Botanists discover not all clones are the same, it depends on how you make them

Seeds can travel great distances, and a lucky plant can make a successful life in a new location. But this doesn’t make much difference if it cannot pass its luck on to the next generation. Verena Reutemann and colleagues in Argentina and Germany examined what advantages there were when a plant could produce offspring with just one parent. Their results, published in the Botanical Journal of the Linnean Society, show that producing clones is an advantage, but not all clones are the same.

Paspalum is a genus of grasses from South America that come in diploid forms, with just two copies of their genome in their cells, or polyploid forms, with three or more copies. The polyploidy suggests they have a relaxed attitude to the results of sex, but they also have a relaxed attitude to the process. They can reproduce sexually, but also by self-fertilisation if they cannot find a partner. They can also reproduce by apomixis, where the seeds aren’t fertilised at all. This variety of approaches in similar species makes them suitable for studying how sexual strategy affects a plant’s range, say Reutemann and colleagues. “Only a few plant systems enable the study of the effects of uniparental reproduction in nature. Paspalum L. is among the richest genera of Poaceae with c. 350 species showing contrasting genetic systems, allowing the analysis of the consequences of uniparentality and its role in shaping plant distributions.”

The study of Paspalum showed that the range of a species varied depending on its sex life. Plants that could use uni-parental strategies, such as self-fertility or apomixis, where seeds do not need to be fertilised, allow these plants to cover a wider geographic range than plants using sexual reproduction. Reutemann and colleagues found that for some multiploid plants there was competition between varieties, or cytotypes, that used self-fertility and those that used apomixis. The team found that the contest for territory allowed both forms to coexist in a region. Reuteman and colleagues say that this ability to have just one parent can have advantages when it comes to expanding a plant’s range.

“Unlike self-fertile (uniparental) species, self-sterile ones (biparental) cannot produce a new generation without a reproductive partner, and this is expected to impose disadvantages for colonization of new areas. The independence from foreign pollen sources makes selfers more successful in new habitat colonization and increases chances of establishing a new population relative to self-sterile or dioecious species… Also, selfing plays a major role in the newly colonized area, where the lack of pollinators or compatible reproductive partners produces a pollen limitation affecting seed production…”

The researchers add that the reproduction method has implications for the ploidy of the plants. Plants that can reproduce through self-fertilisation can gain the benefits of uniparentality without having to give up diploidy and the possibility of outcrossing genes with other sexual partners. Apomixis, in contrast, favours polyploids. Once plants have differing ploidy levels, reproductive barriers can isolate the cytotypes from each other.

The results show that while plants can copy themselves by producing clones, the way they do it means not all clones are the same. Their study sheds new light on how sexual strategy can influence the distribution of genotypes.

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Reutemann, A.V., Martínez, E.J., Schedler, M., Daviña, J.R., Hojsgaard, D.H. and Honfi, A.I. (2022) “Uniparentality: advantages for range expansion in diploid and diploid-autopolyploid species,” Botanical Journal of the Linnean Society. https://doi.org/10.1093/botlinnean/boac036