrant plants of the same species from historically warmer climates, however, may be able to thrive. Amity Wilczek et al. (pp. 7906–7913) planted banked seeds of Arabidopsis thaliana in four locations across the species’ native European range. Although seeds originating from sites near the planting locations performed well at each site, varieties originating from climates historically warmer than the planting sites’ displayed greater fitness than the native varieties, especially at the northernmost planting site in Finland. The authors also found that the season of germination affected fitness of immigrant plants from warmer climates at a site in the United Kingdom, and that populations with summer germination may be better suited to warm future climates than populations with other germination seasons. The results suggest that banked seeds may be subject to adaptation lag within a few decades, complicating plant conservation efforts using banked seed populations, according to the authors. — P.G.
Wireless powering of small implantable medical devices
Implantable electrostimulator without batteries. Image courtesy of Austin Yee (photographer).
Engineering advances have enabled the miniaturization of electronic medical implants, but methods for powering the implants have not kept pace. John Ho et al. (pp. 7974–7979) investigated an alternative to conventional near-field wireless power transfer, which has a range limited by the size of the implant, by employing a technique called midfield powering, which can theoretically reach small but deeply implanted medical electronics. The authors designed a patterned, electromagnetic metal plate that, when held near porcine tissue, delivered up to 2,000 µW of power through 5 cm of tissue to reach the heart or brain. Conventional pacemakers require 8 µW of power, a fraction of the power generated by the electromagnetic plate. An experiment with a rabbit demonstrated the plate’s ability to power an electrostimulator implanted 4.5 cm deep on the surface of the heart, enabling regulation of the rabbit’s cardiac rhythm. The plate transmitted power at a level below the threshold for human safety, and patterning on the plate’s surface enabled the electromagnetic field to be focused on a small area around the microimplant. According to the authors, the results demonstrate that a midfield wireless device may safely power or recharge microimplants through different tissue types. — J.P.J.
Phosphorus cycling by Sargasso Sea phytoplankton
In areas of the ocean where the essential nutrient phosphorus is abundant, phytoplankton store excess phosphorus in reserves of polyphosphate molecules. In low-phosphorus areas of the ocean, however, phytoplankton can alter their biochemistry to decrease their need for phosphorus. Patrick Martin et al. (pp. 8089–8094) studied phytoplankton in the phosphorus-poor Sargasso Sea in the North Atlantic. Despite low concentrations of dissolved phosphorus in the ocean water, the authors found that the phytoplankton were enriched in polyphosphate, a molecule previously thought to be produced only in areas of phosphorus abundance. The phytoplankton displayed biochemical signs of phosphorus stress, such as substitutions of sulfur for phosphorus in lipid synthesis, suggesting that polyphosphate may also be a key response to phosphorus scarcity. But the authors found that polyphosphate molecules were more readily released into the water from sinking organic matter than bulk phosphorus, resulting in recycling of bioavailable phosphorus into shallow waters. The results imply that efficient cycling of polyphosphate may form a feedback loop that contributes bioavailable phosphorus to support phytoplankton production, according to the authors. — P.G.
High-throughput sequencing of a mixed environmental sample
Malaise trap for mass capture of flying insects.
Arthropod identification methods are typically based on morphology or involve DNA sequencing of individual specimens, but these methods can be expensive and time-consuming. Joel Gibson et al. (pp. 8007–8012) used next-generation sequencing (NGS) technologies to simultaneously detect multiple individual species within a sample of mixed arthropods from northwestern Costa Rica. The authors mass captured and homogenized 1,066 arthropod specimens, and sequenced the mixed sample using an NGS platform that employed 11 sets of PCR primers designed through comparative analysis of more than 128,000 arthropod DNA bar code sequences, specifically of the mitochondrial cytochrome c oxidase I gene. Traditional morphological and single specimen sequencing methods used to identify the arthropod specimens helped confirm that the NGS method accurately detected the presence of 91% of all individually sequenced arthropod specimens in the sample and 30 additional arthropod species that could not be morphologically recognized. Further, bacteria and protozoa in the arthropod sample were detected using NGS of the ribosomal RNA genes. According to the authors, the results suggest that the NGS methods can simultaneously detect arthropod, bacterial, and protozoan species within a mixed environmental sample, reducing the time and cost required by morphological and single specimen sequencing methods. — J.P.J.
Reconstructing the origin of the 1918 pandemic flu virus
The flu pandemic of 1918–1920 killed an estimated 50 million people, but the pandemic’s origin and epidemiology, and the reasons for its unusual severity among young adults, are still unclear. Michael Worobey et al. (pp. 8107–8112) used a molecular clock approach to reconstruct the origins of the 1918 pandemic influenza A virus (IAV), a swine H1N1 influenza virus, and the postpandemic seasonal H1N1 lineage, and inferred that the pandemic virus likely arose shortly before 1918 due to reassortment between a human H1 virus and an avian virus. IAV typically kills infants and the elderly, but the pandemic virus caused extensive mortality in 20–40-year-old adults. The authors suggest that this finding is likely because many young adults born from approximately 1880–1900 were exposed during childhood to an antigenically distinct H3N8 virus, and thus may have lacked immunological protection to the pandemic virus. People born earlier or later than approximately 1880–1900 would have had some partial protection against the 1918 H1N1 virus due to childhood exposure to N1 and/or H1-related antigens. Childhood exposure of different age groups to different influenza virus variants may have been a key factor underlying the age-specific patterns of fatality not only in 1918 but also during other pandemics and seasonal influenza epidemics, the authors suggest. — S.R.
L1 retrotransposons and human genetic variation
LINE-1 (L1), a class of retrotransposons that accounts for nearly 20% of the human genome, is considered a major source of genetic variation among individuals. Previous studies have found that these mobile elements can disrupt genes, contributing to diseases such as cancer, and regulate the expression of neighboring genes by altering the transcriptional architecture. Alexandre Kuhn et al. (pp. 8131–8136) analyzed L1 insertions in genome sequence data pertaining to 20 people of Asian origin and from the 1000 Genomes Project, a public catalog of human genetic variants found in at least 1% of any population. The authors report that most L1 insertions could be tagged by genetic variations called single nucleotide polymorphisms (SNPs), suggesting that the L1 retrotransposons were in high linkage disequilibrium with their surrounding genomic regions. High linkage disequilibrium indicates that the L1 retrotransposons are nonrandomly associated with neighboring SNPs, which could therefore serve as proxies for L1 in tests of phenotypic effects. Further, the authors found signs of recent positive selection around several L1 insertions within different human populations. According to the authors, L1 insertions might indeed trigger significant phenotypic differences that can serve as substrates for natural selection. — P.N.