The Secret Genetic Code of Invasive Plants

Petr Pyšek and a team of researchers from institutions across Europe, China and the USA wanted to understand why some plant species become invasive when introduced outside their native range. This question is important because invasive species can cause severe damage to ecosystems and cost billions to control.

The researchers analysed data on over 11,000 plant species from around the world to explore how two key genetic factors – genome size and ploidy – affect the different stages of invasion. Genome size refers to the total amount of DNA contained in the cells of an organism. Ploidy is the number of sets of chromosomes; for example, diploid plants have two sets, while tetraploids have four.

By compiling massive global datasets, the team could robustly test the links between these genetic traits and invasion success. They aimed to shed light on why certain plants become problematic invaders in new regions. The findings, published in New Phytologist, have important implications for predicting and managing biological invasions.

Gathering the Evidence

The researchers gathered an enormous data set drawn from plant species from all over the planet. This included 10,400 flowering plant (angiosperm) species, 379 gymnosperms (like conifers), 218 ferns and 52 clubmosses.

The data on genome sizes and chromosome numbers came from the Royal Botanic Gardens Kew’s Plant DNA C-values Database. This represents the most comprehensive compilation of plant genome size measurements globally. The researchers also searched the scientific literature to add genome size data for a further 40 species not yet in the database.

Information on which plant species have become naturalised or invasive when introduced outside their native regions came from the Global Naturalised Alien Flora (GloNAF) database. This data covers 13,939 naturalised alien plant species across over 1,000 regions worldwide. For a subset of 349 regions, there were also data available on which naturalised species have become invasive.

Compiling such a massive data set for so many plant species allowed the researchers to analyse the links between genome size, chromosome number and invasion success. One limitation was that chromosome counts were not available for all species, making it impossible to determine accurate ploidy levels in some cases. Despite this, the scale of the data set gave immense power to detect general trends.

Contrasting Effects at Different Invasion Stages

The analysis revealed that plant species with small genomes were more likely to become naturalised outside their native range. Naturalised species can form self-sustaining populations in the new region without human intervention.

However, the story was different when looking at invasive spread and ecological impacts. Large genome sizes and higher ploidy levels provided an advantage for a naturalised species to progress to become a problematic invader that spreads rapidly and causes environmental damage.

The researchers quantified naturalisation success in two ways – whether a species was naturalised anywhere in the world and the number of regions it had naturalised in. They also looked at the number of regions where a species had become invasive.

Species with intermediate-sized genomes were naturalised or invasive in the most regions globally. However, large genomes supercharged the ability of an alien species to spread invasively and negatively impact native biodiversity and ecosystems.

The contrasting effects at the naturalisation versus invasion stages show that genome size and ploidy level play different roles in the progression from introduced species to problematic invaders.

Why Do Genome Size and Ploidy Have Contrasting Effects?

The findings suggest some explanations why small genomes promote naturalisation while large genomes and high ploidy assist invasive spread.

• Small genomes allow introduced plants to adapt quickly to new environmental conditions in the regions they are introduced to. This rapid evolution enhances their ability to establish sustainable populations.
• In contrast, large genomes and extra sets of chromosomes provide traits that favour invasive spread, like vigorous growth, high reproductive output, and efficient dispersal of seeds or vegetative fragments.

The two factors interact – species with relatively small genomes combined with higher ploidy seem able to maximise the benefits for invasiveness. The small genomes aid adaptation. At the same time, extra chromosomes supercharge growth and reproduction. The researchers found that while polyploids alone were more likely to naturalise than diploids, the highest naturalisation success was for species reported to include both diploid and polyploid individuals. They suggest this diploid-polyploid combination maximises variability, providing greater genetic potential for adaptation to new environments.

The Key Role of Genetics in Plant Invasions

This research reveals that two fundamental genetic factors – genome size and ploidy – play vital but contrasting roles in enabling plants to become successful invaders. Their effects change depending on the invasion stage. Small genomes assist naturalisation by allowing rapid adaptation to new environments. However, large genomes and high ploidy boost invasive spread by providing traits like vigorous growth and reproduction. These new insights help explain why some plant species become problematic invaders in regions outside their native ranges. The findings also showcase the context-dependent nature of biological invasions, with the influence of species traits and genetics shifting between invasion phases. 

The study powerfully demonstrates the value of amassing massive global data sets to identify general trends. Compiling data on over 11,000 plant species was crucial for unravelling the nuanced relationships between genome size, ploidy and invasive success. This big data approach points the way for better understanding and predicting invasion biology.

READ THE ARTICLE
Pyšek, P., Lučanová, M., Dawson, W., Essl, F., Kreft, H., Leitch, I.J., Lenzner, B., Meyerson, L.A., Pergl, J., van Kleunen, M., Weigelt, P., Winter, M. and Guo, W.-Y. (2023) “Small genome size and variation in ploidy levels support the naturalization of vascular plants but constrain their invasive spread,” New Phytologist, 239(6), pp. 2389–2403. Available at: https://doi.org/10.1111/nph.19135.