JANUARY 28, 2020

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www.pnas.org/cgi/doi/10.1073/iti0420117 PNAS | January 28, 2020 | vol. 117 | no. 4 | 1821–1823

Juvenile ornamentation in American coots

Ornamental traits, such as bright-colored plumage, are known to benefit courtship and increase mating success in animals. However, the evolutionary advantage of juvenile ornamentation is unclear. To explore links between juvenile ornamentation and evolutionary fitness, Bruce Lyon and Daizaburo Shizuka (pp. 2056–2064) analyzed variations in the brightness, chroma, and hue in the red plumage of American coot chicks between and within brood families. The coots were studied at five Canadian wet-

lands between 2005 and 2008. Coots lay their eggs in each other’s nests, and the plumage of parasitic chicks was a duller red than the plumage of host chicks. The authors posited that parasitic coots do not use ornamentation to dupe host parents into caring for them. The authors found that within families, later-hatched chicks were darker and redder than earlier-hatched chicks. Compared with chicks of the duller hue, redder chicks were more likely to receive preferential treatment and increased portions of food from parents. The findings suggest that ornamentation in juvenile coots allows parents to determine which chicks would benefit most from additional care and nutrition. Further, color may provide cues to the ages and sizes of chicks, according to the authors. — M.S.

Sea-level rise and land subsidence in the Ganges–Brahmaputra– Meghna deltaThe Ganges–Brahmaputra–Meghna delta, cover-ing most of Bangladesh and part of eastern India, is highly vulnerable to climate-driven sea-level rise. Land subsidence can exacerbate the effects of sea-level rise, but disentangling the contributions of sea-level rise, land subsidence, and river dynamics to relative water level presents a challenge. Mélanie Becker et al. (pp. 1867–1876) analyzed 101 monthly stream and tide gauge records across the delta from the Bangladesh Water Development Board and the Permanent Service for Mean Sea Level database. By regionally aggregating the records to filter local effects, the authors obtained robust esti-mates of variations in relative water level (RWL) from 1968 to 2012. During this period, RWL in the delta increased by approximately 3 mm/year on average,

Three newly hatched American coot chicks.

The Ganges–Brahmaputra–Meghna delta. Image courtesy of Wikimedia Commons/NASA.

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similar to or slightly faster than the rate of global mean sea-level increase during the same period. By combining the RWL estimates with satellite altimetry measurements of absolute sea level during 1993–2012, the authors estimated maximum expected land subsidence rates in the range of 1 to 7 mm/year. If these subsidence rates continue through the end of the current century, then the relative sea-level rise in the delta by 2100 could reach 140 cm in some regions, doubling the rise previously pro-jected under a greenhouse gas emission mitigation scenario, according to the authors. — B.D.

Universal experiences associated with musicMusic bears cultural significance around the world, but whether music evokes specific emotions in universal ways is unclear. Alan Cowen, Xia Fang, et al. (pp. 1924–1934) recruited 895 participants from China and 1,011 participants from the United States to listen to subsets of 1,841 5-second, non-lyrical music samples. The music library was com-piled by 111 individuals from the United States who contributed samples determined to evoke a range of subjective feelings. On average, participants lis-tened to 42 samples and reported feelings evoked by each sample. Compared with broad evaluations, such as arousal and valence, specific feelings, such as triumph and joy, were more universal, with most music samples being associated with similar feelings in both countries. In a subsequent experiment, 22 individuals from the United States compiled 138

modern Western music samples, and six individuals from China compiled 189 traditional Chinese music samples. The 5-second samples were evaluated by 580 participants from the United States and 363 participants from China, and the results mirrored the first experiment. The findings suggest that specific

feelings are more universal than broader evalua-tions, which are culture-specific, according to the authors. — M.S.

Ages of interstellar dust particlesInterstellar dust, a small but important fraction of matter in space, cannot be dated by astronomical observation or radioactive decay, leaving informa-tion on the ages and longevity of interstellar dust par-ticles unknown. Philipp Heck et al. (pp. 1884–1889) analyzed 40 grains of silicon carbide, incorporated

into the Murchison CM2 meteorite 4.6 billion years ago, for neon isotopes produced by interactions with cosmic rays. Rates of formation of such cosmo-genic isotopes can be used to date the particles. Sixty percent of the particles returned ages of less than 300 million years before the formation of the Solar System, compatible with estimates of interstel-lar lifetimes of 100–200 million years. However, par-ticles with ages more than 1 billion years before the formation of the Solar System suggest that these grains were shielded in dense clumps that helped the particles survive supernova shockwaves in the interstellar medium. Some of the grains’ histories may have included aggregates, including mantles of ices or organic compounds. According to the authors, cosmogenic neon dating used in the study is a viable method for obtaining information about the galaxy prior to the formation of the Sun. — P.G.

Susceptibility to opioid use disorderUp to 10% of patients who are prescribed opioids for chronic pain develop an opioid use disorder. The molecular mechanisms underlying individual differ-ences in susceptibility to opioid use disorder have been unclear. Marsida Kallupi et al. (pp. 2140–2148) used a heterogeneous rat population to mimic

1822 | www.pnas.org/cgi/doi/10.1073/iti0420117 In this issue

Music evokes specific feelings across cultures. Image courtesy of Pixabay/stevepb.

Scanning electron micrograph of a dated presolar silicon carbide grain. The grain is ∼8 μm in its longest dimension.

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behavioral and genetic diversity among humans. The rats were allowed to press a lever to self- administer intravenous infusions of oxycodone up to 12 hours each day for 3 weeks and were divided into high-addicted and low-addicted groups. Compared with rats never exposed to oxycodone, high-addicted rats showed lower levels of the endogenous opioid-like peptide nociceptin in the brain’s central nucleus of the amygdala (CeA). Com-pared with low-addicted rats, high-addicted rats also showed higher spontaneous activity of CeA neurons that release the inhibitory brain chemical γ-aminobutyric acid (GABA). Nociceptin adminis-tration decreased the activity of these neurons to a greater extent in CeA slices from high-addicted rats compared with low-addicted rats. Moreover, noci-ceptin injections into the CeA reduced oxycodone self-administration in high-addicted rats, but not in low-addicted rats. According to the authors, the findings suggest that opioids may lead to addiction in susceptible individuals by decreasing nociceptin levels in the CeA and subsequently increasing GABA release. In addition, the results suggest that small molecules targeting the nociceptin system may help treat opioid use disorder. — J.W.

How ancient trees maintain longevityTrees can live for centuries or even millennia, but the molecular and metabolic mechanisms underlying their long lifespans are unclear. Li Wang, Jiawen Cui, Biao Jin, et al. (pp. 2201–2210) examined age-related changes in the vascular cambium, the main growth tissue in the stems and roots, of 15- to 667-year-old Ginkgo biloba trees. Increasing age was not accom-panied by a significant decrease in leaf area, photo-synthetic efficiency, seed germination rate, or basal area increment, which is a reliable indicator of tree

growth based on tree ring analysis. RNA sequenc-ing of the vascular cambium revealed an age-related decline in the expression of genes involved in cell division, expansion, and differentiation—processes important for vascular tissue growth. However, these changes were not accompanied by a significant

increase in the expression of genes related to senes-cence, which is the final developmental stage. More-over, the vascular cambium of young and old trees displayed similar expression levels for genes associ-ated with the biosynthesis of protective metabolites called flavonoids, as well as other resistance genes involved in defending against stress related to fac-tors such as pathogens or drought. According to the authors, the findings suggest that old trees may stay healthy by preventing senescence and maintaining robust resistance to external stress. — J.W.

www.pnas.org/cgi/doi/10.1073/iti0420117 PNAS | January 28, 2020 | vol. 117 | no. 4 | 1823

G. biloba. Image courtesy of Wikimedia Commons/Dinkum.

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