Diet and gut microbiome of African megafauna
Reticulated giraffe plucks a Hibiscus meyeri plant from within a clump of the shrub Croton dichogamus at the Mpala Research Centre in Kenya.
Diet and gut microbiome composition are important for mammalian health, but their fluctuation in response to environmental changes is unclear. Tyler Kartzinel et al. (pp. 23588–23593) collected and analyzed fecal samples from 33 large herbivore species from Laikipia, Kenya, over 5 1-month sampling periods between 2013 and 2016. To assess seasonal variation in diet and microbiome composition, the authors sequenced bacterial and plant DNA. Diet composition was correlated with microbiome composition across most species. Phylogenetic relatedness predicted microbiome composition and was correlated with diet composition, whereas dietary diversity did not predict the microbiome diversity of any species, except kudu. Diet and microbiomes also changed seasonally as rainfall waxed and waned. Overall, seasonal shifts in diet composition predicted 25% of seasonal turnover in microbiome composition. Species such as elephants exhibited little variability in either diet or microbiome, whereas species such as camels exhibited significant differences in both. Along this spectrum, domesticated species exhibited greater diet–microbiome turnover than wild species. Further, diets were often more diverse in the dry season and dominated by relatively few plant taxa in the wet season. The results suggest that understanding diet–microbiome links could help explain food-web structures within communities and ecological differences between livestock and wildlife, according to the authors. — M.S.
Pathology of age-related macular degeneration
Age-related macular degeneration (AMD) is often characterized by the accumulation of cellular and extracellular debris in the retina, specifically between the retinal pigment epithelium (RPE) and the underlying Bruch’s membrane. Specific sub-RPE deposits known as basal laminar deposits (BLamDs) are a common histopathologic finding in early AMD, but how the deposits are formed is unclear. Shoji Notomi et al. (pp. 23724–23734) examined the role of lysosome-associated membrane protein-2 (LAMP2), which mediates autophagosome and phagosome maturation, in AMD. The authors found that LAMP2 was primarily expressed in RPE cells, and its expression decreased with age in mice as well as in human AMD. Deleting LAMP2 in mice resulted in histopathological changes similar to those seen in AMD, including an increased accumulation of autofluorescent granules and BLamDs and a thickening of Bruch’s membrane. The presence of several key proteins and lipids adjacent to BLamDs in LAMP2-deficient mice also resembled features of human AMD. BLamD accumulation in LAMP2-deficient mice was eventually followed by loss of RPE and photoreceptors. In addition, eyes from AMD patients showed reduced LAMP2 expression and disrupted lysosomal structure relative to normal eyes. According to the authors, LAMP2 plays an important role in RPE function, and the findings suggest that LAMP2 deficiency may contribute to BLamD formation and AMD pathology. — S.R.
Bead making complex off the Florida coast
3D rendering of Raleigh Islands shell rings. Image courtesy of Terry E. Barbour (University of Florida, Gainesville, FL) and the GatorEye Unmanned Flying Laboratory.
Ancient cities in North America, including inland midwestern cities like Cahokia, traded in marine gastropod shells and beads. Although the gastropod shells formed an important part of the economy of the second millennium CE, little is known about the coastal production of shell beads and the transport of shells inland. Terry Barbour, Kenneth Sassaman, et al. (pp. 23493–23498) analyzed high-resolution LiDAR data collected by a drone on Raleigh Island, off the northern Gulf Coast of Florida, revealing a settlement composed of 37 rings of oyster shells. The walls of the residential dwelling rings reached up to 4 meters in height, and archaeological excavation of the rings found evidence of high-production bead making, particularly from the shell of the lightning whelk, a mollusk. Although the bead trade thrived among the chiefdoms of the Mississippian Era, the Raleigh Island complex predates the chiefdoms, suggesting that it arose independently and may have been one of the early suppliers of beads for trade among chiefdoms. According to the authors, the high spatial resolution of LiDAR enabled the discovery of the Raleigh Island complex as well as detailed analysis of the site, which was important to pre-Columbian economies. — P.G.
Cognitive ability, grit, and success
Newly arrived West Point cadets.
The role of noncognitive attributes in predicting success is understudied, compared with the role of cognitive ability. To address this question, Angela Duckworth et al. (pp. 23499–23504) analyzed data on cognitive ability, physical ability, and grit—defined as passion and perseverance for long-term goals of personal significance—from more than 10,000 cadets who entered the US Military Academy at West Point over a decade. Cognitive ability, measured by college entrance exam scores, was negatively correlated with both physical ability, measured by preadmission fitness tests, and grit, measured by a self-report questionnaire completed upon arrival at West Point—findings that underscore the independence of cognitive and noncognitive attributes. Grit was the only attribute that predicted completing West Point’s 6-week intensive initiation training, known as Beast Barracks. Cognitive ability was a strong predictor of academic and military grades, and physical ability was a strong predictor of physical grades. Grit and physical ability were both better than cognitive ability at predicting the probability of graduation. According to the authors, the results suggest that noncognitive and cognitive attributes both contribute significantly to personal achievement. — B.D.
High frequencies and speech perception
DIN web widget. Image courtesy of the hearX Group.
Difficulty understanding speech in noisy environments is a common sign of age-related hearing loss. To determine whether extended high-frequency (EHF) hearing, beyond the clinically tested range, contributes to hearing speech in noise, Lina Motlagh Zadeh et al. (pp. 23753–23759) recruited 116 adults aged 18 to 65 years with clinically normal hearing. Of these listeners, 74 individuals had EHF hearing loss and 39 individuals reported difficulty following a conversation in background noise, such as from a TV or radio. Surprisingly, EHF hearing loss was related to self-reported difficulty in speech perception amid noise. Sixty of the 116 listeners were tested with a digits-in-noise (DIN) test, which is used to measure speech-in-noise hearing. These listeners had better DIN hearing thresholds when noise did not mask EHF information. Although healthy people in their 20s can typically hear tones up to at least 20 kHz, diagnosis of hearing loss is currently based on testing the ability to hear frequencies up to 8 kHz. The findings suggest that EHF hearing loss contributes to difficulty hearing in noisy environments in individuals with otherwise normal hearing. Moreover, EHF hearing may be a predictor of age-related hearing loss at an early age when preventive measures may be effective, according to the authors. — M.S.
Sea-level rise and Paris Agreement pledges
Assateague Island National Seashore after Hurricane Sandy. Image courtesy of Flickr/National Park Service Climate Change Response.
Global mean sea-level rise (GMSLR) is expected to continue long after global mean temperature stabilizes because the key GMSLR contributors respond to warming on time scales ranging from decades to millennia. Alexander Nauels et al. (pp. 23487–23492) used sea-level modeling to estimate the contributions from historical greenhouse gas emissions and those currently pledged under the Paris Agreement to GMSLR until the year 2300. According to the model, if greenhouse gas emissions were eliminated after the end of the Paris Agreement period in 2030, sea level would rise approximately 1 m by 2300 compared with the baseline period of 1986–2005, with approximately 20 cm of GMSLR resulting from emissions pledged under the Paris Agreement. Approximately 25% of the 1-m rise could be attributed to emissions from the top 5 emitters—China, the United States, the European Union, India, and Russia—during the period 1991–2030, and about 11% could be attributed to emissions from these same 5 entities solely during the years of the Paris Agreement, 2016–2030. The results suggest that greenhouse gas emissions in the first decades of the 21st century is likely to affect global sea level for centuries and that limiting long-term GMSLR requires stringent near-term emission reductions, according to the authors. — B.D.