MICROBIOLOGY
Pacific oysters.
Nidovirus and mass mortality in Pacific oysters
Pacific oysters (Crassostrea [Magallana] gigas), a widely farmed shellfish species, have increasingly experienced mass-mortality events, often driven by unknown causes. Kevin Zhong et al. documented and characterized a previously unknown nidovirus, Pacific Oyster Nidovirus 1 (PONV1), in dead and dying Pacific oysters during a mass-mortality event in British Columbia in 2020. The authors identified PONV1 based on metatranscriptomic analyses of adult Pacific oysters at two affected farms and wild oysters with signs of disease. PONV1, a nidovirus that replicates in bivalves, possesses one of the largest reported genomes for an RNA virus at 64,331 base pairs. Genomic and phylogenetic analyses identified protein domains within the genetic architecture of PONV1 that are not found in other nidoviruses. Based on analysis of published transcriptomes from 44 studies, the authors identified 15 additional nidoviruses closely related to PONV1 in Pacific oysters from three continents belonging to the tentative species Megarnavirus gigas, representing a proposed nidovirus family Megarnaviridae. According to the authors, the global distribution of M. gigas and PONV1’s link to mass mortality underscore the potential risks involved in routine translocations of Pacific oysters across wide geographic areas. — M.H.
ENVIRONMENTAL SCIENCES
Farmer applying biochar to a paddy field.
Food security and sustainability benefits of biochar
Application of biochar, a form of charcoal, to soil can improve crop yields and reduce greenhouse gas emissions, contributing to food security and helping combat climate change. The long-term sustainability of annual biochar application under different soil conditions is unclear. Jingrui Yang, Longlong Xia et al. reviewed 438 published studies on the effectiveness of biochar application across global croplands, including 29 long-term field experiments conducted over 4 to 12 years. The analysis suggested that long-term annual biochar application resulted in sustained improvements in crop yields by an average of 10.8% across a variety of soil properties, management practices, and climatic conditions. Long-term biochar application also reduced average methane emissions by 13.5% and average NO emissions by 21.4%, likely due to suppression of methanogenic microbe growth, immobilization of microbial nitrogen, and enhancement of denitrifying microbe activity. Long-term biochar application also increased soil organic carbon content by 52.5% on average. In contrast, the benefits of one-time biochar application diminished over time, likely due to gradual decomposition and erosion. According to the authors, periodic biochar application optimized to local conditions could help improve both agricultural productivity and environmental sustainability. — M.H.
EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES
Dinosaur teeth preserve atmospheric isotopes
Because air-breathing organisms incorporate a fraction of atmospheric oxygen into the water found in their tissues, analysis of oxygen isotopes in dinosaur tooth enamel may constrain the atmospheric oxygen isotopic composition of the Mesozoic Era, which is correlated with CO2 concentrations. Dingsu Feng et al. compared oxygen isotopes of bones and teeth from modern birds and reptiles with 22 dinosaur tooth enamel samples from the Cretaceous and Jurassic periods. The analysis focused on oxygen-17 isotopes, which are correlated not only with atmospheric CO2, but also with primary biomass productivity. Assuming that primary productivity during the Mesozoic Era was the same as present-day primary productivity, the analysis suggests that CO2 levels were around four times higher than pre-industrial levels in the late Jurassic period and around 2.5 times higher than pre-industrial levels in the late Cretaceous period, values that generally agree with paleoclimate reconstructions. However, if primary productivity fluctuated in the Mesozoic Era, the isotope values instead indicate a productivity rate between 20% and 120% higher than present-day productivity. According to the authors, the findings suggest that oxygen isotopes in fossil tooth enamel may serve as an additional proxy for uncovering past greenhouse gas and climate conditions. — P.G.
ASTRONOMY
Proposed class of habitable planets
As numerous exoplanets are discovered and characterized by advancing telescope technology, many are deemed uninhabitable because they are too warm for the presence of liquid water. However, water may not be the only liquid that can support life. Rachana Agrawal et al. explored the possibility that ionic liquids, which are liquid salts with negligible vapor pressure, may form and persist on planets that are too warm to support the existence of liquid water. Lab experiments showed that ionic liquids can form from a combination of sulfuric acid and nitrogen-containing organic molecules, both of which are components expected to be commonly found on a subset of planets. Because ionic liquids do not readily evaporate, even in a vacuum, they can persist in small pools or droplets and can exist on planets with even negligible atmospheres—if they are shielded from cosmic radiation by magnetic fields or rock features. Ionic liquids can dissolve enzymes and biomolecules and could thus serve as solvents for biological processes. According to the authors, pockets of such liquids may create conditions of habitability that do not require water or substantial atmospheres, expanding the definition of extraterrestrial environments that could host life. — P.G.
ECOLOGY
Aphrodite fritillary, a rapidly declining species. Image credit: Ronda Spink (Michigan Butterfly Network, Kalamazoo, MI).
Declining abundance across midwestern US butterfly communities
Widespread declines in butterflies have been documented, but it is unclear how such declines are distributed across species and groups, including common versus rare butterflies and butterflies that migrate as adults versus those that remain local to overwinter as eggs. Wendy Leuenberger et al. combined more than 4.3 million observations of 136 butterfly species from the past 32 years to characterize changes in butterfly biodiversity across the midwestern United States. The authors report that 59 of the 136 species have declined in abundance over the study period, with no species increasing in abundance. For every 10 species and 100 individuals present in a county in 1992, there are now only nine species and 60 individuals. Across groups, common species declined more rapidly than rare species; counties are becoming more even in abundance across butterfly species. Species that overwinter as eggs declined more than species that overwinter at other life stages. Widespread declines among butterflies are likely to have cascading effects across ecosystems because butterflies provide myriad ecosystem services, including pollination, herbivory, prey for other animals, and decomposition. According to the authors, the findings could aid butterfly conservation efforts and suggest the need to target all butterflies, rather than just flagship and rare species. — M.H.
The arms and heads of opossums (pictured here one day before birth) and other marsupials develop faster than their legs and back bodies. Image credit: Sergio Menchero Fernandez (Francis Crick Institute, London, United Kindgom).
In opossums, gene expression follows familiar rules but at a strange pace
Posted on August 8, 2025
Amy McDermott
Short-tailed opossums aren’t exactly cute when they’re born. After just a two-week gestation, the tiny, hairless, gooey pink babies crawl out of mom and up onto her stomach, where they latch onto a teat and stay for at least a month. Most marsupials have a similar early life, in which tiny fetus-like babies, after they’re born, immediately crawl to a pouch or nipple to finish development. Intriguingly, marsupials tend to be born with well-developed heads and arms, perhaps for crawling to the pouch, but much less developed hindlegs and posterior bodies.