Flower Production, Headspace Volatiles, Pollen Nutrients, and Florivory in Tanacetum vulgare Chemotypes

Abstract

Floral volatiles and reward traits are major drivers for the behavior of mutualistic as well as antagonistic flower visitors, i.e., pollinators and florivores. These floral traits differ tremendously between species, but intraspecific differences and their consequences on organism interactions remain largely unknown. Floral volatile compounds, such as terpenoids, function as cues to advertise rewards to pollinators, but should at the same time also repel florivores. The reward composition, e.g., protein and lipid contents in pollen, differs between individuals of distinct plant families. Whether the nutritional value of rewards within the same plant species is linked to their chemotypes, which differ in their pattern of specialized metabolites, has yet not been investigated. In the present study, we compared Tanacetum vulgare plants of five terpenoid chemotypes with regard to flower production, floral headspace volatiles, pollen macronutrient and terpenoid content, and floral attractiveness to florivorous beetles. Our analyses revealed remarkable differences between the chemotypes in the amount and diameter of flower heads, duration of bloom period, and pollen nutritional quality. The floral headspace composition of pollen-producing mature flowers, but not of premature flowers, was correlated to that of pollen and leaves in the same plant individual. For two chemotypes, florivorous beetles discriminated between the scent of mature and premature flower heads and preferred the latter. In semi-field experiments, the abundance of florivorous beetles and flower tissue miners differed between T. vulgare chemotypes. Moreover, the scent environment affected the choice and beetles were more abundant in homogenous plots composed of one single chemotype than in plots with different neighboring chemotypes. In conclusion, flower production, floral metabolic composition and pollen quality varied to a remarkable extend within the species T. vulgare, and the attractiveness of floral scent differed also intra-individually with floral ontogeny. We found evidence for a trade-off between pollen lipid content and pollen amount on a per-plant-level. Our study highlights that chemotypes which are more susceptible to florivory are less attacked when they grow in the neighborhood of other chemotypes and thus gain a benefit from high overall chemodiversity.

Floral Scents and Fruit Aromas: Functions, Compositions, Biosynthesis, and Regulation

“…Their selection behavior depends on differences in composition, amount, and emission of floral volatile compounds ( Muhlemann et al, 2014 ). For instance, emitted terpenoids and benzenoids can attract pollinators and repel elective visitors ( Farré-Armengol et al, 2013 ), while the same terpenoid compound may attract one animal but repel another ( Eilers et al, 2021 ). Many flowers offer floral rewards as nectar, pollen or oil products, on which visitors depend ( Steiner et al, 2011 ) but some plants attract pollinators without offering nectar by mimicking the scents and colors of neighboring plants ( Kunze, 2001 ; Schiestl, 2005 ).…”

Chemical phenotype as important and dynamic niche dimension of plants

“…Just as the niche, chemodiversity does hugely vary across species (Schweiger et al ., 2021) and populations (Li et al ., 2015; Ginigini et al ., 2019), but also among individuals within species (e.g. Bustos‐Segura et al ., 2017; Glassmire et al ., 2019; Eilers et al ., 2021; reviewed in Kessler & Kalske, 2018; Wetzel & Whitehead, 2020). Niche theory provides the required mechanistic framework to understand and explain the observed dynamic diversity in metabotypes.…”

Intra-Individual and Intraspecific Terpenoid Diversity in Erodium cicutarium

“…Therefore, E. cicutarium is a very interesting species to study the role of pollinator-independent floral volatiles. In comparison, the constitutive foliar and floral terpenoid compositions of a highly pollinator-dependent plant with immense terpenoid diversity in plant tissues, Tanacetum vulgare (Asteraceae), are similar, leading to comparable chemotypes in flowers and leaves [33,34]. Because the attraction of beneficial organisms may not play a major role for the chemical composition of E. cicutarium plant parts, the detected compounds (mostly terpenoids) potentially function as herbivore repellent or act against competing plants.…”

“…Secondly, it was expected that the chemotypes of leaves, blossoms and fruits within plant individuals would be correlated because terpenoids of particularly high abundance in leaves would also be present in flowers and fruits of the same plants. In other plants such as Tanacetum vulgare, the terpenoids with the highest compound abundance, which shape the terpenoid chemotypes in leaves, are also found in high abundance in inflorescences [33,34]. Thirdly, it was hypothesized that the diversity of contained terpenoids would be high in plants from both, the native and the invaded range.…”