Petuniaflowers solve the defence/apparency dilemma of pollinator attraction by deploying complex floral blends

Abstract

Flowers recruit floral visitors for pollination services by emitting fragrances. These scent signals can be intercepted by antagonists such as florivores to locate host plants. Hence, as a consequence of interactions with both mutualists and antagonists, floral bouquets likely consist of both attractive and defensive components. While the attractive functions of floral bouquets have been studied, their defensive function has not, and field-based evidence for the deterrence of floral-scent constituents is lacking. In field and glasshouse experiments with five lines of transgenic Petunia x hybrida plants specifically silenced in their ability to release particular components of their floral volatile bouquet, we demonstrate that the emission of single floral-scent compounds can dramatically decrease damage from generalist florivores. While some compounds are used in host location, others prevent florivory. We conclude that the complex blends that comprise floral scents are likely sculpted by the selective pressures of both pollinators and herbivores.

Floral Scent Contributes to Interaction Specificity in Coevolving Plants and Their Insect Pollinators

“…Under this hypothesis, volatile compounds with emission rates most strongly tailored towards the daytime may be especially important for interaction with Greya moths. Recent studies highlight the repellent functions of some floral volatiles (Junker and Blüthgen 2013;Kessler et al 2013), suggesting that volatiles with more constant emission rates across days and nights might have functions other than pollinator attraction. Hence, it is possible that the variation in scent composition and species-specific day vs. night emission patterns in the three Lithophragma species studied here could reflect selective forces other than the specialist Greya moths and the sometimes significant impact of generalist pollinators (see Thompson and Cunningham 2002).…”

The raison d'être of chemical ecology

“…Selective knockdown of floral nicotine modified pollinator behavior, as predicted from bioassays with artificial flowers, but also increased nectar-robbing behavior by carpenter bees and florivory by noctuid moth larvae ). These and similar experiments (Kessler et al 2012b), made possible through increased understanding of complex biosynthetic pathways, reveal the hand of chemistry in shaping both the presence and absence of links in complex ecological networks.…”

“…However, more generalized plant-pollinator interactions tend to be mediated by generic volatiles that are innately attractive to diverse groups of pollinators, or are easily learned by them in association with nectar-or pollen-based floral resources (Raguso 2008). Furthermore, the diversity of visitors to generalized flowers appears to select for multifunctional compounds (volatile or not) that simultaneously repel enemies and attract pollinators or adaptively modify their behavior (Galen et al 2011, Kessler et al 2012b. Multifunctionality is emerging as one of the most important and common attributes of natural products, which is surprising in the light of their great structural diversification.…”

Volatile terpenoids: multiple functions, biosynthesis, modulation and manipulation by genetic engineering

“…The transformation of petunia with the (S)-limonene synthase gene from C. breweri results in linalool production that repels aphids (Lücker et al 2001). The repellent/attraction properties of various terpenoid volatiles in petunia flower were observed via silencing the biosynthetic genes individually responsible for the production of scent compounds (Kessler et al 2013). Another example of floral scent engineering is the introduction of a maize sesquiterpene synthase gene (TPS10) into Arabidopsis, leading to the production of a significant amount of various sesquiterpenes that are exploited by the female parasitoid wasp C. marginiventris to navigate to their potential lepidopteran host (Schnee et al 2006;Delory et al 2016).…”