Nearly 700 Museum Specimens Rewrite the Mallard's Hidden History: Game-Farm Ancestry Has Reshaped Eastern Wild Populations Since the 1940s
Washington — Smithsonian Magazine, published by the Smithsonian Institution, reported on November 5 that researchers from the Smithsonian and the University of Texas at El Paso (UTEP) have reconstructed more than a century of genetic change in the mallard, North America's most familiar waterfowl, using DNA recovered from museum specimens. For over a century, captive-bred mallards have been released into wetlands, often to supplement populations for hunting, and their interbreeding with wild birds has left a genetic legacy that persists decades later.
The research, published this past August in the journal Current Biology and supported by the National Science Foundation (NSF), examined nearly 700 historical mallard specimens from the National Museum of Natural History and 25 other North American natural history museums, collected across the continent between 1818 and 2018. The team recovered DNA from small tissue samples, many from the dried skin of the specimens' toe pads. Lead author Lauren McFarland, a doctoral candidate in biological sciences at UTEP, pieced together the fragmented historical DNA at the Smithsonian's Center for Conservation Genomics, using molecular probes she described as "essentially like fishing hooks" that bind to matching DNA and pull those regions out for sequencing.
The researchers found that game-farm ancestry began appearing in wild mallards during the 1910s and 1920s, coinciding with historical records of captive-bred releases, but did not spread evenly. In the Atlantic Flyway, a major migratory corridor along eastern North America, game-farm ancestry increased sharply beginning in the 1940s and has accounted for approximately 20 percent of the average mallard's genetic ancestry in the region since the 1980s, while populations in the Central and Pacific Flyways have remained largely wild. "It didn't creep up steadily, it arrived in bursts," McFarland said. The analysis also found that captive-bred mallards generally exhibited lower genetic variation, and interbreeding was associated with reduced genetic diversity and increased inbreeding among hybrids.
Robert Fleischer, a Smithsonian evolutionary geneticist who collaborated on the research, said the historical specimens allowed scientists to examine changes that would otherwise be impossible to reconstruct: "I like to think of museums as time machines." Helen James, an ornithologist and the museum's curator of birds, who oversees a collection of more than 600,000 bird specimens, said the naturalists who preserved the birds were documenting where they lived and how they varied: "They weren't expecting that we were going to be getting genomic data from them, but they've become a vast biorepository because of the advances in molecular sequencing lab techniques."
The findings raise questions about the future of wild mallards, including whether game-farm ancestry will persist as releases decline and how inherited domestic traits might influence survival — and demonstrate that even a species as widespread as the mallard is not immune to human-driven genetic change. (Source: Smithsonian Institution)
Source: Smithsonian Institution
Published by GSM · USA (original Chinese edition)
Photo: 图：一只雄性绿头鸭在水面游弋。Charles J. Sharp 摄，CC BY-SA 3.0，经 Wikimedia Commons。 / Photo: A mallard drake swimming. By Charles J. Sharp, CC BY-SA 3.0, via Wikimedia Commons.
