A reassessment of the genome size – invasiveness relationship in reed canary grass

The smaller a plant's genome, the more likely it is to be invasive? Or so it was thought but newer techniques are casting some doubt on the idea.

What is it that can make a plant invasive? There’s no clear answer because a combination of factors can help. Also, different traits may play a role at different stages of an invasion. Pulling apart the ingredients of a successful invader is means accounting for many traits at the same time.

Reed canary grass, Phalaris arundinacea

The feature Martinez and colleagues look at in their article is the relationship between genome size and invasiveness. They look back to an earlier key study by Lavergne et al. on Phalaris arundinacea. Lavergne’s paper concluded: “This study provides preliminary evidence that a sudden reduction in genome size, probably occurring over very few generations, may result in rapid phenotypic evolution.” meaning a plant that reduced its genome size could become a lot more flexible in how it adapted to a change in environment.

However, since 2010 Lavergne et al.’s results have started looking more unusual. Since the study, more accurate tools have become more widely available for examining genome size. Martinez and colleagues thought to reexamine P. arundinacea with newer methods and older methods to see if Lavergne’s results still hold up.

What they found was there was no significant difference in genome size between native and invasive range P. arundinacea. They also found no relationship between genome size and growth rates in their North American samples.

Martinez et al. say: “We suspect that the differences between our findings and those of previous studies may be traced to our use of the best-practice flow cytometric protocol for genome size estimation in plants, rather than to differences in population sampling: we were able to replicate previous patterns by using the older pseudo-internal protocol.” That extra work means Martinez and colleagues aren’t asking you simply to choose which result you prefer, but giving a reason why their new results are still consistent with Lavergne et al.’s old results – despite contradicting them.

Martinez’s paper concludes by noting their own results pose a bit of a problem: “How do we reconcile our findings of no genome size–invasiveness relationship within P. arundinacea with cross-species results indicating a general association between small genome size and invasive behaviour in plants?” They answer by outlining three ways research into genome size and invasiveness can move forward, using newer techniques.

Further reading

Martinez, M. A., Baack, E. J., Hovick, S. M., & Whitney, K. D. (2018). A reassessment of the genome size–invasiveness relationship in reed canarygrass (Phalaris arundinacea). Annals of Botany, 121(7), 1309–1318. https://doi.org/10.1093/aob/mcy028

Lavergne, S., Muenke, N. J., & Molofsky, J. (2009). Genome size reduction can trigger rapid phenotypic evolution in invasive plants. Annals of Botany, 105(1), 109–116. https://doi.org/10.1093/aob/mcp271

Bock, D. G., Caseys, C., Cousens, R. D., Hahn, M. A., Heredia, S. M., Hübner, S., … Rieseberg, L. H. (2015). What we still don’t know about invasion genetics. Molecular Ecology, 24(9), 2277–2297. https://doi.org/10.1111/mec.13032