Evolution of the genus CamelinaDespite rising interest in the biofuel crop Camelina sativa, little is known about other species in the genus. In fact, there's discrepancies over how many species exist, and even what each species looks like. Furthermore, it's unclear how different species are related and how they evolved. Answering these questions would have been unfeasible without extensive collections in areas of high diversity. Collections in the highly under-represented region of Turkey, Georgia and Armenia provides a base for which these questions can be answered.
|
C. laxa growing wild in Armenia
|
Camelina inflorescence
|
Some species (C. microcarpa and C. rumelica) have become world-wide weeds that can be found on nearly every continent. Even the domesticated C. sativa has a history of weediness. In fact, one common name for C. sativa is false-flax, because it took on many characters of flax in order to be undetected and contaminate flax seed collections. Through an evolutionary process called Vavilovian mimicry, C. sativa seeds became indistinguishable in size from flax seeds, thus becoming a difficult weed to remove from flax fields and seed harvests.
One difficulty in studying the diversity of the genus is a massive collection bias of Camelina species from around the world. There are tens of thousands of collections of Camelina but most occur in Western Europe and North America; both are regions of low Camelina diversity. This is one reason why my collections in the region of highest diversity are so important; they are under-represented in the collection records and include many rare species. Leveraging these collections, we have discovered that C. sativa is likely domesticated from the wild C. microcarpa (Brock et al., 2018) |
|
The domestication of C. sativa likely occurred several thousand years ago in Europe, although it's unclear if there was a single domestication event or multiple. Some of the earliest archaeological evidence of Camelina seeds was found in Armenia dated to over 6,000 years ago (Hovsepyan and Willcox, 2008) indicating a long history of use. Its presence is known in France as far back as 3,000 years ago but no indication of cultivation in France until the 5th century B.C. (Bouby, 1998). This leaves open the possibility that as Camelina spread as a weed across Europe and Asia, people began to select for traits independently.
|
Zorats Karer, Armenia
|
|
Camelina has variable genome sizes - the result of polyploidy. This condition is defined by having extra sets of chromosomes; either the result of genome doubling (autopolyploidy) or hybridization of two species (allopolyploidy). Ploidy levels in the group range from diploid (two chromosome sets) to hexaploid (six chromosome sets). It's not clear which species may be autopolyploid and which may be allopolyploid, how long ago these events occurred, or even if there are different ploidy levels within the same species. Polyploidy often causes a gene-dosage effect that results in bigger plants, higher expression of certain pathways (e.g. oil production), and also gives organisms a larger set of tools (i.e. genes) to cope with different environmental conditions. This likely explains why Camelina species have been so successful in colonizing new continents and habitats.
|
|
Several species may have become extinct in the last few hundred years. One such species is the very intriguing C. anomala, which has an appropriate name considering it's the only species in the genus with siliques instead of silicles (i.e. its fruits are longer than they are wide). Unfortunately, this specimen was only collected a couple of times in the 1800's, and hasn't been seen since (that we know of). In 2012 I retraced the steps of Swiss botanist Pierre Boissier and German Heinrich Haussknecht to find any relics of the type C. anomala, described in Syria in 1865. Unfortunately, there was no trace of C. anomala or any other Camelina. The area, now modern day Turkey around Gaziantep, was transformed by agriculture and is now famous for pistachio production. The silique trait of C. anomala would have been potentially valuable for agricultural improvement of C. sativa, as larger fruits yield more seed. Furthermore, this very unique plant may have once been rather common, and could be a missing piece in the story of the evolution of the crop C. sativa. Although an inconspicuous weed, this is a great example of the importance of species conservation - once a species is extinct, so too are the useful traits it harbors.
|
C. anomala at BGBM, Germany
|
|
I'm deeply fascinated by the story of Camelina, and that's why I've decided to focus on the evolutionary history and diversity of the group. Its history as an old-world crop and flax-weed compel me to dig deeper, make more collections, and tell more stories about how this plant evolved.
|
References:
Bouby, L. (1998). Two early finds of gold-of-pleasure (Camelina sp.) in middle Neolithic and Chalcolithic sites in western France. Antiquity, 72(276), 391–397. http://doi.org/10.1017/S0003598X0008666X
Brock J., Donmez A., Beilstein M., Olsen M. 2018. Phylogenetics of Camelina Crantz. (Brassicaceae) and insights on the origin of gold-of-pleasure (Camelina sativa). Molecular Phylogenetics and Evolution.
Hovsepyan R., Willcox G. 2008. The earliest finds of cultivated plants in Armenia: evidence from charred remains and crop processing residues in pisé from the Neolithic settlements of Aratashen and Aknashen. Vegetation History and Archaeobotany, v.17, s.1, pp. 63-71.
Brock J., Donmez A., Beilstein M., Olsen M. 2018. Phylogenetics of Camelina Crantz. (Brassicaceae) and insights on the origin of gold-of-pleasure (Camelina sativa). Molecular Phylogenetics and Evolution.
Hovsepyan R., Willcox G. 2008. The earliest finds of cultivated plants in Armenia: evidence from charred remains and crop processing residues in pisé from the Neolithic settlements of Aratashen and Aknashen. Vegetation History and Archaeobotany, v.17, s.1, pp. 63-71.