Seen from the air, Channel Country resembles a vibrant and vast tapestry, with a network of waterways crisscrossing the land. Spread across more than 280,000 square kilometers in outback Australia, it is one of the world’s last free-flowing desert river systems.
In the heart of Channel Country, in southwest Queensland, live the Mithaka people whose ancestors over at least the past 3,000 years played a key role in the development of a transcontinental trade and exchange system. Plants were a central part of the economy of the Mithaka people, with at least 200 different species used for food, medicine, materials and ceremonial purposes.
In a new paper published in Nature Communications, we reveal important new information about the genetic complexity of one particular food source from the region: channel millet (Echinochloa turneriana).
The traits we found are often associated with domestication.
Deep importance of plants in Mithaka life
How people managed and interacted with plants is an area that’s slowly starting to gain momentum in Australian archaeology.
Genomics has played a fundamental role in increasing understanding of relationships between people and plants in several regions of the world, including the Americas and Asia. It has the potential to shed light on how humans influenced vegetation communities in Australia, though much of the detailed research is yet to be done.
The few genetic studies undertaken in Australia, working with Aboriginal people on understanding their history of plant interactions, have revealed important new insights.
One outstanding example is the discovery that Aboriginal people in northeast New South Wales and southeast Queensland deliberately dispersed the black bean (Castanospermum australe), a valuable native food source.
The Mithaka people have a rich archaeological record that highlights the deep importance of plants in everyday life. Our previous research has identified hundreds of grinding stone quarries used to process the seeds of native grasses, herbs, shrubs and trees — evidence of sophisticated knowledge of local ecosystems and food resources.
Together, these sites form an interconnected cultural landscape of exceptional significance, recently recognized and added to the National Heritage List.
Untangling complex genetics
Our new study builds on this foundation.
Channel millet grows more than a meter tall. A robust grass, it flourishes after flooding, forming extensive fields of waving brown seedheads. At such times in the past, it was an important food source for Aboriginal people.
The explorer Augustus Gregory came upon “fields of 1,000 acres of millet” on the Cooper Creek floodplain in 1884, and described people cutting the stalk halfway up. Early pastoralist and writer Alice Duncan-Kemp described the processing of “ugar” or “egar” (grass seeds resembling canary seeds) by Aboriginal women on the Diamantina River.
We first sequenced the DNA in the channel millet. When we analyzed the genome, we found it to be highly complex. While humans and many plants have two copies of each chromosome (one from the father and one from the mother), this plant has 12 copies of each chromosome.
This is called polyploidy, in which an organism acquires multiple sets of chromosomes, typically through accidents of reproduction or through hybridization.
Large numbers of copies of each chromosome are common in domesticated crops such as wheat, rice and sugarcane. It’s not a smoking gun for domestication; in fact, natural polyploidy has been occurring for millions of years through the processes of chromosome duplication and hybridization.
People, however, have greatly accelerated and exploited the process, sometimes accidentally, but in more recent history deliberately, inducing chromosome doubling to produce crops with larger fruits, greater vigor and improved resilience.
This novel genetic pattern may explain how this plant survives the bust and boom environment in which it grows. Populations of channel millet are decimated during extended dry periods. But they survive as underground seeds that germinate rapidly in periods when floodwaters flow across the region.
Multiple copies of each chromosome may help these populations endure the dramatic fluctuations of life in the Channel Country. Like the hybrid crops prized by farmers, plants with extra chromosome sets can be especially vigorous, giving them a genetic toolkit that helps them survive and thrive in an unpredictable environment.
More than natural selection?
Natural selection may not be the only force that has contributed to the evolution of such unusual genetics.
This plant has large seeds, making it an attractive food source. Like other grass species such as wheat, rice and corn that have been domesticated by people in the past, it also shows little shattering (shedding of the mature seed). This means it is quite efficient to harvest, with seeds remaining attached to the plant at harvest.
Human harvest, storage and consumption may have contributed to the evolution of this unique plant. Harvest will have favored large seeds that did not shatter.
Human consumption may have contributed to population bottlenecks in the ancestors of modern channel millet, while storage may have ensured survival of at least some seeds during extended dry periods. Studies of population variation and other species in the area will be needed to better define these impacts.
Informing knowledge for future foods
Today, Mithaka people are keen to learn more about plants such as channel millet, and how past human interactions with these species may inform knowledge for future foods.
Our future research will link plant genetics with evidence from ancient fireplaces and shell midden sites, plant residues from grinding stones and pollen cores from waterholes targeting specific landscapes in Mithaka country.
Combined with Indigenous knowledge, this research will help build a clearer picture of how Mithaka people actively shaped — and were shaped by — the vegetation communities around them over thousands of years.
Michael Westaway, Professor of Archaeology and Biological Anthropology, School of Social Science, The University of Queensland; Jennifer Silcock, Post-doctoral Research Fellow, School of the Environment, The University of Queensland; Rahul Chandora, Ph.D. Student, Centre for Crop Science, The University of Queensland; Robert Henry, Director, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland; Sammi Blinco, Director, Mithaka Aboriginal Corporation, Indigenous Knowledge, and Shawnee Gorringe, Admin & Research Support at Mithaka Aboriginal Corporation, Indigenous Knowledge
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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