Ashley Goland ’23
One enticing topic of research in the world of science is speciation, the process behind the formation of new and distinct species. Evening primroses (Onagraceae) are a family of flowers that model this procedure rather well. Now, there are numerous ways of defining a species, but when it comes to something like hybridization barriers, evening primroses exhibit multiple methods for researchers to learn from. Stony Brook assistant professor Jesse Hollister and three other researchers asked a few questions to this extent, and their answers yielded the first genome-wide scale evidence of how diversity and species origin are shaped by asexual reproduction and hybridization.
This research group amassed a sample representing thirteen species within the subsection Oenothera, consisting of twenty-five individual plants in total. The plants were placed in a growth chamber and cultivated for under sixteen hours of light at 25ºC and eight hours of dark at 20ºC. By graphically analyzing 60,518 sites of single nucleotide differences across these plants, the researchers discovered that heterozygosity varies between mating systems and genome complex combinations. Hybridization turned out to have major effects on genetic diversity patterns in permanent translocation heterozygotes. Also referred to as PTH species, these are organisms in which chromosomes have rearranged by exchanging segments between one another outside of their normal homologous pairs. Contrary to previous evidence, this study showed that most genetic diversity in PTH species comes from the hybridization of ancestral mutations that are then fixed as heterozygotes. Ultimately, the process described is what leads to new species. All of the results in this study point to hybridization between parents driving heterozygosity in PTH species.
The results of this study advance not only the knowledge base on evening primroses, but also reveal new insights toward the process of speciation as a whole. There is now evidence that a population’s rate of speciation can be accelerated by hybridization and asexual reproduction. Pursuing this thread further in upcoming years could unearth even more information on the inner workings of species divergence and deepen the world’s understanding of its asexual inhabitants.
 J. Hollister, et al., “Hybridization and a loss of sex shape genome‐wide diversity and the origin of species in the evening primroses (Oenothera, Onagraceae).” New Phytologist 224, 1372-1380 (2019). Doi: https://doi.org/10.1111/nph.16053
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