May 27, 2010

Origin of domestic chickens (Sawai et al. 2010)

PLoS ONE 5(5): e10639. doi:10.1371/journal.pone.0010639

The Origin and Genetic Variation of Domestic Chickens with Special Reference to Junglefowls Gallus g. gallus and G. varius

Hiromi Sawai et al.

It is postulated that chickens (Gallus gallus domesticus) became domesticated from wild junglefowls in Southeast Asia nearly 10,000 years ago. Based on 19 individual samples covering various chicken breeds, red junglefowl (G. g. gallus), and green junglefowl (G. varius), we address the origin of domestic chickens, the relative roles of ancestral polymorphisms and introgression, and the effects of artificial selection on the domestic chicken genome. DNA sequences from 30 introns at 25 nuclear loci are determined for both diploid chromosomes from a majority of samples. The phylogenetic analysis shows that the DNA sequences of chickens, red and green junglefowls formed reciprocally monophyletic clusters. The Markov chain Monte Carlo simulation further reveals that domestic chickens diverged from red junglefowl 58,000±16,000 years ago, well before the archeological dating of domestication, and that their common ancestor in turn diverged from green junglefowl 3.6 million years ago. Several shared haplotypes nonetheless found between green junglefowl and chickens are attributed to recent unidirectional introgression of chickens into green junglefowl. Shared haplotypes are more frequently found between red junglefowl and chickens, which are attributed to both introgression and ancestral polymorphisms. Within each chicken breed, there is an excess of homozygosity, but there is no significant reduction in the nucleotide diversity. Phenotypic modifications of chicken breeds as a result of artificial selection appear to stem from ancestral polymorphisms at a limited number of genetic loci.

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6 comments:

Peter Princeton said...

junglefowls amd chickens look alike.

terryt said...

"domestic chickens diverged from red junglefowl 58,000±16,000 years ago, well before the archeological dating of domestication, and that their common ancestor in turn diverged from green junglefowl 3.6 million years ago".

The last bit makes sense, red and green jungle fowl diverged more than 3 million years ago. The fact they readily interbreed is very interesting. They are birds, but does that figure mean birds speciate much more slowly than mammals?

As to the 60,000 year separation between red jungle fowl and domestic chooks. That suggests that domestic chooks are a third species (or subspecies), now extinct in the wild.

Mark Morgan said...

It's difficult for me to see how chickens could have been domesticated so long ago, though I've been surprised before. But I wonder if the divergence dates correspond, not to the domestication of red jungefowl, but rather to the isolation of a population somewhere in Sundaland following glacial retreat. If these isolated fowl were subsequently domesticated, they would still show the deep divergence.

Andrew Oh-Willeke said...

Divergence don't necessarily imply domestication, which seems in the case of the chicken to be 9000 years ago, give or take.

But, one could imagine pre-domestication interaction with the modern human populations that arrived in the area around then.

For example, perhaps early modern human hunter-gatherers stole eggs from proto-chickens and had a taboo against hunting them for thousands of years, influencing their evolution, long before they were kept in coops or hunted for dinner.

terryt said...

"Divergence don't necessarily imply domestication"

Exactly, but I don't think domestication of any sort would be involved here (if the data is correct, of course). I suspect Mark is correct, 'But I wonder if the divergence dates correspond ... to the isolation of a population somewhere in Sundaland following glacial retreat". No members of this popultion survive in the wild, although Indian (red), Sri Lankan (green, I think) and Javan jungle fowl survive in the wild.

J. Lyon Layden said...

The study and the comments absolutely amaze me. Where do they get 10,000 years? Oh, that's right- nothing can have happened before 10,000 years or some scientists won't get their tenures I guess. And the comments...I'm just blown away. A taboo against hunting chickens? The chickens were isolated in Sundaland and then we got all of them and then didn't miss a single pair sometime after 10,000 years ago? Give me a break! Hominids were introducing animal species to Indonesian islands 37,000 years ago and probably longer. We already know that. They had already domesticated tubers in the Solomon Islands by then. It doesn't take a genius to find some hatchlings in the wild and feed them. And one of the microcephalin genes that underwent massive selection in our genome 6000 years ago comes from South-East Asia. If you can't connect the dots I dunno what to tell you.