Domesticated chickens could wipe out their wild ancestors — by having sex with them

Red junglefowl are under threat from domesticated chickens that want to mate with them, a new study shows. These wild birds, the ancestors of domesticated chickens, risk losing their genetic diversity because they are breeding with farmed chickens that putter around their natural habitat. 

If this crossbreeding continues, it could threaten junglefowl's survival in the future, which would likely have knock-on effects for their domestic counterparts. 

Between 6,000 and 8,000 years ago, humans began to farm red junglefowl (Gallus gallus) for the first time in China and other parts of Southeast Asia. As farmers selectively bred individuals with desirable traits, such as having more meat or producing more eggs, junglefowl gradually evolved into what we now know as chickens (G. g. domesticus), which are a subspecies of red junglefowl. The practice of farming chickens was then eventually adopted all over the globe. 

Today, there are five wild subspecies of red junglefowl: G. g. gallus, which live in India, Bangladesh and Southeast Asia; G. g bankiva, on the Indonesian islands of Java and Sumatra; G. g. jabouillei, native to Vietnam; G. g. murghi, which are found in Bangladesh, India and Pakistan; and G.g. spadiceus, which live in Myanmar and Thailand. All of these subspecies can successfully breed with domesticated chickens, meaning that chickens' genes, which were artificially selected by farmers, can be introduced to wild populations. Scientists call this type of genetic mixing introgressive hybridization, or introgression. 

As chicken farming has intensified around the world due to increased demand for meat and more efficient farming practices, the amount of introgression between chickens and wild junglefowl is believed to have increased significantly, but until now nobody had studied this in detail.

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In a new study, published Jan. 19 in the journal PLOS Genetics, researchers sequenced genomes of 51 chickens and a mix of 63 red junglefowl from the wild subspecies. The sequenced birds included recently deceased individuals as well as remains from older individuals dating to around 100 years ago, which enabled the team to see how much introgression had occurred over the last century. The results showed that between 20% and 50% of wild red junglefowl genes have been inherited from domesticated chickens, and that the rate of genetic mixing has increased over time. 

Despite this increase in shared DNA, the researchers identified eight key genes in chickens that have not been passed on to their wild counterparts. These genes, which play important roles in development, reproduction and vision, were likely key to the domestication of chickens, the researchers wrote in the study. Therefore, the subspecies will likely continue to remain separate for now.

But if this rate of introgression continues, wild red junglefowl subspecies could soon struggle to survive, the researchers warned. Having a reduced genetic pool means that the wild birds may not be able to adapt to changing conditions, such as a loss of habitat or human-caused climate change, which are likely in the future, they said. 

A reduced gene pool in wild junglefowl populations could also have negative implications for domesticated chickens. Currently, researchers can use wild junglefowl as a genetic reservoir to find new genes that can be introduced to domestic breeds — for example, finding genetic variants that make an animal more resistant to a particular disease. But if wild populations have reduced genetic diversity, then this option will be lost.

The team, therefore, believes that attempts should be made to protect wild red junglefowl subspecies from any further introgression. "Our study brings to light the current and ongoing loss of the wild junglefowl genotype, suggesting that efforts may be needed to safeguard its full genetic diversity," researchers wrote.