Genetic Analysis Shows Yams Domesticated in West Africa

 

 

MONTPELLIER, FRANCE—Science Magazine reports that a recent genetic survey shows that yams, a key crop in African agriculture, were first domesticated in the Niger River basin. A team led by France’s Institute for Research and Development plant geneticist Nora Scarcelli sequenced 167 genomes of wild and domesticated yams collected from West African countries such as Ghana, Benin, Nigeria, and Cameroon. They found that yams were domesticated from the forest species D. praehensilis. Researchers had believed yams may have been domesticated from a different species that thrives in Africa’s tropical savanna. Previous genetic studies have shown that African rice and the grain pearl millet were also domesticated in the Niger River basin. The finding that yams were first farmed there supports the theory that the region was an important cradle of African agriculture, much like the Fertile Crescent in the Near East. To read about recent research into ancient microbial DNA, go to “Worlds Within Us.”

 

Source: Genetic Analysis Shows Yams Domesticated in West Africa

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Ancient farmers transformed Amazon and left an enduring legacy on the rainforest

Dr. Yoshi Maezumi,

 

Original article:

Popular-archaeology.com

UNIVERSITY OF EXETER—Ancient communities transformed the Amazon thousands of years ago, farming in a way which has had a lasting impact on the rainforest, a major new study* shows.

Farmers had a more profound effect on the supposedly “untouched” rainforest than previously thought, introducing crops to new areas, boosting the number of edible tree species and using fire to improve the nutrient content of soil, experts have found.

The study is the first detailed history of long-term human land use and fire management in this region conducted by archaeologists, paleoecologists, botanists and ecologists. It shows how early Amazon farmers used the land intensively and expanded the types of crops grown, without continuously clearing new areas of the forest for farming when soil nutrients became depleted.

The research team examined charcoal, pollen and plant remains from soil in archaeological sites and sediments from a nearby lake to trace the history of vegetation and fire in eastern Brazil. This provided evidence that maize, sweet potato, manioc and squash were farmed as early as 4,500 years ago in this part of the Amazon. Farmers increased the amount of food they grew by improving the nutrient content of the soil through burning and the addition of manure and food waste. Fish and turtles from rivers were also a key part of the diets at the time.

The findings explain why forests around current archaeological sites in the Amazon have a higher concentration of edible plants.

Dr Yoshi Maezumi, from the University of Exeter, who led the study, said: “People thousands of years ago developed a nutrient rich soil called Amazonian Dark Earths (ADEs). They farmed in a way which involved continuous enrichment and reusing of the soil, rather than expanding the amount of land they clear cut for farming. This was a much more sustainable way of farming.”

The development of ADEs allowed the expansion of maize and other crops, usually only grown near nutrient rich lake and river shores, to be farmed in other areas that generally have very poor soils. This increased the amount of food available for the growing Amazon population at the time.

Dr Maezumi said: “Ancient communities likely did clear some understory trees and weeds for farming, but they maintained a closed canopy forest, enriched in edible plants which could bring them food. This is a very different use of the land to that of today, where large areas of land in the Amazon is cleared and planted for industrial scale grain, soya bean farming and cattle grazing. We hope modern conservationists can learn lessons from indigenous land use in the Amazon to inform management decisions about how to safeguard modern forests.”

Professor Jose Iriarte, from the University of Exeter, said: “The work of early farmers in the Amazon has left an enduring legacy. The way indigenous communities managed the land thousands of years ago still shapes modern forest ecosystems. This is important to remember as modern deforestation and agricultural plantations expand across the Amazon Basin, coupled with the intensification of drought severity driven by warming global temperatures.”

*The legacy of 4,500 years of polyculture agroforestry in the eastern Amazon is published in the journal Nature Plants.

 

 

 

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Research suggests sweet potatoes didn’t originate in the Americas as previously thought

A) Modern distribution of the sweet potato family (yellow line) and genus (white line). B) Fossil leaf of Ipomoea meghalayensis. C) Modern leaf of Ipomoea eriocarpa, showing similar size, shape and vein pattern. Credit: Indiana University

 

 

 

Original Article:

physical.org

 

Sweet potatoes may seem as American as Thanksgiving, but scientists have long debated whether their plant family originated in the Old or New World. New research by an Indiana University paleobotanist suggests it originated in Asia, and much earlier than previously known.

IU Bloomington emeritus professor David Dilcher and colleagues in India identified 57-milion-year-old leaf fossils from eastern India as being from the morning glory family, which includes sweet potatoes and many other plants. The research suggests the family originated in the late Paleocene epoch in the East Gondwana land mass that became part of Asia.

“I think this will change people’s ideas,” Dilcher said. “It will be a data point that is picked up and used in other work where researchers are trying to find the time of the evolution of major groups of flowering plants.”

Previous fossil evidence had suggested the morning glory family may have originated in North America about 35 million years ago. But molecular analyses had supported the idea that it originated earlier and in the Old World. The new research provides evidence for that conclusion.

The discovery also suggests the morning glory family and the nightshade family, which includes potatoes and tomatoes, diverged earlier than previously thought. Together with the recent, separate discovery of 52-million-year-old nightshade fossils in Argentina, it suggests that morning glories developed in the East and nightshades in the West.

The 17 fossils analyzed in the study are the earliest recorded fossils for both the morning glory family, known as Convolvulaceae, and the order Solanales, which includes morning glories and nightshades.

Morning glory fossils are rare because the plants’ soft structure was not easily preserved in rocks.

Dilcher’s collaborators, Gaurav Srivastava and Rakesh C. Mehrotra of India’s Birbal Sahni Institute of Palaeosciences, discovered the fossils in Meghalaya, a state in northeastern India.

The researchers used microscopic analysis of the shape and structure of the leaves, comparing details of the leaf veins and cells with plants in the genus Ipomoea. Using such analysis to examine evolutionary relationships has been a hallmark of Dilcher’s paleobotany research career.

The leaves the researchers studied are in the genus Ipomoea, which includes sweet potato but also hundreds of other plants, most of which don’t produce food for humans.

“We don’t know that these were sweet potatoes,” said Dilcher, emeritus professor in the Department of Earth and Atmospheric Sciences and the Department of Biology in the IU Bloomington College of Arts and Sciences. “We can’t say there were delicious sweet potatoes there. There may have been, or there may not.”

The morning glory family is widely distributed in tropical and subtropical regions and includes about 57 plant genera and 1,880 species. The sweet potato is the world’s second most important root crop, and other members of the family are medicinally and culturally significant.

The study will publish online May 21 in the Proceedings of the National Academies of Science.

 

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All by Itself, the Humble Sweet Potato Colonized the World

 

 

 

Different varieties of sweet potato on display at the International Potato Center in Lima, Peru. The sweet potato originated in the Americas and spread across the globe. Robert Scotland

Many botanists argued that humans must have carried the valuable staple to the Pacific from South America. Not so, according to a new study.

Carl Zimmer APRIL 12, 2018

Nytimes.com

Of all the plants that humanity has turned into crops, none is more puzzling than the sweet potato. Indigenous people of Central and South America grew it on farms for generations, and Europeans discovered it when Christopher Columbus arrived in the Caribbean.

In the 18th century, however, Captain Cook stumbled across sweet potatoes again — over 4,000 miles away, on remote Polynesian islands. European explorers later found them elsewhere in the Pacific, from Hawaii to New Guinea.

The distribution of the plant baffled scientists. How could sweet potatoes arise from a wild ancestor and then wind up scattered across such a wide range? Was it possible that unknown explorers carried it from South America to countless Pacific islands?

An extensive analysis of sweet potato DNA, published on Thursday in Current Biology, comes to a controversial conclusion: Humans had nothing to do with it. The bulky sweet potato spread across the globe long before humans could have played a part — it’s a natural traveler.

Some agricultural experts are skeptical. “This paper does not settle the matter,” said Logan J. Kistler, the curator of archaeogenomics and archaeobotany at the Smithsonian Institution.

Alternative explanations remain on the table, because the new study didn’t provide enough evidence for exactly where sweet potatoes were first domesticated and when they arrived in the Pacific. “We still don’t have a smoking gun,” Dr. Kistler said.

The sweet potato, Ipomoea batatas, is one of the most valuable crops in the world, providing more nutrients per farmed acre than any other staple. It has sustained human communities for centuries. (In North America, it often is referred to as a yam; in fact, yams are a different species originating in Africa and Asia.)

Scientists have offered a number of theories to explain the wide distribution of I. batatas. Some scholars proposed that all sweet potatoes originated in the Americas, and that after Columbus’s voyage, they were spread by Europeans to colonies such as the Philippines. Pacific Islanders acquired the crops from there.

As it turned out, though, Pacific Islanders had been growing the crop for generations by the time Europeans showed up. On one Polynesian island, archaeologists have found sweet potato remains dating back over 700 years.

A radically different hypothesis emerged: Pacific Islanders, masters of open-ocean navigation, picked up sweet potatoes by voyaging to the Americas, long before Columbus’s arrival there. The evidence included a suggestive coincidence: In Peru, some indigenous people call the sweet potato cumara. In New Zealand, it’s kumara.

A potential link between South America and the Pacific was the inspiration for Thor Heyerdahl’s famous 1947 voyage aboard the Kon-Tiki. He built a raft, which he then successfully sailed from Peru to the Easter Islands.

Genetic evidence only complicated the picture. Examining the plant’s DNA, some researchers concluded that sweet potatoes arose only once from a wild ancestor, while other studies indicated that it happened at two different points in history.

According to the latter studies, South Americans domesticated sweet potatoes, which were then acquired by Polynesians. Central Americans domesticated a second variety that later was picked up by Europeans.

Hoping to shed light on the mystery, a team of researchers recently undertook a new study — the biggest survey of sweet potato DNA yet. And they came to a very different conclusion.

“We find very clear evidence that sweet potatoes could arrive in the Pacific by natural means,” said Pablo Muñoz-Rodríguez, a botanist at the University of Oxford. He believes the wild plants traveled thousands of miles across the Pacific without any help from humans.

Mr. Muñoz-Rodríguez and his colleagues visited museums and herbariums around the world to take samples of sweet potato varieties and wild relatives. The researchers used powerful DNA-sequencing technology to gather more genetic material from the plants than possible in earlier studies.

Their research pointed to only one wild plant as the ancestor of all sweet potatoes. The closest wild relative is a weedy flower called Ipomoea trifida that grows around the Caribbean. Its pale purple flowers look a lot like those of the sweet potato.

Instead of a massive, tasty tuber, I. trifida grows only a pencil-thick root. “It’s nothing we could eat,” Mr. Muñoz-Rodríguez said.

The ancestors of sweet potatoes split from I. trifida at least 800,000 years ago, the scientists calculated. To investigate how they arrived in the Pacific, the team headed to the Natural History Museum in London.

The leaves of sweet potatoes that Captain Cook’s crew collected in Polynesia are stored in the museum’s cabinets. The researchers cut bits of the leaves and extracted DNA from them.

The Polynesian sweet potatoes turned out to be genetically unusual — “very different from anything else,” Mr. Muñoz-Rodríguez said.

The sweet potatoes found in Polynesia split off over 111,000 years ago from all other sweet potatoes the researchers studied. Yet humans arrived in New Guinea about 50,000 years ago, and only reached remote Pacific islands in the past few thousand years.

The age of Pacific sweet potatoes made it unlikely that any humans, Spanish or Pacific Islander, carried the species from the Americas, Mr. Muñoz-Rodríguez said.

Traditionally, researchers have been skeptical that a plant like a sweet potato could travel across thousands of miles of ocean. But in recent years, scientists have turned up signs that many plants have made the voyage, floating on the water or carried in bits by birds.

Even before the sweet potato made the journey, its wild relatives traveled the Pacific, the scientists found. One species, the Hawaiian moonflower, lives only in the dry forests of Hawaii — but its closest relatives all live in Mexico.

The scientists estimate that the Hawaiian moonflower separated from its relatives — and made its journey across the Pacific — over a million years ago.

But Tim P. Denham, an archaeologist at the Australian National University who was not involved in the study, found this scenario hard to swallow.

It would suggest that the wild ancestors of sweet potatoes spread across the Pacific and were then domesticated many times over — yet wound up looking the same every time. “This would seem unlikely,” he said.

Dr. Kistler argued that it was still possible that Pacific Islanders voyaged to South America and returned with the sweet potato.

A thousand years ago, they might have encountered many sweet potato varieties on the continent. When Europeans arrived in the 1500s, they likely wiped out much of the crop’s genetic diversity.

As a result, Dr. Kistler said, the surviving sweet potatoes of the Pacific only seem distantly related to the ones in the Americas. If the scientists had done the same study in 1500, Pacific sweet potatoes would have fit right in with other South American varieties.

Dr. Kistler was optimistic that the sweet potato debate would someday be settled. The world’s herbariums contain a vast number of varieties that have yet to be genetically tested.

“There are more than we could look at in a lifetime,” Dr. Kistler said.

For his part, Mr. Muñoz-Rodríguez plans on searching for more wild sweet potato relatives in Central America, hoping to get more clues to how exactly a thin-rooted weed gave rise to an invaluable crop.

Working out the history of crops like this could do more than satisfy our curiosity about the past. Wild plants hold a lot of genetic variants lost when people domesticated crops.

Researchers may find plants they can hybridize with domesticated sweet potatoes and other crops, endowing them with genes for resistance to diseases, or for withstanding climate change.

“Essentially, it’s preserving the gene pool that feeds the world,” Dr. Kistler said.

Caption1 The distribution of the sweet potato plant has baffled scientists. How could the plant arise from a wild ancestor in the Americas and wind up on islands across the Pacific? Karsten Moran for The New York Times

Caption2 Different varieties of sweet potato on display at the International Potato Center in Lima, Peru. The sweet potato originated in the Americas and spread across the globe. Robert Scotland

Link https://www.nytimes.com/2018/04/12/science/sweet-potato-pacific-dna.html

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Epic pre-Columbian voyage suggested by genes, sweet potato’s traded

Epic pre-Columbian voyage suggested by genes

Wooden canoes like this one from Easter Island may have brought Native Americans and Polynesians together.
Polynesians from Easter Island and natives of South America met and mingled long before Europeans voyaged the Pacific, according to a new genetic study of living Easter Islanders. In this week’s issue of Current Biology, researchers argue that the genes point to contact between Native Americans and Easter Islanders before 1500 C.E., 3 centuries after Polynesians settled the island also known as Rapa Nui, famous for its massive stone statues. Although circumstantial evidence had hinted at such contact, this is the first direct human genetic evidence for it.

In the genomes of 27 living Rapa Nui islanders, the team found dashes of European and Native American genetic patterns. The European genetic material made up 16% of the genomes; it was relatively intact and was unevenly spread among the Rapa Nui population, suggesting that genetic recombination, which breaks up segments of DNA, has not been at work for long. Europeans may have introduced their genes in the 19th century, when they settled on the island.

Native American DNA accounted for about 8% of the genomes. Islanders enslaved by Europeans in the 19th century and sent to work in South America could have carried some Native American genes back home, but this genetic legacy appeared much older. The segments were more broken and widely scattered, suggesting a much earlier encounter—between 1300 C.E. and 1500 C.E.

But did Polynesians land on South American beaches, or did Native Americans sail 3500 kilometers into the Pacific to reach Rapa Nui? “Our studies strongly suggest that Native Americans most probably arrived [on Rapa Nui] shortly after the Polynesians,” says team member Erik Thorsby, an immunologist at the University of Oslo. He thinks that could support the controversial theory, posited by Norwegian adventurer Thor Heyerdahl more than a half-century ago, that Native Americans had the skills to move west across the Pacific.

But many scientists say that Pacific currents and Polynesian mastery of the waves make it more likely that the Polynesians were the voyagers. They may have sailed to South America, swapped goods for sweet potatoes and other novelties—and returned to their island with South American women.

Sweet potato was domesticated in the Andean highlands, and researchers recently determined that the crop spread west across Polynesia before Europeans arrived. Another hint of trans-Pacific exchange comes from chicken bones—unknown in the Americas before 1500 C.E.—excavated on a Chilean beach, which some believe predate Christopher Columbus.

Skeptics say that genetic evidence from modern human populations is not enough to prove ancient contact. The genetic clock is often uncertain, says anthropologist Carl Lipo of California State University, Long Beach. “We need ancient DNA from skeletal evidence—not modern evidence—to resolve this question.”

*Clarification, 27 October, 11:50 a.m.: Erik Thorsby is described as supporting the hypothesis that Native Americans voyaged on their own to Easter Island. Thorsby, like most scientists, believes it much more likely that Polynesians brought Native Americans to the island.

By Andrew Lawler 23 October 2014 12:00 pm 9 Comments

news.sciencemag.org

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Clues to Prehistoric Human Exploration Found in Sweet Potato Genome

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Topic: Sweet Potato's

Europeans raced across oceans and continents during the Age of Exploration in search of territory and riches. But when they reached the South Pacific, they found they had been beaten there by a more humble traveler: the sweet potato. Now, a new study suggests that the plant's genetics may be the key to unraveling another great age of exploration, one that predated European expansion by several hundred years and remains an anthropological enigma.

Humans domesticated the sweet potato in the Peruvian highlands about 8000 years ago, and previous generations of scholars believed that Spanish and Portuguese explorers introduced the crop to Southeast Asia and the Pacific beginning in the 16th century. But in recent years, archaeologists and linguists have accumulated evidence supporting another hypothesis: Premodern Polynesian sailors navigated their sophisticated ships all the way to the west coast of South America and brought the sweet potato back home with them. The oldest carbonized sample of the crop found by archaeologists in the Pacific dates to about 1000 C.E.—nearly 500 years before Columbus's first voyage. What's more, the word for "sweet potato" in many Polynesian languages closely resembles the Quechua word for the plant.

Studying the genetic lineage of the sweet potato directly has proved difficult, however. European traders exported varieties of sweet potato from Mexico and the Caribbean to the Pacific, and those breeds mixed with the older Polynesian varieties, obscuring their genetic history. Therefore, it's difficult to apply information culled from modern samples to older varieties without a prehistoric control.

Now a team of researchers working with France's Centre of Evolutionary and Functional Ecology and CIRAD, a French agricultural research and development center, has identified one such temporal control: sweet potato samples preserved in herbariums assembled by the first European explorers to visit many Polynesian islands. The study, which is published online today in the Proceedings of the National Academy of Sciences, provides strong evidence for prehistoric contact between Polynesia and South America.

By analyzing genetic markers specific to sweet potatoes in both modern samples of the plant and older herbarium specimens, the researchers discovered significant differences between varieties found in the western Pacific versus the eastern Pacific. This finding supports the so-called tripartite hypothesis, which argues that the sweet potato was introduced to the region three times: first through premodern contact between Polynesia and South America, then by Spanish traders sailing west from Mexico, and Portuguese traders coming east from the Caribbean. The Spanish and Portuguese varieties ended up in the western Pacific, while the older South American variety dominated in the east, which would explain the genetic differences the French team saw.

The decision to analyze herbarium specimens is "innovative" and provides another piece of strong evidence for the tripartite hypothesis, says archaeologist Patrick Kirch, of the University of California, Berkeley, who was not involved in the study. Lead author Caroline Roullier emphasizes that although her genetic analysis alone doesn't prove that premodern Polynesians made contact with South America, it strongly supports the existing archaeological and linguistic evidence pointing to that conclusion. "It's the combination of all different kinds of proof" that's really convincing, she says. Anthropologist Richard Scaglion of the University of Pittsburgh in Pennsylvania agrees, "All the lines of evidence coming together … really strengthens the case" for Polynesian contact with South America.

Original article:
news.sciencemag.org

By Lizzie Wade, jan 21, 2013

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