Today’s red junglefowl – the wild ancestors of the domesticated chicken – has become more and more like a chicken. New research suggests that a large proportion of the DNA of wild birds was inherited from chickens, and relatively recently.
Ongoing interbreeding between birds may threaten the future of wild forest fowl populations, researchers reported January 19, 2019, and may hinder humans’ ability to breed better chickens. PLOS Genetics.
red forest fowl (Gallus Gallus) are forest birds native to Southeast Asia and parts of South Asia. Thousands of years ago, humans domesticated birds, possibly in the region’s rice fields (SN: 6/6/22).
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“The chicken is arguably the most important domestic animal on Earth,” says Frank Reindt, an evolutionary biologist at the National University of Singapore. Refers to its global spread and abundance. Chicken is also one of the cheapest sources of animal protein that humans have.
domesticated poultry (Gallus Dominicus) have been known to mate with forest birds near human settlements in Southeast Asia. Given the unknown effects on forest birds and the importance of chickens to humanity, Rheindt and his team wanted to gather more details. Wild jungle fowl contain a reservoir of genetic diversity that can serve as a critical resource for breeding chickens that are resistant to disease or other threats.
The researchers analyzed and compared the genomes – the entire complement of an organism’s DNA – of 63 forest fowl and 51 chickens from across Southeast Asia. Some of the woodland fowl samples came from museum specimens collected from 1874 through 1939, allowing the team to see how the genetic makeup of the woodland fowl changed over time.
Over the past century or so, the genomes of wild forest fowl have become increasingly similar to chickens. The team found that between 20 and 50 percent of the genomes of modern forest fowl originated in chickens. In contrast, many forest birds nearly 100 years old had a share of chicken ancestry on the order of a few percent.
Reindt says the rapid change may come from the expansion of human societies into the region’s wilderness. Most modern forest birds live close to human poultry, with whom they frequently copulate.
Such crossbreeding has become “almost the norm now” for any species domesticated globally, says Reindt, such as dogs crossed with wolves and domestic cats crossed with wild cats. Meanwhile, pigs mingle with wild boars, and ferrets with sparrows.
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Wild populations that mate with domesticated counterparts can pick up physical or behavioral traits that change how hybrids function in their ecosystem, says Claudio Quilodran, a conservation geneticist at the University of Geneva who was not involved in this research.
The effect is likely to be negative, Quilodrán says, since some traits that go into the wild have been refined for human uses, not for survival in the local environment.
Wild forest birds lost their genetic diversity because they also interbred. Bird heterozygosity—a measure of a population’s genetic diversity—is now one-tenth what it was a century ago.
“This result is unexpected at first,” says Reindt. “If you mix one population with another, you will generally expect higher genetic diversity.”
But domesticated poultry has such low genetic diversity that certain copies of forest fowl genes have been swept from populations by a tsunami of genetic homogeneity. Reducing the genetic toolbox of these animals could leave them vulnerable to conservation threats.
“Having so much genetic diversity within a species increases the chance that certain individuals will have the genetic background to adapt to a variety of different environmental changes and diseases,” says Graham Etherington, a computational biologist at the Earlham Institute in Norwich, England. He did not participate in this research.
The shallow jungle fowl gene pool may also mean fewer resources for raising better poultry. Wild relatives’ genes are sometimes used to enhance disease or pest resistance of domesticated crop plants. The genomes of forest fowl could be similarly valuable for this reason.
“If this trend continues unabated, future human generations may only have access to the entire ancestral genetic diversity of chickens in the form of museum specimens,” Reindt says, which could hinder efforts to breed chickens using wild bird genes.
Reindt says some countries like Singapore have started managing bushfowl populations to reduce cross-breeding.