Published in 2013, this paper from Chinese researchers and members of Cornell University used genetic markers to help to determine the past history of grapevine origins.
First, I want to set the stage for understanding (my own) what kind of research the authors conducted in order to come to their conclusion which put dates on the emergence of the genus and the various branches that arose.
Bottomline: Their research concluded that the modern Vitis grape species diverged from earlier relatives about 28 million years ago, that Eurasian grapes diverged from North American ones about 11 million years ago, and finally, that European species diverged from Asian ones about 6 million years ago.
How did they do this?
This study developed and used 27 nuclear gene markers and sequenced 309 accessions of 48 Vitis species, varieties, and four out-groups to:
1) reconstruct a phylogenetic hypothesis of the genus Vitis
2) date important time points in the evolution of Vitis
3) elucidate the biogeographic history of the genus
4) evaluate systematics of Vitis within the framework of phylogeny
Where did the sampling of grape gene markers come from?:1
There is a hypothesis known as the molecular clock.2 The molecular clock records mutations that occur in DNA and provides a kind of ledger. The concept of the molecular clock is a valuable tool in evolutionary studies, currently researchers retain some aspects of the original clock hypothesis while "relaxing" the assumption of a strictly constant rate. The molecular clock must be calibrated based on the organism being studied, relying on some absolute age of some evolutionary divergence event.
In calibrating the molecular clock for the origin of Vitis, the authors chose fossil estimates and distributional inferences that place Vitis into the Paleogene.
The major factors in branching events in the evolution of Vitis include hybridization and recombination. Evolution is arrested by clonal propagation.
With the information above, the stage has been set for the nitty gritty details of the research that will come in Part 2, a future blog.
References:
1. Yizhen Wan, Heidi R Schwaninger, Angela M Baldo, Joanne A Labate, Gan-Yuan Zhong, and Charles J Simon, A phylogenetic analysis of the grape genus (Vitis L.) reveals broad reticulation and concurrent diversification during neogene and quaternary climate change, BMC Evolutionary Biology 2013, 13:141.
2. Scitable, The Molecular Clock and Estimating Species Divergence.
3.Evolutionary genomics of grape (Vitis vinifera ssp. vinifera) domestication
Supplementary Material
Definitions:
Clade: monophyletic, meaning that it contains one ancestor (which can be an organism, a population, or a species) and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct.
Ma: Ages are abbreviated from Latin: Ga (giga-annum) is a billion years, Ma (mega-annum) is a million years, ka (kilo-annum) is a thousand years. (The main argument for using Ma to represent durations is that geologists are used to thinking about numbers meaning ages:70 Ma refers to a time in the Cretaceous.)
Reticulation: is a structure of an identification tree, where there are several possible routes to a correct identification; the tree's "branches" are thus connected into a network, and the key is more robust against errors.
I also consulted several articles to help me understand what I was reading:
- Khan Academy: Phylogenetic Trees
- Wine Folly: Native Wine Grapes of America (Beautiful photos of grapes)
- University of California: Geologic Time Scale
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