Dental anomaly and body size variation in dogs
Shetland sheepdogs illustrate within-breed body size variation. Image credit: Nancy Ager (photographer).
Maxillary canine tooth mesioversion, or lance canine, is a dental anomaly in dogs in which a displaced upper canine tooth can cause painful occlusion, upper lip ulceration, and periodontal disease. The genetic basis of lance canine, which rarely afflicts breeds other than Shetland Sheepdogs, remains unclear. Sydney Abrams et al. (pp. 24929–24935) used a genome-wide association study and whole genome sequencing to uncover risk factors of lance canine in Shetland Sheepdogs, a small breed that stands 13–16 inches tall. The analysis yielded risk variants in two genes on chromosome 9: A single base insertion in GH1, which encodes a growth hormone implicated in human pituitary dwarfism, causes incomplete processing of GH1 RNA, and a single amino acid change in FTSJ3, which encodes an enzyme involved in RNA processing and cell proliferation, likely affects the enzyme’s activity. The variants were associated not only with lance canine but also body height and weight, and the authors found that dogs with lance canine were shorter and weighed less than control dogs. Notably, each copy of the FTSJ3 variant reduces size by around 1 inch and 5 pounds. Additional analysis in 1,049 dogs of 224 breeds revealed the variants’ presence in an array of toy breeds, including Chihuahuas, Miniature Pinschers, Pomeranians, Toy Poodles, and Yorkshire Terriers, but not in larger breeds. According to the authors, the study uncovers a genetic locus in dogs that influences body size and is tied to a dental anomaly. — P.N.
Antarctic ice shelf damage and instability
Thwaites Glacier. Image credit: NASA.
The Pine Island and Thwaites Glaciers, located in the Amundsen Sea Embayment of Antarctica, have undergone rapid acceleration, thinning, and grounding line retreat in recent decades, leading to enhanced instability. Projecting future changes in these glaciers that could have large consequences for sea level rise remains challenging. Stef Lhermitte et al. (pp. 24735–24741) used satellite imagery to document the growth of damage areas on the ice shelves of these glaciers from 1997 to 2019. The damage areas consist of highly crevassed areas and open fractures within the shelves’ shear zones, where the ice is thin and which experience high positive strain rates. This damage can precondition the ice shelves for further disintegration by compromising ice shelf integrity and because of feedbacks between damage, acceleration, and shearing. Ice sheet modeling that incorporates this damage identified damage feedback mechanisms as important drivers of ice shelf instability and grounding line retreat and, consequently, of future Antarctic contributions to sea level rise. According to the authors, the results emphasize the importance of incorporating damage processes in ice sheet models to improve sea level rise projections. — B.D.
Hydrothermal activity in hominin environments
Excavation of FLK West and the Gorge, archaeological sites where early evidence of Acheulean technology at Olduvai Gorge has been found.
The earliest known example of hominin tools associated with Acheulean technology in the Olduvai Gorge in Tanzania dates to 1.7 million years ago. At that time, East Africa, including the Olduvai Gorge, was undergoing a drying trend that shaped the environment in which hominins evolved. Ainara Sistiaga et al. (pp. 24720–24728) analyzed lipid biomarkers and isotope signals to reconstruct the paleoenvironment present at the beginning of Acheulean technology. Fossil molecules recovered from Acheulean-age sedimentary layers included lipids interpreted as biomarkers for thermophilic sulfate-reducing bacteria and other species typically found at hydrothermal features such as at Yellowstone National Park. Evidence of organic matter with different maturities suggests that the potential extrusion of fluids could have resulted in the formation of hydrothermal petroleum. The dynamic landscape, shaped by tectonics and hydrothermal activity, likely hosted significant biodiversity, which could have offered hominins the opportunity to hunt herbivores attracted to the region. Further, hydrothermal streams or pools may have reached temperatures around 80–90 °C, making it possible for hominins to cook roots and tubers and increase the availability of nutrients before the discovery of fire. According to the authors, the biodiversity and potential culinary use of hydrothermal streams and pools may have conferred evolutionary advantages to the hominins of Olduvai Gorge. — P.G.
City-dwelling mosquito and malaria risk in Africa
Africa has the highest global incidence of malaria, which is spread by mosquitoes. Since 2012, increasingly severe outbreaks of malaria thought to be caused by Anopheles stephensi, an Asian mosquito species that thrives in urban settings, have been reported in Djibouti City in the Horn of Africa, and the species has been found recently in Ethiopia and Sudan. To predict the spread of An. stephensi in Africa, Marianne Sinka et al. (pp. 24900–24908) combined location data for An. stephensi across its full geographic range with spatial models that identify the environmental conditions characterizing the species’ preferred habitat. The authors generated maps predicting the possible locations across Africa where An. stephensi could establish if allowed to spread unchecked. The results showed that 44 out of 68 African cities are predicted to be highly suitable locations for this species. As a result, approximately 126 million additional people could be at a heightened risk of malaria if An. stephensi continues its invasion across the continent. According to the authors, the findings highlight the importance of adhering to the World Health Organization recommendations for An. stephensi surveillance efforts and targeted responses to prevent additional malaria-related illness and deaths. — J.W.
Rainfall and rhizosphere function in old-growth forests
During times of intense drought, trees exhibit reductions in belowground carbon demand due to the degraded function of the rhizosphere, which consists of roots and root-associated microbiomes. However, many details about the reallocation of resources remain unclear, including how trees partition carbon when water is limited and how they revert once drought has lifted. Jobin Joseph, Decai Gao, et al. (pp. 24885–24892) used 13CO2 pulse labeling to assess rhizosphere metabolic activity in trees and monitor assimilate fluxes and storage in aboveground and belowground carbon pools during and after drought. The authors tracked 10 mature trees in a naturally drought-exposed 100-year-old Scots pine forest and found that drought reduced transport of new assimilates to belowground reservoirs by around 53%, but brief periods of rainfall substantially increased the rate of carbon transport into the soil. In addition, the switch to a new allocation regime was consistent with a tipping point in soil microbe respiratory activity at around 15% soil water content. The study reveals that even small increases in soil moisture can rapidly restore rhizosphere function and offers insight into how projected increases in severe weather, such as frequent drought, might affect Earth’s forests, according to the authors. — T.J.
Childhood maltreatment and mitochondrial changes
Childhood maltreatment, such as neglect and abuse, can have long-lasting effects on mental and physical health. Through unclear mechanisms, the descendants of mothers who experienced childhood maltreatment are at increased risk for a variety of physical and mental health problems, including asthma, allergies, autism, and attention-deficit hyperactivity disorder. Anja Gumpp et al. (pp. 24778–24784) explored the potential role of mitochondria, which are intracellular energy-producing organelles that are primarily inherited from mothers and key components of the stress response in humans. In a sample of 102 healthy mother–newborn dyads, the authors examined the relationship between maternal childhood maltreatment, which was assessed with a questionnaire, and the respiration and density of mitochondria in the mothers’ blood cells and in the umbilical cord blood cells of their newborns. Childhood maltreatment was associated with increased mitochondrial density and respiration in mothers, but not in their newborns. Although larger scale studies are needed to confirm the results, the study suggests that the intergenerational effects of childhood maltreatment may not involve the transmission of mitochondrial alterations from mothers to offspring. However, the effects need to be explored in mothers with a high burden of childhood maltreatment, according to the authors. — J.W.
Multiple signatures of major depressive disorder
Depression is a common, debilitating disorder that affects multiple levels of brain biology. However, most studies on the neurobiological basis of depression consider only one or two such levels at a time. Kevin Anderson et al. (pp. 25138–25149) integrated multiple analyses to better understand the biological basis of depression. Using three imaging datasets including a total of 23,723 participants, the authors found that individuals with a history of depression or negative mood exhibited thinner cortex, which is the outermost layer of neural tissue in the brain; lower correlated signal among different cortical regions; and increased resting-state amplitude, which is a property of brain fluctuations that occur when no task is being performed. These effects were observed in consistent brain regions across the datasets. Postmortem cortical samples from a different group of 83 patients with depression revealed the most pronounced alteration in depression-related gene expression in two cell types: somatostatin interneurons and astrocytes. Genome-wide association study data also indicated that depression risk is associated with interneuron-specific genes. Overall, the study suggests that gene expression in somatostatin interneurons and astrocytes in vulnerable brain regions may play a role in depression and negative mood. According to the authors, integrative neuroscience approaches could lead to novel therapeutic strategies for depression. — J.W.
Metallizing diamond
Strain and bandgap mapping of a bent diamond nanoneedle.
Recent studies have shown that nanoscale diamond needles can significantly deform and return to their original states at room temperature. These demonstrations allow the use of strain engineering to exploit or alter the unique material properties of diamond. Zhe Shi, Ming Dao, et al. (pp. 24634–24639) report that the application of mechanical strain alone can “metallize” diamond, closing the large bandgap that makes diamond an excellent insulator and imbuing the material with metal-like electronic properties. The authors performed computer simulations of reversible deformation and used the results as a training set for machine learning algorithms, which home in on optimal material properties and loading conditions for diamond across various geometries. The authors found that even simple bending of certain monocrystalline diamond nanoneedles can effectively metallize diamond at strains below levels that would fracture or destabilize the material’s atomic structure or trigger a phase transition to graphite. The findings could enable strategies to customize the properties of diamond for an array of unexplored electronics and quantum sensing applications, according to the authors. — T.J.