Differences in Floral Scent and Petal Reflectance Between Diploid and Tetraploid Chamerion angustifolium

Abstract

Genome duplication in plants is thought to be a route to speciation due to cytotype incompatibility. However, to reduce cross-pollination between cytotypes in animal-pollinated species, distinctive floral phenotypes, which would allow pollinator-mediated assortative mating between flowers, are also expected. Chamerion angustifolium is a Holarctic species that forms a hybrid zone between diploid and tetraploid populations in the North American Rocky Mountains. Extensive research has shown that these cytotypes differ in many ways, including some floral traits, and that pollinators can discriminate between cytotypes, leading to assortative mating. However, two signals commonly used by insect pollinators have not been measured for this species, namely petal colour and floral scent. Using greenhouse-grown diploids and tetraploids of C. angustifolium from the ploidy hybrid-zone in the North American Rocky Mountains, we show that both floral scent signals and petal reflectance differ between cytotypes. These differences, along with differences in flower size shown previously, could help explain pollinator-mediated assortative mating observed in previous studies. However, these differences in floral phenotypes may vary in importance to pollinators. While the differences in scent included common floral volatiles readily detected by bumblebees, the differences in petal reflectance may not be perceived by bees based on their visual sensitivity across the spectra. Thus, our results suggest that differences in floral volatile emissions are more likely to contribute to pollinator discrimination between cytotypes and highlight the importance of understanding the sensory systems of pollinators when examining floral signals.

Induced polyploidy deeply influences reproductive life cycles, related phytochemical features, and phytohormonal activities in blackberry species

“…The features of the reproductive organs, including inflorescence size, floral display, color, scent chemistry, and nectar quantity, can affect pollinator behavior and pollination efficiency (Husband and Schemske, 2000;Anssour et al, 2009;Balao et al, 2011). In line with the current results, both floral fragrance cues and petal reflectance changed across cytotypes of diploid and tetraploid flowers in Chamerion angustifolium (Palmqvist et al, 2021). Also, Davis et al (1994) reported that haploids of Brassica rapa yielded nectar carbohydrates three times less than those of its 2n and 4n lines, which is in general agreement with the findings of the current study.…”

Tropospheric Ozone Alters the Chemical Signal Emitted by an Emblematic Plant of the Mediterranean Region: The True Lavender (Lavandula angustifolia Mill.)

“…In addition, before introducing the plant into the chambers, to assess background scent level in the chambers, we collected, using the same method, blank samples, i.e., samples of air within empty chambers. Indeed, in semi-controlled experiments with whole plants, despite the fact that the air injected into the sampling chambers is purified with activated charcoal, exogenous compounds, which are considered as contaminants, are always present in the samples, and therefore must be removed from the plant samples (see methods in Palmqvist et al, 2021;Rupp et al, 2021). At the end of each O 3 exposure in the first experiment, inflorescences and leaves were cut from the plant and placed for 4 days at 40 • C in an oven to measure the dry biomass.…”

Polyploidy‐induced floral changes lead to unexpected pollinator behavior in Arabidopsis arenosa

“…Experimental work has shown different floral morphology and pollinator behaviors between natural polyploids (i.e. polyploids established in populations in the wild) and their presumed diploid progenitors, but not necessarily increased visitation of polyploids by pollinators (Segraves and Thompson 1999, Palmqvist et al 2021). However, such polyploids have undergone natural selection, and the direct effect of whole genome duplication cannot be derived from such experiments.…”

“…Thus, other mechanisms are likely to contribute to reproductive isolation between diploids and newly formed polyploids in early stages, such as assortative mating driven by pollinator shift. Differences in floral morphology and pollinator preference between diploids and established polyploids have been shown, leading to assortative mating (Segraves and Thompson 1999, Palmqvist et al 2021). Again, these may be explained by late‐acting selective processes rather than polyploidy itself.…”