Does Increasing Chromosome Sets Change Floral Scent?

Plants sometimes undergo polyploidization, an increase in the number of chromosome sets. Flower size and other traits can change, but does the scent attracting insects change too? A further question is whether changes occur immediately after the increase or develop over a long period of subsequent evolution.

In 2025, Elisabeth Schlager and colleagues investigated this question in Lithophragma bolanderi, a plant in the saxifrage family. They compared naturally occurring diploids and tetraploids with newly created experimental polyploids, analyzing scent emission, compound richness, and blend proportions.

What distinguishes diploids and tetraploids?

Chromosomes carry genetic information. Diploids have two basic chromosome sets; tetraploids have four. The change here concerns the number of complete sets, not the addition of a single chromosome.

The study species is a perennial native to California, USA. Earlier research showed that small Greya moths pollinate its flowers and that scent is an important attraction cue. The researchers used plants originating from one population in which diploids and tetraploids coexist.

Even if established natural diploids and tetraploids differ in scent, that alone does not identify polyploidization as the direct cause. Selection over time or the chance accumulation of genetic differences could also contribute. Examining newly formed polyploids helps separate these possibilities.

Treating parents and examining 84 plants in the next generation

The researchers treated diploid seedlings with colchicine to induce polyploidization. They crossed these plants and examined floral scent in the next generation, the F1, to reduce treatment side effects. Parental seedlings of control diploids and tetraploids received water instead of the chemical.

The analysis included 84 plants: 22 diploids and 22 tetraploids from natural lineages, plus descendants of treated parents comprising 17 plants that remained diploid, 16 new triploids, and seven new tetraploids.

Triploids also arose, possibly because some parents contained a mixture of cells of different ploidy. Chemical treatment does not turn every plant neatly into a tetraploid.

Open flowers were enclosed in bags and scent compounds collected from the air for 15 minutes at room temperature. An average of about ten flowers per plant was sampled together, and emission was calculated relative to flower number and time. Gas chromatography–mass spectrometry separated and analyzed compounds, with empty bags, leaves, and other controls also sampled.

Naturally derived tetraploids emitted more and contained more compounds

Across all 84 samples, 42 floral scent compounds were detected. Five, including linalool, methyl benzoate, and methyl salicylate, occurred in every sample. Other compounds were detected only in particular groups.

Comparing diploids and tetraploids from natural lineages, tetraploids emitted a larger amount of scent per flower and contained a greater number of detected compounds. Relative proportions, meaning each compound’s share of the total blend, also differed.

Three distinct properties are being considered: greater emission, more kinds of compounds, and different mixing proportions. They are not direct measures of perceived intensity for humans or attractiveness to moths.

Changes were also evident in new tetraploids

Compared with diploids from natural lineages, newly formed tetraploids had greater compound richness and different blend proportions. The difference in emission rate, however, was not significant.

Blend proportions also differed between new tetraploids and tetraploids from natural lineages. Acquiring four chromosome sets therefore does not immediately produce the same scent blend as established natural tetraploids.

The authors highlight that changes in new tetraploids were generally in the same direction as the differences between natural diploids and tetraploids, but smaller. They interpret this as suggesting that later evolutionary changes may build on changes arising immediately after polyploidization.

The difficulty of separating treatment effects from polyploidization

An important comparison is the group descended from chemically treated parents that nevertheless remained diploid. This group also differed from naturally derived diploids, having fewer detected compounds. Even using the next generation may not completely eliminate treatment effects or differences among treatment-derived lineages.

Compared with this treatment-derived diploid group, new tetraploids tended to emit more scent, with a significant difference before adjustment. However, after statistical correction for multiple comparisons, the difference was no longer significant. Neither compound richness nor blend proportions differed significantly between these two groups.

Thus, although new tetraploids showed changes, caution is still needed before asserting that increasing chromosome sets alone immediately increases emission. The symbols indicating differences in the paper’s figure also reflect unadjusted tests, making it important to distinguish the comparison group and the corrected results.

There were only seven new tetraploids. The study also conducted analyses accounting for parental seed-family differences, but restricting comparisons to the same crossing lineage further reduced sample sizes, and many differences were not significant. The authors call for larger samples and work that better separates chemical-treatment effects from polyploidization effects.

What if moths choose between the different scents?

The study also concerns how scent changes could affect plant evolution. If moths distinguish diploid and tetraploid scents and repeatedly visit similarly scented flowers, pollen might be transferred more often between plants of the same ploidy.

Such biased visitation could help newly formed polyploids establish in a population and diverge further from the original diploids. The authors propose a pathway in which polyploidization produces initial scent differences, which pollinator-mediated selection subsequently strengthens.

However, the study did not test moth flower choices or measure polyploid reproductive success. Earlier studies showed antennal responses to relevant scent compounds and moth discrimination among floral scents from different regions, but whether moths use these particular ploidy-related differences needs separate testing.

The research received support from organizations including the Swiss National Science Foundation, the Swedish Research Council, and the Wenner-Gren Foundations. The authors declared no competing interests.

Summary

In Lithophragma bolanderi, diploids and tetraploids from natural lineages differed in scent emission, compound richness, and blend proportions. New tetraploids also differed from naturally derived diploids in richness and proportions, but assessing direct effects separately from chemical-treatment effects remains challenging.

The authors suggest that increasing chromosome sets can be considered a starting point for scent diversification, not only changes in flower shape. How do insects perceive the small differences that arise, and how does this affect subsequent pollen transfer? Connecting those steps could illuminate how plants and pollinators diversify through their interactions.

References

Schlager, E., Dötterl, S., Thompson, J. N., Friberg, M., & Gross, K. (2025). Direct Effects of Polyploidization on Floral Scent. Journal of Chemical Ecology, 51, 89. DOI: 10.1007/s10886-025-01641-y. Full text. © The Author(s) 2025. The original article is published under CC BY 4.0.