Category: Domestication

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A maize tour

SIRGEALC over, Marleni, David and I headed for CIMMYT, the International Maize and Wheat Improvement Centre. That’s in Texcoco, about an hour’s drive from the hotel where we were staying in Mexico City (or three hours, unfortunately, on the way back). It turned out to be something of a maize odyssey. I’ll tell the story in pictures.

When we got to Texcoco, it was too early for lunch, but that didn’t stop us spending some time in the market sampling the local cuisine, as the quesadillas there are famous. This lady certainly made us some great ones. Note the two types of maize she’s using.

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Domesticated ants?

This I’d like to see. A television documentary depicts in loving detail a battle between red driver ants and termites. The amazing part: the driver ants are under the “control” of the Mofu people of northern Cameroon, who use the ants to protect their houses and harvests. Read all about it at The Ant Room. Better yet, watch the TV show and tell us more.

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Parasites push promiscuity

Many hermaphrodite plants (and some animals) — including many crops — have what is called a mixed mating reproductive strategy. That means they reproduce by both self- and cross-fertilization, with important consequences for the amount and structure of their genetic variation. The prevalence of mixed mating systems is surprising because inbreeding depression should work to get rid of self-fertilization, resulting in “pure strategies of either outcrossing or selfing.” Now a new study suggests that its natural enemies — pests, parasites, herbivores, etc. — may have a strong effect on the evolution of a plant’s mating systems:

For example, enemies may alter the availability of mates in a population, which may have direct consequences for victim mating system evolution. Enemies may also influence the expression of traits that are important for mating system evolution, thereby improving the evolutionary stability of mixed mating as a reproductive system.

Thus the dynamics of the interactions between a species and the biodiversity that surrounds it can counter the effects of inbreeding depression and lead to the stability of an otherwise doomed evolutionary strategy. I wonder how important this has been in the evolution of agrobiodiversity. After all, concentrating plants in dense near-monocultures like agriculture does is a boon to natural enemies.

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Reinventing the wheel

More evidence of multiple independent domestication events. Previous work has shown such a pattern for rice in Asia and cucurbits in the America. Now it’s the turn of barley in Eurasia. A paper just out ((Saisho, Daisuke, Purugganan, Michael. (2007) Molecular phylogeography of domesticated barley traces expansion of agriculture in the Old World. Genetics.)) looked at both sequences of 5 genes and also morphological traits in a geographically widespread set of 250-odd landraces. ((From a Japanese university genebank.))

The results suggest that the crop was first domesticated 10,000 years ago somewhere in the Fertile Crescent, from whence it spread to Europe, North Africa and Ethiopia (the material from Ethiopia was somewhat distinct, as has already been documented). However, there was apparently also a second domestication, much later. It occurred in the region encompassing southern Central Asia, the eastern Iranian plataeau and the edge of the Indian subcontinent, and it is material from here that spread eastward starting maybe 2,500 years ago, possibly along the Silk Road, to give rise to the barleys of India, the Himalayas and China.

This is not an unusual pattern in Eurasian agricultural biodiversity. Sheep and cattle DNA data also show “two highly divergent lineages that distinguish European and Asian types, indicating a second independent evolution of these livestock species outside the Near East.” Not unusual, but somewhat puzzling. As the barley authors conclude:

It remains unclear why different cultures sought to re-invent these domesticated species several times rather than simply obtain them through diffusion from other farming societies.

The authors of the barley study speculate that the second domestication happened either because of the transmission of knowledge, or as an independent innovation. I find the second option a bit hard to take. Could it be that the results of the first domestication effort were just not adapted to conditions outside the Fertile Crescent, or there was a barrier to their diffusion? Or maybe it was just a matter of pride for the inhabitants of the Iranian plateau to have their own agrobiodiversity?