Plant Diversity – PPP2019

EDIT: This post was written at the symposium as it happened. It has now been edited to correct some errors made while working rapidly, fix links, and add tweets from other people at the symposium.

Simon Hiscock started with a reminder that we’ve only accepted plants have sex for about 300 years. Thomas Fairchild created a hybrid of a Carnation and Sweet William. Fairchild’s Mule was a sterile hybrid. The zoocentric idea of sex has set the idea of species. So while breeding is important to animals, plants hybridise, self-pollinate and undergo shifts to polyploidy. 25% of plant species and 10% animal species can hybridise with other species.

Hiscock ran through various forms of hybrid speciation, Homoploidy, where the hybrid has the same number of chromosomes as the parents, and allopolyploidy where the chromosomes are doubled.

Hiscock started looking at Sorbus Whitebeam. Whitebeam is a tree that seems to create also sorts of new species and hybrids. Clifton gorge is a hotspot if you want to see a plant that is staggeringly rare, but the dynamic process of evolution is ongoing creating new forms. Hiscock suggested making all Sorbus protected, not just the rare forms, as the value here is in the generative process that creates all these new forms.

Senecio, Oxford ragwort, came to Oxford from Etna. It arrived in 1700. Since the 1800s the railways have helped it spread across the UK. It’s also started hybridised with native Senecio. Oxford ragwort is itself a hybrid of two plants from Mount Etna.

The hybrid zone between Senecio aethnensis and S. chrysanthemifolius on Mount Etna, Sicily, provides a well-studied example of species divergence in response to conditions at different elevations, despite hybridization and gene flow. These results show that the two Senecio species, while subject to gene flow, maintain divergent genomic regions consistent with local selection within species and selection against hybrids between species which, in turn, contribute to the maintenance of their distinct phenotypic differences.

The homoploid hybrid ragwort species, Senecio squalidus (Oxford ragwort), originated following the introduction of hybrid plants to the UK approximately 320 years ago. The source of the hybrid plants was from a naturally occurring hybrid zone between S. aethnensis and S. chrysanthemifolius on Mount Etna, Sicily.

These findings suggest that this young homoploid hybrid species has inherited a unique combination of genomic rearrangements and incompatibilities from its parents that contribute to its reproductive isolation.

While polyploidy is a headache, it’s only going to become more The future of plant evolution will be of an influence in evolution, according to Donald Levin.

Talk by Susanne Renner

Susanne Renner said that watermelon is a small genus. So why don’t we know when it was domesticated? The origin of watermelon is confusing. The original Citrullus lanatus type specimen wasn’t actually a part of what is now recognised as that species. It’s Citrullus amarus.

Other species are grown for their seeds. Another as a diuretic and maybe to induce abortions. Renner also showed a spiky watermelon. They’re all bitter, apart from Citrullus lanatus.

Archaeological evidence shows watermelon was cultivated 3500 years ago. Or so I thought. Renner showed Citrullus seeds from 5000BP from Uan Muhuggiag in Libya. Harry Paris has also concluded a north-east Africa origin for watermelon.

DNA analysis of melon from Egypt shows the plants they had were sweet and had red pulp. Renner points out that people learn from each other. Knowledge isn’t bound to inheritance. “We don’t need to have sex to have the same iPhone.”

So, it looks like there could be a NE Africa origin for watermelon, but still too early to say who or where exactly it originated. Renner also pointed out that vegetation ranges have changed massively in the Sahara region over thousands of years. The closest relative today is found in Darfur, but what was the vegetation like six or eight thousand years ago?

Talk by Eric von Wettberg

Eric von Wettberg kept us in Africa with the Queen of Sheba’s chickpeas. He’s recently published work on genetic diversity showing the path of chickpea domestication.

His talk started with a nod to Vavilov. The Vavilov Genebank has stores of pre-Green Revolution chickpea, which can give information on domestication origins. Domestication is a puzzle as chickpea disappears for 2000 years from the archaeological record. Von Wettberg has records of where Vavilov collected chickpea samples. Road distance rather than geographic distance correlated better with the dispersal of chickpeas, which suggests people were exchanging seeds along established trade routes. Despite this 2000 year disappearance, it doesn’t seem that chickpeas were re-imported from South Asia, so where did they go?

And what about the Queen of Sheba’s chickpeas? Studies of Ethiopian chickpeas seem to be a mix of Turkish and Central Asian sources. In Ethiopia it dates to about 3500 years ago.

Talk by Oscar Alejandro Pérez-Escobar

I had nothing on Oscar Alejandro Pérez-Escobar, tracing the domestication of the date palm. That’s because it’s a paper in progress, and that’s why I’m wary of blogging too much, as I don’t want to interfere with publication process.

I didn’t know date palm was one of the earliest domesticated tree crops. Zehdi-Azouzi and colleagues have argued for at least two origins.

Pérez-Escobar will have interesting results when you can read them. He’s been studying 3500 year old material from Kew’s archaeobotanical collection. It’s difficult. Of 4000 million reads of the DNA just 0.008% were palm aDNA.

Talk by Adriane Tobias

I don’t have anything on Adriane Tobias on Rafflesia banoana either. This is a talk from Tobias’s PhD thesis, so that’s part of the reason. The other is Rafflesia banaoana was described in 2010.

While you can find Rafflesia elsewhere in south east Asia, there are 14 species of Rafflesia, for now, endemic to the Philippines. Loss of forest is removing habitat for Rafflesia, and many of the species are found in just one location. Rafflesia leonardi has found in one location of Luzon island. The last expedition to see it didn’t find it, due to a typhoon in 2018.

Or has it disappeared? Some people have argued that Rafflesia banoana is the same species as Rafflesia leonardi, just a different size. Tobias has fairly strongly demonstrated they’re not. While size can be variable, there are strong morphological differences. I’ll have to look out for publication from that thesis.

For a session on diversity, it’s no surprise that the papers were diverse. I think a common feature is the importance of taxonomy. Without reliable taxonomy you can’t have common ground for discussing diversity. Tobias concluded linking taxonomy and conservation. It’s a chilling thought that some species will only be preserved in the scientific record. Records can be powerful. The work of Renner, von Wettberg and Perez-Escobar shows this. But records are still not a replacement for the plant material as Hiscock showed. Diversity of plants is good, but we also need diversity of scientific sources.

Further reading

Brennan, A. C., Harris, S. A., & Hiscock, S. J. (2013). The Population Genetics of Sporophytic Self-incompatibility in Three Hybridizingsenecio(Asteraceae) Species with Contrasting Population Histories. Evolution, no–no. https://doi.org/10.1111/evo.12033

Brennan, A. C., Hiscock, S. J., & Abbott, R. J. (2014). Interspecific crossing and genetic mapping reveal intrinsic genomic incompatibility between two Senecio species that form a hybrid zone on Mount Etna, Sicily. Heredity, 113(3), 195–204. https://doi.org/10.1038/hdy.2014.14

Brennan, A. C., Hiscock, S. J., & Abbott, R. J. (2016). Genomic architecture of phenotypic divergence between two hybridizing plant species along an elevational gradient. AoB Plants, 8, plw022. https://doi.org/10.1093/aobpla/plw022

Brennan, A. C., Hiscock, S. J., & Abbott, R. J. (2019). Completing the hybridization triangle: the inheritance of genetic incompatibilities during homoploid hybrid speciation in ragworts (Senecio). AoB PLANTS, 11(1). https://doi.org/10.1093/aobpla/ply078

Chapman, M. A., Hiscock, S. J., & Filatov, D. A. (2015). The genomic bases of morphological divergence and reproductive isolation driven by ecological speciation inSenecio(Asteraceae). Journal of Evolutionary Biology, 29(1), 98–113. https://doi.org/10.1111/jeb.12765

Chomicki, G., & Renner, S. S. (2014). Watermelon origin solved with molecular phylogenetics including Linnaean material: another example of museomics. New Phytologist, 205(2), 526–532. https://doi.org/10.1111/nph.13163

Chomicki, G., Schaefer, H., & Renner, S. S. (2019). Origin and domestication of Cucurbitaceae crops: insights from phylogenies, genomics and archaeology. New Phytologist. https://doi.org/10.1111/nph.16015

Levin, D. A. (2019). Plant speciation in the age of climate change. Annals of Botany. https://doi.org/10.1093/aob/mcz108

Paris, H. S. (2015). Origin and emergence of the sweet dessert watermelon,Citrullus lanatus. Annals of Botany, 116(2), 133–148. https://doi.org/10.1093/aob/mcv077

Plekhanova, E., Vishnyakova, M. A., Bulyntsev, S., Chang, P. L., Carrasquilla-Garcia, N., Negash, K., … Nuzhdin, S. V. (2017). Genomic and phenotypic analysis of Vavilov’s historic landraces reveals the impact of environment and genomic islands of agronomic traits. Scientific Reports, 7(1). https://doi.org/10.1038/s41598-017-05087-5

Renner, S. S., Pérez-Escobar, O. A., Silber, M. V., Nesbitt, M., Preick, M., Hofreiter, M., & Chomicki, G. (2019). A 3500-year-old leaf from a Pharaonic tomb reveals that New Kingdom Egyptians were cultivating domesticated watermelon. https://doi.org/10.1101/642785

Vallejo‐Marín, M., & Hiscock, S. J. (2016). Hybridization and hybrid speciation under global change. New Phytologist, 211(4), 1170–1187. https://doi.org/10.1111/nph.14004

Varma Penmetsa, R., Carrasquilla‐Garcia, N., Bergmann, E. M., Vance, L., Castro, B., Kassa, M. T., … Cook, D. R. (2016). Multiple post‐domestication origins of kabuli chickpea through allelic variation in a diversification‐associated transcription factor. New Phytologist, 211(4), 1440–1451. https://doi.org/10.1111/nph.14010

Von Wettberg, E. J. B., Chang, P. L., Başdemir, F., Carrasquila-Garcia, N., Korbu, L. B., Moenga, S. M., … Cook, D. R. (2018). Ecology and genomics of an important crop wild relative as a prelude to agricultural innovation. Nature Communications, 9(1). https://doi.org/10.1038/s41467-018-02867-z

Varshney, R. K., Thudi, M., Roorkiwal, M., He, W., Upadhyaya, H. D., Yang, W., … Liu, X. (2019). Resequencing of 429 chickpea accessions from 45 countries provides insights into genome diversity, domestication and agronomic traits. Nature Genetics, 51(5), 857–864. https://doi.org/10.1038/s41588-019-0401-3

Weeden, N. F. (2007). Genetic Changes Accompanying the Domestication of Pisum sativum: Is there a Common Genetic Basis to the “Domestication Syndrome” for Legumes? Annals of Botany, 100(5), 1017–1025. https://doi.org/10.1093/aob/mcm122

Zehdi-Azouzi, S., Cherif, E., Moussouni, S., Gros-Balthazard, M., Abbas Naqvi, S., Ludeña, B., … Aberlenc-Bertossi, F. (2015). Genetic structure of the date palm (Phoenix dactylifera) in the Old World reveals a strong differentiation between eastern and western populations. Annals of Botany, 116(1), 101–112. https://doi.org/10.1093/aob/mcv068