Today’s wild red fowl—the wild progenitors of the domestic chicken—are becoming more chickens. New research suggests that a large proportion of bird DNA is inherited from chickens and is relatively recent.
Ongoing interbreeding between the two birds of prey may threaten the future of wild populations, and even humans’ ability to breed better chicks, researchers report on January 19. PLOS Genetics.
The red bird jumps (A rooster is a rooster) are forest birds native to Southeast Asia and parts of Southeast Asia. Thousands of years ago, humans domesticated the bird, perhaps in the rice fields of the region (SN: 6/6/22).
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“Chickens are arguably the most important domestic animal on earth,” says Frank Rheindt, a national evolutionary biologist at the University of Singapore. It shows their global ubiquity and abundance. Chicken is also one of the cheapest sources of animal protein available to humans.
domestic chickens (G. domestic cock) was known to interbreed with wild birds near human settlements in Southeast Asia. Given the unknown attacks on wild birds and the importance of chicks to humans, Rheindt and his team wanted to collect more details. Wild birds contain a wealth of genetic diversity that could help breed chicks resistant to disease or other threats.
The researchers analyzed and compared the genomes — the complement of an organism’s DNA — from 63 wild birds and 51 chickens from across Southeast Asia. Some of the wildfowl patterns came from museum specimens collected from 1874 through 1939, allowing the team to see how the genetic makeup of wildfowl has changed over time.
Over the last century or so, wild genomes have become more and more like chickens. Between 20 and 50 percent of the genomes of modern wild birds are born in chicks, the team found. In contrast, many of the nearly 100-year-old wild fowl had chicken-ancestor shares in the range of a few percent.
The rapid change probably comes from growing human communities in the desert region, says Rheindt. The last wild birds live in the nearest neighborhood to the young of free people, with whom they often coalesce.
Such interbreeding has become “almost the norm now” for any domesticated species globally, says Rheindt, hybridizing dogs with wolves and crossing cats with wild animals. Pigs, meanwhile, wild boars and ferrets mix with polecats.
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Wild populations that interbreed with their domestic counterparts could adopt physical or behavioral characteristics that change how the hybrids function in their ecosystems, says Claudio Quilodrán, conservation geneticist at the University of Geneva, not involved in this research.
The effect is likely to be negative, Quilodrán says, when certain features are introduced into the wild by human use, not for local survival.
Wild wild birds have lost their genetic diversity as they have also been domesticated. The heterozygosity of birds—a measure of the genetic diversity of a population—is now only one-tenth what it was a century ago.
This is initially counterintuitive, says Rheindt. “If you mix one population with another, you’d generally expect greater genetic diversity.
Domestic chickens, on the other hand, have such low genetic diversity that some versions of wild birds are drawn from a population tsunami of genetic homogeneity. Narrowing the genetic toolkit of these animals may leave them vulnerable to conservation threats.
“Having lots of genetic diversity in a species increases the chance that some individuals are genetically adapted to various environmental changes and diseases,” says Graham Etherington, a computational biologist at the Earlham Institute in Norwich, England, who was not involved in this research.
Higher flight genes could also mean reduced resources for a shorter pool to produce better chicks. Genetics of wild relatives sometimes support the disease or pest resistance of domesticated crop plants. Wild bird genomes can be powerful in a similar way.
“If this trend continues unabated, future generations of humans will only be able to access the universe of genetic diversity of their ancestral chickens in the form of museum specimens,” says Rheindt, who used chicken-based breeding to prevent wild flight genes.
Other countries, such as Singapore, Rheindt says, have begun to manage wild bird populations to reduce mating with chicks.
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