Dog fight over canine origins

We’ve pointed briefly to recent studies on the origins of the domestic dog, where two schools of thought hold sway. The conventional version offers east Asia — China, more or less — as the centre of dog diversity and, by implication, the place where dogs were first domesticated. An apostate view is that dogs were domesticated in Africa and perhaps in Europe too.

There’s no clear resolution in sight yet, but it looks as if the Chinese dog may be on top. A news report in Science gives details of (and links to) a new and more detailed study from Peter Savolainen and his team:

The data reaffirm a single site for domestication and pinpoint the origin of the domesticated dog to a region south of the Yangtze River, where wolf taming was quite common, Savolainen’s team reports today in Molecular Biology and Evolution. That’s where the largest number of similar groupings of DNA, called haplogroups, is found. As the researchers looked at dogs farther from this region, they saw fewer haplogroups; Europe had only four, for example. “The gene pool we are finding in Europe and Africa are a subset of the South Chinese gene pool,” says Savolainen.

But the African dogs aren’t rolling over yet.

Carles Vilà of the Biology Station of Doñana-CSIC in Seville, Spain … points out that other genetic studies suggest dogs date back at least 20,000 years and that archaeological remains of dogs in Europe are almost as old. … “I’m not convinced by the results,” he says, “and I do not think this is the last that we will hear about the time and place of the domestication of dogs.”

That seems certain. Back in the days before DNA a multiple-origins theory was all the rage, but then, it was for H. sapiens too.

Nibbles: European agricultural origins, Drought, Native American ranching, Sorghum, Anthocyanins in apples, Dog coat, Pear cider

Upstream blast

ResearchBlogging.org Blast is one of the worst rice diseases. I believe that, thanks to the breeders, most modern varieties have decent levels of resistance. After all, they can be used in varietal mixtures to protect traditional glutinous rice varieties from blast. ((Zhu, Y., Chen, H., Fan, J., Wang, Y., Li, Y., Chen, J., Fan, J., Yang, S., Hu, L., Leung, H., Mew, T., Teng, P., Wang, Z., & Mundt, C. (2000). Genetic diversity and disease control in rice. Nature, 406 (6797), 718-722 DOI: 10.1038/35021046 Also see this post.)) Unfortunately, much of this resistance is not durable, because the pathogen overcomes it with time.

For a long time, durable resistance has been known to exist in some Japanese varieties. But these varieties have not been useful for resistance breeding, as the resistant parent also brought along undesired characteristics: the offspring always had poor eating quality.

Shuichi Fukuoka and colleagues have found out why. They report in Science ((Fukuoka, S., Saka, N., Koga, H., Ono, K., Shimizu, T., Ebana, K., Hayashi, N., Takahashi, A., Hirochika, H., Okuno, K., & Yano, M. (2009). Loss of Function of a Proline-Containing Protein Confers Durable Disease Resistance in Rice Science, 325 (5943), 998-1001 DOI: 10.1126/science.1175550
see also Normile, D. (2009). New Strategy Promises Lasting Resistance to a Rice Plague Science, 325 (5943), 925-925 DOI: 10.1126/science.325_925)) that it is because of a tight genetic linkage. Resistance is conferred by the Pi21 locus, and:

The eating quality of plants carrying the elite cultivar’s chromosomal sequence from a point less than 2.4 kb downstream of the Pi21 locus was equivalent to that of the elite cultivar, and the plants showed a high level of blast resistance. In contrast, plants carrying the donor chromosomal sequence up to 37 kb downstream of the Pi21 locus showed inferior eating quality.

By crossing in just the right bit of the chromosome, and making sure that the neighboring areas do not tag along, resistance can now be transferred, without spoiling the taste.

Nibbles: Cacao, Soil mapping, Rice terraces, Maize, Cereus