Highlights in PNAS

New for December 9, 2020

Anthropology

Differences in ancient Peruvian diets

Early human diets affected regional economies. However, food consumption practices of pre-Hispanic communities in the Central Andes are not well understood. To determine ancient diets in Huaca Prieta and Paredones—two sites in north coastal Peru dating to approximately 7,500 to 4,000 years ago—Tiffiny Tung et al. analyzed teeth from the remains of 21 individuals excavated from Huaca Prieta and nine individuals excavated from Paredones. Although Huaca Prieta and Paredones are only a few hundred meters apart, their communities had significantly different diets. Isotopic analyses revealed that Paredones children primarily consumed maize—likely in the form of a beverage or gruel during the weaning period—suggesting that early uses of maize were influenced by breastfeeding mothers. Dental microwear analyses demonstrated that the diets of Paredones adults were high in abrasives, likely from maize and foods prepared on grinding stones. The diets of Huaca Prieta children and adults were primarily composed of soft food from nonmaize plants and marine resources, such as fish and sea lions. Compared with Huaca Prieta children, Paredones children exhibited greater consumption of maize and terrestrial meat. The findings suggest that diet differences in ancient communities in close proximity may have created opportunities for resource exchange and economic specialization, according to the authors. — M.S.

"Early specialized maritime and maize economies on the north coast of Peru," by Tiffiny A. Tung, Tom D. Dillehay, Robert S. Feranec, and Larisa R. G. DeSantis
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Earth, Atmospheric, and Planetary Sciences

Uncovering tectonic plate movement without fossil help

The origins of mountain belts formed by plate tectonics are typically determined by analyzing fossils located within their strata. However, the limited fossil record of the Precambrian area renders analysis of tectonic plate movement difficult. A. M. Celal ?eng?r et al. reconstructed the tectonic environments of North Africa and the Arabian Peninsula and report the formation of an ancient mountain belt, the Saharides, 500–900 million years ago, before the final collision of east and west Gondwana-Land. To identify essential mountain-building processes, the authors examined the geochemistry and structural geology of the existing Precambrian rock record and attempted to distinguish juvenile from reworked crust material. The samples were not discrete, but part of a belt of mountains formed over a 400-million-year period by subduction and accretion of rocks that simultaneously became stacked by strike-slip faults into large crustal panels. Analysis of magnetic anomalies suggested that the mountain belt may have been bent twice after its formation, similar to the Hercynian double orocline in western Europe. The Saharides’ formation likely added 3–5 million km² of material to the continents. According the authors, the method could be used to reconstruct other complex mountain formations, or orogenic, systems. — T.H.D.

"Reconstructing orogens without biostratigraphy: The Saharides and continental growth during the final assembly of Gondwana-Land," by A. M. Celal ?eng?r, Nalan Lom, Cengiz Zabc?, Gu?rsel Sunal, and Tayfun ?ner
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Earth, Atmospheric, and Planetary Sciences; Ecology

Landscape of ancient Tibet

Sparse fossil records have hampered understanding of the topography of ancient Tibet and its impact on the region’s biodiversity. To unravel Tibet’s ancient environment, Tao Su et al. analyzed fossils of 70 different plant taxa dating to approximately 47 million years ago. The authors excavated the fossils at an elevation of approximately 4,850 meters in central Tibet’s Bangor Basin. During the Middle Eocene, central Tibet exhibited an optimal ecosystem for diverse, subtropical vegetation. The authors report that a heterogeneous, lowland forest in Tibet grew at an elevation of approximately 1,500 meters; this forest was not dominated by any individual species. Frost was rare, and precipitation was largely seasonal under a monsoonal climate. The region also experienced high humidity, short winters, and a mean annual temperature of approximately 19 °C. Tibet’s ancient flora did not resemble contemporaneous flora found in the Indian Plate but instead resembled contemporaneous flora from Germany and the United States. The findings suggest that an east–west running valley persisted for at least 25 million years in central Tibet before giving way to the present elevated plateau, which gradually formed via compression-driven landscape changes, according to the authors. — M.S.

"A Middle Eocene lowland humid subtropical ‘Shangri-La’ ecosystem in central Tibet," by Tao Su, et al.
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Ecology

Why giant pandas roll in manure

Attraction to fecal matter among wild mammals is rare, but Qinling giant pandas have been observed to roll in horse manure. The behavior typically involves a panda sniffing the manure, rubbing against it with the cheek, rolling in the manure, and smearing it over its body. To uncover the purpose of the behavior, Wenliang Zhou, Shilong Yang, Bowen Li, Yonggang Nie, et al. observed 38 horse-manure-rolling behaviors in giant pandas from 2016 to 2017. The frequency of manure-rolling was correlated with the freshness of the manure and with the ambient air temperature, given that almost all events were recorded at temperatures between -5 °C and 15 °C. Hypothesizing that the presence of the chemical compounds beta-caryophyllene and caryophyllene oxide in fresh manure may drive the behavior, the authors found that pandas at the Beijing Zoo in winter preferentially sniffed, rubbed, and smeared hay treated with those compounds. The authors further hypothesized that the compounds may be related to tolerance of cold temperatures and found that mice treated with the compounds exhibited increased cold tolerance. Subsequently, the authors found that beta-caryophyllene and caryophyllene oxide interacted with the pandas’ thermosensitive receptor pathway mediated by the TPRM8 protein and inhibited cold activation of the pathway. According to the authors, manure-rolling may help the pandas acclimatize to cold temperatures. — P.G.

"Why wild giant pandas frequently roll in horse manure," by Wenliang Zhou, Shilong Yang, Bowen Li, Yonggang Nie, et al.
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Ecology

Mitigating conflict between cheetahs and humans

Conflict between humans and wildlife leads to declining global populations of carnivores. However, insight into the socio-spatial organization of species in conflict may provide nonlethal solutions to human–carnivore conflict. Between 2007 and 2018, Joerg Melzheimer et al. analyzed the landscape use and social activity of 106 GPS-collared wild cheetahs in central Namibia, where cheetahs are known to prey on farmland cattle calves. Cheetahs use scent-marking sites to communicate with each other, and such sites, defined in the study as communication hubs, were clustered in certain areas. Communication hubs were located in territorial areas and distributed across the landscape in a consistent pattern. Cheetahs often visited hubs for information exchange, establishing hotspots of cheetah abundance and activity. The annual number of calves lost to cheetah predation decreased by approximately 86% when farmers shifted breeding herds away from known hubs. Instead of following the herds, cheetahs preyed on local wildlife within hubs. The findings suggest that efforts to mitigate human–cheetah conflict should focus on conflict-prone areas rather than individual cheetahs, according to the authors. — M.S.

"Communication hubs of an asocial cat are the source of a human–carnivore conflict and key to its solution," by Joerg Melzheimer, et al.
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Ecology; Sustainability Science

European settlement and seabird decline

Seabirds are key members of marine ecosystems but often lack long-term monitoring, potentially hindering conservation goals. Matthew Duda et al. report a reconstruction of approximately 5,800 years of seabird population dynamics on an Atlantic island that links expanding human settlement to severe population decline of the vulnerable seabird, Leach’s Storm-petrel. The authors examined sediment cores from a pond on Grand Colombier Island in the Northwest Atlantic, home to a large breeding colony of storm-petrels. The authors analyzed the cores, representing around 5,800 years of activity, for evidence of avian waste products, such as guano, feathers, and eggshells. The authors estimated population size based on five proxies, including the composition of aquatic diatom taxa that are directly influenced by avian inputs and the concentrations of specific trace elements that would have been predominantly introduced by the birds. The results suggest that the population experienced substantial natural fluctuations until disruption occurred at the start of the 19th century, concurrent with European settlement. Currently, the island supports only around 16% of the population that was likely supported around 740 years ago. According to the authors, paleoecological approaches can help determine current rates of ecological loss and protect critical habitat. — T.H.D.

"Linking 19th century European settlement to the disruption of a seabird’s natural population dynamics," by Matthew P. Duda, et al.
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Some of the highlights have previously appeared on the PNAS media tipsheet. The articles in PNAS report original research by independent authors and do not necessarily represent the view of the National Academy of Sciences.

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