- fire ecology — the effects of fire (intensity, frequency, season) on the native plants of eastern Australia
- phylogenetics — the long-term evolutionary history of plant species
- phylogenetic data-analysis methods [see my previous blog: The genealogical world of phylogenetic networks].
This is not from lack of interest in either the phylogenetics or fire ecology of grape-vines, as I do read all of the literature when it appears. It has more to do with the fact that these are complex topics, from my point of view (e.g. the wildfire effects on the wine industry in California in 2020), and they would need to be simplified considerably if I am going to write about them for the general public (in this blog).
Today, however, I am going to try to explain a recent scientific publication about the domestication of grape-vines from their wild progenitors.
The grape cultivars that we currently use in agriculture are (almost) all considered to be a single species (called Vitis vinifera; one of c. 80 species in the genus Vitis). However, their wild ancestors were grouped into a species that we call Vitis sylvestris. Sounds simple doesn’t it? However, even this is actually complicated, because some people think that there is only one species, with two subspecies (Vitis vinifera ssp. vinifera and Vitis vinifera ssp. sylvestris), rather than two separate species (Vitis vinifera and Vitis sylvestris). Don't get involved in this (technical) argument!
Concerning this topic, there was a scientific paper published earlier this year called: Dual domestications and origin of traits in grapevine evolution, published in the journal Science vol. 379 pp. 892–901. Just to give you an idea of the complexity of this particular study, there are 89 authors, from around the world. [Can you imagine trying to co-ordinate this number of people, to agree on a single publication?] The reason for this large number is that they collected 3,525 samples of wild and cultivated grape-vines (2,503 V. vinifera and 1,022 V. sylvestris), and looked in detail at the genetic makeup of each one. *
From this mass of information, a core collection of 2,448 distinctly different grape-vines (1,604 V. vinifera and 844 V. sylvestris) were studied in more detail. They did this by throwing a whole heap of complicated mathematical analyses at the data (many of which I do actually understand!), and came up with some conclusions.
They decided that there are four distinctive genetic groups within V. sylvestris, from distinct geographic regions: Western Asia, the Caucasus, Central Europe, and the Iberian Peninsula. The first pair of these groups was designated as the eastern ecotype (Syl-E) and the second pair as the western ecotype (Syl-W).
They also decided that there are six distinctive genetic groups within cultivated grape-vines (V. vinifera), generally from: Western Asian table grape-vines (CG1), Caucasian wine grape-vines (CG2), Muscat grape-vines (CG3), Balkan wine grape-vines (CG4), Iberian wine grape-vines (CG5), and Western European wine grape-vines (CG6). Note the distinction they make between table grapes and wine grapes.
The idea, then, is to look at the evolutionary history in terms the splitting and merging of these various genetic groups (4+6 = 10 groups) through time, and the time at which these events occurred — this is called a phylogeny. Their phylogeny is shown in the figure immediately above.
I stared at this picture for quite some time, as an expert, and eventually worked out all of what it is saying. [As we scientists like to say: I extracted all of the pertinent information.] However, I challenge you to do the same thing, yourselves; any time you have a few spare hours, have a go!
From your perspective, in trying to understand this, it seems like it will be easier to look at one of their other figures, to work out what the authors concluded about long-term grape-vine history. This is the map shown immediately above, which illustrates the geographic dispersal of the cultivated grape-vine groups.
Their actual description of the pattern [with my extra notes] is:
“In the Pleistocene [epoch, 200,000 to 400,000 years ago], harsh climate drove the separation of wild grape ecotypes caused by continuous habitat fragmentation. Then, domestication occurred concurrently about 11,000 years ago in Western Asia and the Caucasus to yield table [labeled CG1] and wine [labeled CG2] grapevines. The Western Asia domesticates dispersed into Europe with early farmers, introgressed [introgression = the transfer of genetic material from one species into the genome of another] with ancient wild western ecotypes, and subsequently diversified along human migration trails into muscat [CG3] and unique western wine grape [CG4—CG6] ancestries by the late Neolithic [7,000 to 8,000 years ago].”So, there you have it — you will find that this description does actually match the pattern of arrows shown in the map, showing the origin and dispersal of the newly domesticated grape types. **
There is, of course, a lot more information in the paper than this. However, this obvious complexity is why I rarely write about such things in this blog.
* They didn’t collect new samples, but instead got them “from a dozen Eurasian germplasm and private collections”, plus previously obtained genomic data.
** Note the irony of the geographical location where the diversification starts: the Middle East. This is now the location of the biggest alcohol-related conflict that we have; see Tom Wark’s recent review of Wine and the Clash of Civilizations.